TCA peel

Trichloroacetic acid destroys tissue by protein denaturation. Depth is conventionally set by concentration, and the resulting white “frost” is coagulated protein — which is why TCA frost means something quite different from the crystallised acid you see after a salicylic peel.

It is used two ways: across a field, at 10–35%, as a superficial to medium-depth peel; and focally, at 65–100%, pressed into individual atrophic scars. Those are different procedures with different evidence, and this entry keeps them apart.

The most consequential section on this page, and the one least often taught.

The accepted pharmaceutical standard is weight-to-volume: grams of TCA made up to a final volume of 100 mL of solution.^{[1, 2]The accepted pharmaceutical standard for preparing TCA is weight-to-volume — grams of TCA made up to a final volume of 100 mL of solution.Directly tested by the source[1] Lee KC, Wambier CG, Soon SL, Sterling JB, Landau M, Rullan P, Brody HJ; International Peeling Society. Basic chemical peeling: superficial and medium-depth peels. Journal of the American Academy of Dermatology. 2019;81(2):313–324. doi:10.1016/j.jaad.2018.10.079Tier 4[2] Bridenstine JB, Dolezal JF. Standardizing chemical peel solution formulations to avoid mishaps. Great fluctuations in actual concentrations of trichloroacetic acid. J Dermatol Surg Oncol. 1994 Dec;20(12):813-816.Tier 3}

A laboratory comparison tested four preparation methods and found they produce concentrations that differ substantially from the label:

• Diluting a saturated solution labelled “100%” yielded the strongest actual concentration of the four tested — stronger than true weight-to-volume.^{[2, 1]Preparing TCA by weight-to-weight, by adding grams to 100 mL of water, or by diluting a saturated solution labelled '100%' produces concentrations that differ substantially from the label, and in the laboratory comparison the diluted-saturated-'100%' method yielded the strongest actual concentration of the four methods tested.Directly tested by the source[2] Bridenstine JB, Dolezal JF. Standardizing chemical peel solution formulations to avoid mishaps. Great fluctuations in actual concentrations of trichloroacetic acid. J Dermatol Surg Oncol. 1994 Dec;20(12):813-816.Tier 3[1] Lee KC, Wambier CG, Soon SL, Sterling JB, Landau M, Rullan P, Brody HJ; International Peeling Society. Basic chemical peeling: superficial and medium-depth peels. Journal of the American Academy of Dermatology. 2019;81(2):313–324. doi:10.1016/j.jaad.2018.10.079Tier 4}
• Adding grams of TCA to 100 mL of water is not weight-to-volume, and produced the weakest of the four.^{[2]Adding grams of TCA to 100 mL of water is not the same as weight-to-volume and produced the weakest of the four solutions tested, so the two phrasings are not interchangeable when ordering or labelling.Directly tested by the source[2] Bridenstine JB, Dolezal JF. Standardizing chemical peel solution formulations to avoid mishaps. Great fluctuations in actual concentrations of trichloroacetic acid. J Dermatol Surg Oncol. 1994 Dec;20(12):813-816.Tier 3}

So the two phrasings most people treat as synonyms sit at opposite ends of the range. If you dilute, order or label anything yourself, this is the difference between a superficial peel and a medium-depth one you did not consent the client for.

The practical position for most UK practitioners: buy pre-formulated solutions from a supplier who states the basis, and do not dilute a stock solution to reach a working strength.

Every course teaches the concentration-to-depth table. It is worth knowing what kind of knowledge it is.

It is expert and textbook material rather than measured histology.The review that carries it cites, as its authority, a book chapter written by two of the review’s own authors — and we located no primary study measuring TCA depth of injury against concentration in human skin.^{[1, 15]The depth-by-concentration table is expert/textbook material rather than measured histology: the JAAD review's stated authority for it is a Springer book chapter written by two of the review's own authors, Wambier and Brody.Directly tested by the source[1] Lee KC, Wambier CG, Soon SL, Sterling JB, Landau M, Rullan P, Brody HJ; International Peeling Society. Basic chemical peeling: superficial and medium-depth peels. Journal of the American Academy of Dermatology. 2019;81(2):313–324. doi:10.1016/j.jaad.2018.10.079Tier 4[15] Wambier CG, Brody HJ. Classification of chemical peels. In: da Costa A, ed. Minimally Invasive Aesthetic Procedures for Dermatologists and Plastic Surgeons. Springer Nature; 2019:1–12.Tier 4}

That does not make the convention wrong. Decades of practice sit behind it and it is the best framework available. It does mean the numbers are a professional consensus about where the boundaries fall, not readings off a measured curve — so treat them as a guide to selection and consent, not as a guarantee of what a given solution will do to a given face.

Frosting is graded in three levels, and with TCA it reflects epidermal and dermal protein denaturation. That much is well described.

What the review does notdo is map each level to a histological depth — and we searched and found no primary study validating any frost level against measured histology in the same skin.^{[no source found]The JAAD review defines three frost appearances clinically and says frosting reflects epidermal and dermal protein denaturation. It does NOT map each level to a histological depth. We searched and found no primary study validating any frost level against measured histology in the same skin.We looked and found no source either way} “Level III means you have reached the upper reticular dermis” is trained as fact and is not evidenced as one.

The depth-by-concentration table has the same shape of problem: the review’s stated authority for it is a Springer book chapter written by two of the review’s own authors.^{[1, 15]The depth-by-concentration table is expert/textbook material rather than measured histology: the JAAD review's stated authority for it is a Springer book chapter written by two of the review's own authors, Wambier and Brody.Directly tested by the source[1] Lee KC, Wambier CG, Soon SL, Sterling JB, Landau M, Rullan P, Brody HJ; International Peeling Society. Basic chemical peeling: superficial and medium-depth peels. Journal of the American Academy of Dermatology. 2019;81(2):313–324. doi:10.1016/j.jaad.2018.10.079Tier 4[15] Wambier CG, Brody HJ. Classification of chemical peels. In: da Costa A, ed. Minimally Invasive Aesthetic Procedures for Dermatologists and Plastic Surgeons. Springer Nature; 2019:1–12.Tier 4} And we found no primary human study measuring depth of injury against concentration either.^{[no source found]We searched on 2 August 2026 and found no primary human study measuring depth of injury against TCA concentration. That is our search result, not something the review establishes.We looked and found no source either way}

Use frost as it is actually described: a real-time signal of how vigorously the acid is working, telling you when to stop rather than precisely where you are.

Chemical Reconstruction Of Skin Scars — high-concentration TCA pressed hard into the depressed area of an individual atrophic scar, leaving the surrounding skin untouched. The best-evidenced TCA application.

The founding series covered 65 patients, all Fitzpatrick IV–V, with a good clinical response in 27 of 33 (82%) treated at 65% TCA and 30 of 32 (94%) treated at 100%, and no significant complications reported.^{[3]The CROSS technique — pressing high-concentration TCA hard into the whole depressed area of an atrophic scar — was described in 65 patients, all Fitzpatrick IV-V, with a good clinical response in 27 of 33 (82%) treated at 65% and 30 of 32 (94%) treated at 100%, and no significant complications reported.Directly tested by the source[3] Lee JB, Chung WG, Kwahck H, Lee KH. Focal treatment of acne scars with trichloroacetic acid: chemical reconstruction of skin scars method. Dermatol Surg. 2002 Nov;28(11):1017-1021.Tier 3}

Histology exists but is thin: serial focal 95% TCA over six treatments at six-week intervals produced, on paired biopsies at baseline and one year, decreased scar depth with increased collagen and fragmentation of elastic fibres — in three patients, uncontrolled.^{[4]Serial focal 95% TCA over six treatments at six-week intervals produced, on paired biopsies taken at baseline and one year, a decrease in scar depth with increased collagen fibres and fragmentation of elastic fibres — but in only three patients, uncontrolled.Directly tested by the source[4] Yug A, Lane JE, Howard MS, Kent DE. Histologic study of depressed acne scars treated with serial high-concentration (95%) trichloroacetic acid. Dermatol Surg. 2006 Aug;32(8):985-990.Tier 3}

Which scars, and at what strength

Against the alternatives — read this one carefully

Here the received wisdom needs splitting in two, because the caution and the technique it is usually applied to do not match.

For full-field medium-depth peeling: in 15 patients with dark complexions treated with Jessner’s followed by 35% TCA, transient post-inflammatory hyperpigmentation affected most patients. All were free of noticeable pigmentation three months after the final peel, and the authors concluded the peel was safe and effective in dark complexions.^{[10]15 patients described only as having DARK COMPLEXIONS — the paper reports NO FITZPATRICK PHOTOTYPES at all — treated with Jessner's solution followed by 35% TCA, which is not 35% TCA alone. Transient post-inflammatory hyperpigmentation affected the majority; the reported 'nine patients (73.4%)' is internally inconsistent, since 9 of 15 is 60%. All were free of noticeable pigmentation three months after the final peel, and the authors concluded the peel was safe and effective in dark complexions. Quote it as 'most patients', and do not use it to answer a question about a named phototype.Directly tested by the source[10] Al-Waiz MM, Al-Sharqi AI. Medium-depth chemical peels in the treatment of acne scars in dark-skinned individuals. Dermatol Surg. 2002 May;28(5):383-387.Tier 3}

We are saying “most” rather than a percentage deliberately: the paper reports “nine patients (73.4%)”, and 9 of 15 is 60%, not 73.4%. The figure is internally inconsistent, so quoting it precisely would be quoting an error.

For focal CROSS: it was developed entirely in Fitzpatrick IV–V patients, and a later review describes it as well tolerated in phototypes I–V. But no source directly compares the two techniques in darker skin, so treating CROSS as the safer option is a reasonable inference rather than a finding — and nothing we located covers phototype VI at all.^{[3, 7, 1]iThe published Fitzpatrick IV+ caution is stated for full-field medium-depth peeling. Focal CROSS was developed entirely in Fitzpatrick IV-V patients and a later review describes it as well tolerated in phototypes I-V — but no source directly compares the two techniques in darker skin, so treating CROSS as the safer option in skin of colour is an inference, not a finding, and no source located covers phototype VI.Inferred from adjacent evidence[3] Lee JB, Chung WG, Kwahck H, Lee KH. Focal treatment of acne scars with trichloroacetic acid: chemical reconstruction of skin scars method. Dermatol Surg. 2002 Nov;28(11):1017-1021.Tier 3[7] Chung HJ, Al Janahi S, Cho SB, Chang YC. Chemical reconstruction of skin scars (CROSS) method for atrophic scars: A comprehensive review. J Cosmet Dermatol. 2021 Jan;20(1):18-27.Tier 4[1] Lee KC, Wambier CG, Soon SL, Sterling JB, Landau M, Rullan P, Brody HJ; International Peeling Society. Basic chemical peeling: superficial and medium-depth peels. Journal of the American Academy of Dermatology. 2019;81(2):313–324. doi:10.1016/j.jaad.2018.10.079Tier 4}

The defensible position: PIH after medium-depth TCA in darker skin is common and, on the one prospective series, transient. That is a risk to counsel and mitigate rather than an absolute bar — while noting that our chemical peel entry carries the International Peeling Society’s firmer line that medium-depth peels are not recommended in phototypes IV and above. Both positions are in the literature.

Two uses that circulate with the wrong number attached.

Incomplete earlobe clefts have been repaired non-surgically with TCA 90% — not 100% — in 32 patients across 53 earlobes, taking on average 15 days from first to last application, with all clefts repaired and no recurrence at one year.^{[8, 1]Incomplete earlobe clefts have been repaired non-surgically with TCA 90% — not 100% — in 32 patients across 53 earlobes, taking on average 15 days from first to last application, with all clefts repaired and no recurrence at one year.Directly tested by the source[8] de Mendonça MC, de Oliveira AR, Araújo JM, Silva Md, Gamonal A. Nonsurgical technique for incomplete earlobe cleft repair. Dermatol Surg. 2009 Mar;35(3):446-450.Tier 3[1] Lee KC, Wambier CG, Soon SL, Sterling JB, Landau M, Rullan P, Brody HJ; International Peeling Society. Basic chemical peeling: superficial and medium-depth peels. Journal of the American Academy of Dermatology. 2019;81(2):313–324. doi:10.1016/j.jaad.2018.10.079Tier 4}

Rhinophyma: the technique paper the dermatology literature actually cites applies 70% or 90% TCA to hypertrophic areas only, until intense local whitening appears, leaving normal and atrophic skin untouched, with thick dark crusts for seven to ten days. The same paper uses 35% in a single pass for the very mild lesions it says are common in female patients.^{[9, 1]For rhinophyma, the technique paper cited in the dermatology literature applies 70% or 90% TCA to hypertrophic areas only, until intense local whitening appears, leaving normal and atrophic skin untouched, with thick dark crusts for 7-10 days. The same paper specifies a lower concentration — 35% in a single pass — for the very mild lesions it says are common in female patients, and applies the method across the full range of severity, using two or more passes on very hypertrophic lesions.Directly tested by the source[9] Gaspar NK, Gaspar APA, Aidê MK. Rhinophyma: practical and safe treatment with trichloroacetic acid. Surg Cosmet Dermatol. 2014;6(4):368-372.Tier 4[1] Lee KC, Wambier CG, Soon SL, Sterling JB, Landau M, Rullan P, Brody HJ; International Peeling Society. Basic chemical peeling: superficial and medium-depth peels. Journal of the American Academy of Dermatology. 2019;81(2):313–324. doi:10.1016/j.jaad.2018.10.079Tier 4}

That indication rests on an uncontrolled technique report with no patient count, no follow-up protocol and no outcome measure— and its claim of five decades of use without adverse effects cannot be verified.^{[9]The rhinophyma indication rests on an uncontrolled technique report with no patient count, no follow-up protocol and no outcome measure — its claim of five decades of use without adverse effects cannot be verified.Directly tested by the source[9] Gaspar NK, Gaspar APA, Aidê MK. Rhinophyma: practical and safe treatment with trichloroacetic acid. Surg Cosmet Dermatol. 2014;6(4):368-372.Tier 4}

Both are medical procedures on structures a skincare professional should not be treating. They are here because the concentrations attached to them circulate widely and are wrong.

The systematic review evidence covers only five prospective trials and 210 patients, at concentrations of 15–35% — and provides no evidence at all for concentrations above 35% or for any focal technique.^{[11]The systematic review evidence for TCA in photoaging covers only five prospective trials and 210 patients at concentrations of 15-35%, and provides no evidence at all for concentrations above 35% or for any focal technique.Directly tested by the source[11] S Sitohang IB, Legiawati L, Suseno LS, Safira FD. Trichloroacetic Acid Peeling for Treating Photoaging: A Systematic Review. Dermatol Res Pract. 2021 Aug 30;2021:3085670.Tier 1}

So if you are quoting photoageing evidence to justify a stronger peel than 35%, or to justify CROSS, you are quoting outside the dataset.

No national licensing scheme is in force in England. The power to create one sits in section 180 of the Health and Care Act 2022, in force since 1 July 2022 and never exercised.^{[13]No NATIONAL licensing scheme is in force IN ENGLAND. The August 2025 government response does not assign individual procedures to tiers: it says the consultation 'has been helpful in identifying and suggesting where further work or review is needed to better understand these risks', commits to a further public consultation 'to be launched early next year', and states the finalised scheme 'will be subject to Parliamentary debate before implementation'. The power sits in section 180 of the Health and Care Act 2022, in force since 1 July 2022 but never exercised. IMPORTANT: none of that displaces EXISTING LOCAL special-treatment licensing, which may still apply and must be checked with your council — and Scotland, Wales and Northern Ireland have separate regimes that cannot be inferred from an England consultation.Directly tested by the source[13] Department of Health and Social Care. The licensing of non-surgical cosmetic procedures in England: consultation response. GOV.UK, published 7 August 2025.Tier 1}

Two things that does not mean, and this section previously implied both. It does not mean nothing licenses you: existing local special-treatment licensing may still apply and is a question for your council. And it is an England position — Scotland has legislated separately, and Wales and Northern Ireland have their own regimes that cannot be inferred from an England consultation.

England’s 2023 consultation proposedplacing peels destroying only into viable epidermis in green, medium-depth peels destroying full epidermis into upper dermis in amber, and deeper peels such as phenol in red — and its annex states that medium-depth peels “are usually carried out using trichloroacetic acid (TCA) at concentrations between 35% and 50%”.^{[12]England's 2023 consultation PROPOSED placing peels that destroy only into viable epidermis in the green tier, medium-depth peels destroying the full epidermis into the upper dermis in amber, and deeper peels such as phenol in red — and its annex states medium-depth peels 'are usually carried out using trichloroacetic acid (TCA) at concentrations between 35% and 50%'.Directly tested by the source[12] Department of Health and Social Care. The licensing of non-surgical cosmetic procedures in England: consultation document. GOV.UK; opened 2 September 2023, closed 28 October 2023.Tier 1}

The August 2025 government response did not assign individual procedures to tiers. It committed to a further public consultation and confirmed the finalised scheme will be subject to Parliamentary debate before implementation.

On the JCCP’s voluntary register, peels sit within “Skin Rejuvenation – Micro Needling and Peels”. The register does not stratify peels by depth or TCA concentration, and confers no licence.^{[14]On the JCCP's voluntary register, chemical peels sit within one of five modalities, 'Skin Rejuvenation – Micro Needling and Peels'; the register does not stratify peels by depth or TCA concentration and confers no licence.Directly tested by the source[14] Joint Council for Cosmetic Practitioners (JCCP). Treatments [register modalities]. jccp.org.uk, accessed 1 August 2026.Tier 4}

We looked for a UK instrument capping the concentration of TCA usable in a cosmetic procedure and found none.^{[no source found]No UK regulatory instrument was found that caps the concentration of trichloroacetic acid that may be used in a cosmetic procedure. That absence is not permission: jurisdiction, local special-treatment licensing, intended treatment depth, professional scope, general product and chemical-safety duties, supplier instructions and insurance may all constrain the procedure, and this entry previously listed only four of those as though the list were exhaustive.We looked and found no source either way}

• Do not dilute a “100%” stock to working strength. That method produced the strongest solution of the four tested — it is the practice the literature warns against, not a shortcut.
• Ask your supplier for the basis of the percentage. Weight-to-volume is the standard, and “grams into 100 mL of water” is a different, weaker solution.
• Treat the depth table as consent guidance, not as a measured guarantee.
• Read frost as vigour, not as depth. No level has been validated against a measured histology.
• Consider 70% for CROSS where either would do. No efficacy difference was detected against 100%, significantly shorter crusting.
• Wait five minutes before assessing the endpoint or applying more. TCA penetrates slowly and overcoating is the risk the advice guards against — expert guidance citing a textbook, not a validated timing study.^{[1]The review advises waiting at least five minutes before assessing the frosting endpoint or applying more, because TCA penetrates slowly and overcoating is the risk. That sentence cites a textbook, so it is expert guidance rather than a validated timing study — and the review does not call overcoating the commonest technical error.Directly tested by the source[1] Lee KC, Wambier CG, Soon SL, Sterling JB, Landau M, Rullan P, Brody HJ; International Peeling Society. Basic chemical peeling: superficial and medium-depth peels. Journal of the American Academy of Dermatology. 2019;81(2):313–324. doi:10.1016/j.jaad.2018.10.079Tier 4}
• Counsel PIH explicitly in darker skin — common after medium-depth peeling, and transient in the one prospective series.

• The depth-by-concentration relationship itself, which has never been measured against histology in human skin.
• What any given frost level corresponds to anatomically.
• Whether CROSS is genuinely safer than full-field peeling in darker skin. Plausible, never compared directly, and untested in phototype VI.
• How CROSS compares with needling and PRP. The one three-arm trial reports no head-to-head test, and secondary accounts of it conflict.
• Anything above 35% for photoageing, and any focal technique for it — outside the systematic review’s dataset entirely.
• Whether the rhinophyma technique works, on any measured outcome.

“Just dilute the 100% down to working strength.”

“Weight-to-volume just means grams into 100 mL of water.”

“Level III frost means upper reticular dermis.”

“CROSS is unsafe in skin of colour.”

“Earlobe clefts and rhinophyma use 100% TCA.”

“The green/amber/red tiers are the law now.”

Can I make up my own TCA solution?

What strength for CROSS?

Which scars respond?

Is 35% TCA safe on a Fitzpatrick V client?

Is there a legal maximum concentration in the UK?

Each source is graded by evidence tier. Tier 4 material (manufacturer documents, expert consensus, practitioner experience) is useful for protocol and context, and is never presented as equivalent to independent clinical evidence.

1. Lee KC, Wambier CG, Soon SL, Sterling JB, Landau M, Rullan P, Brody HJ; International Peeling Society. Basic chemical peeling: superficial and medium-depth peels. Journal of the American Academy of Dermatology. 2019;81(2):313–324. doi:10.1016/j.jaad.2018.10.079Tier 4Supports: CME narrative review, not a systematic review. Table I "Depth of penetration of trichloroacetic acid chemical peels" gives verbatim: TCA 10-15% = "Epidermis"; 15-30% = "Epidermis"; 35% = "Superficial papillary dermis"; 50-100% = "Approaching and reaching upper reticular dermis with increased risk of complications; appropriate for focal use only". The table cites a book chapter (Wambier C, Brody H. Classification of chemical peels. In: da Costa A, ed. Minimally Invasive Aesthetic Procedures for Dermatologists and Plastic Surgeons. Springer Nature; 2019:1-12) — no primary histology is cited for the table. Text states: "The currently accepted standard preparation of TCA is weight to volume. Other preparation methods, such as weight to weight, grams of TCA per 100 mL water, and 100% TCA diluted to lower percentages can result in increased TCA concentrations and complications." Also: "Depth of penetration correlates directly to concentration"; "TCA >35% is used for focal treatment of individual lesions because pigmentary complications and scars are common with use over large areas"; "TCA penetrates slowly, so one must wait at least 5 minutes to assess the frosting endpoint and to avoid overcoating"; "There are 3 levels of frosting: 1) a light reticular frost with background erythema, 2) a confluent light white frost with background erythema, and 3) a solid white frosting without erythema"; "Frosting seen with TCA corresponds to epidermal and dermal protein denaturation" (no per-level histological depth is given); "TCA >80% is only appropriate for focal use" with the listed focal examples being mild-to-moderate rhinophyma, CROSS, earlobe tears ("TCA 90%") and xanthelasma (macular 50%, papular 70-100%). Note internal inconsistency: body text says earlobe tears are treated with "TCA 90%" while the Fig 2 legend reads "Earlobe cleft treated with 2 sessions of 100% trichloroacetic acid administered 1 month apart." Medium-depth key points state: "TCA 50% risks scarring and dyspigmentation"; "Historically, medium-depth peels were performed using TCA 50%, yielding uneven penetration and erosions, PIH, and scars", prompting Brody, Monheit and Coleman to add a physical/chemical epidermolysis step before TCA 35% "and thereby allow for its safe, predictable, even penetration". Also: "Medium-depth peels should not be used elsewhere than on the face or the scalp because of the risk of scarring" and "Medium-depth peels are not recommended for Fitzpatrick skin phototypes >=IV because of the risk of PIH" (cited to Brody's textbook), with risk "reduced by prepeel preparation with hydroquinone for 1 month and peeling during the winter season". Fig 1 legend defines the three frost levels clinically only.Funding / interest: Stated in the paper: "Funding sources: None." and "Conflicts of interest: None declared." Authored under the banner of the International Peeling Society, a professional body promoting peeling; author affiliations are academic dermatology departments (Brown, Yale, Scripps, Wolfson, UCSD, Emory).
2. Bridenstine JB, Dolezal JF. Standardizing chemical peel solution formulations to avoid mishaps. Great fluctuations in actual concentrations of trichloroacetic acid. J Dermatol Surg Oncol. 1994 Dec;20(12):813-816.Tier 3Supports: Laboratory comparison, not a clinical study. Determined actual TCA concentration under four preparation methods, all converted to the pharmaceutical weight-to-volume (wt/vol) standard: "Method I was wt/vol, method II was weight to weight (wt/wt), method III was grams of TCA added to 100 cc water, and method IV was the usage of saturated TCA, and calling it 100%, then making appropriate dilutions." Result, verbatim: "The relative concentrations of TCA, ranked by the wt/vol pharmaceutical standard, showed that from strongest to weakest: method IV > method II > method I > method III." Conclusion: "Tremendous variations were found in the relative concentrations of TCA in these solutions. To avoid mishaps and complications, the wt/vol method should be used." Scope limit: the abstract reports the rank order but not the numeric percentage deviation for each method; the full text was not retrieved. Critically, method IV — diluting a saturated solution called "100%" — was the STRONGEST, and method III — grams added to 100 cc of water — was the WEAKEST, i.e. weaker than true w/v.Funding / interest: The publisher discloses that Dr James F. Dolezal had a FINANCIAL INTEREST IN DELASCO, a supplier of TCA preparations — and Delasco markets Modified Jessner's. No separate funding statement was located. A supplier interest in a paper recommending one preparation standard is material provenance.
3. Lee JB, Chung WG, Kwahck H, Lee KH. Focal treatment of acne scars with trichloroacetic acid: chemical reconstruction of skin scars method. Dermatol Surg. 2002 Nov;28(11):1017-1021.Tier 3Supports: The founding CROSS paper. Retrospective analysis of 65 patients with atrophic acne scars treated between July 1996 and July 2001. "Thirty-three patients were treated with 65% TCA CROSS and 32 patients were treated with 100% TCA CROSS. All patients had Fitzpatrick skin types IV-V." Technique defined as "the focal application of higher trichloroacetic acid (TCA) concentrations by pressing hard on the entire depressed area of atrophic acne scars". Results: "27 of 33 patients (82%) (the 65% TCA group) and 30 of 32 patients (94%) (the 100% TCA group) experienced a good clinical response. All patients in the 100% TCA group who received five or six courses of treatment showed excellent results." "There were no cases of significant complication." Scope limits: retrospective, no control group, no blinding, subjective response grading, single-centre, Korean population, Fitzpatrick IV-V only. It does not establish safety of full-field TCA at these concentrations — application was focal.Funding / interest: No funding or conflict statement in the PubMed record. Authors from Leejiham Skin Clinic and Department of Dermatology, Yonsei University College of Medicine, Seoul, Korea — a private clinic plus academic department; the technique is the authors' own, which is an intellectual interest.
4. Yug A, Lane JE, Howard MS, Kent DE. Histologic study of depressed acne scars treated with serial high-concentration (95%) trichloroacetic acid. Dermatol Surg. 2006 Aug;32(8):985-990.Tier 3Supports: The only human histological evidence located for CROSS. "Acne scars in three patients were treated with focal 95% TCA by serial application. Wooden applicators were used to apply TCA focally and repeated at 6-week intervals for a total of six treatments. Punch biopsies were performed at baseline and at 1 year postoperatively." Staining: haematoxylin/eosin, Masson trichrome, Verhoeff-van Gieson. Results: "Histologic examination demonstrated a decrease in the depth of acne scars. In addition, increased collagen fibers and fragmentation of elastic fibers were noted. There were no complications from the procedure." Scope limits: n=3, uncontrolled, unblinded, no quantitative morphometry reported in the abstract, and the concentration studied (95%) is not the 65%/70%/100% used in the comparative trials. Note the finding of elastic fibre FRAGMENTATION is not unambiguously desirable and is reported alongside the collagen increase.Funding / interest: No funding or conflict statement in the PubMed record. Authors from Mercer University School of Medicine, Macon, Georgia, USA.
5. Nofal E, Helmy A, Nofal A, Alakad R, Nasr M. Platelet-rich plasma versus CROSS technique with 100% trichloroacetic acid versus combined skin needling and platelet rich plasma in the treatment of atrophic acne scars: a comparative study. Dermatol Surg. 2014 Aug;40(8):864-873.Tier 2Supports: "Forty-five patients with atrophic acne scars were randomly assigned to 3 equal groups; Group A received intradermal injection of PRP, Group B received chemical reconstruction of skin scars technique with TCA 100%, and Group C was treated by combined skin needling and PRP. Each patient underwent 3 sessions at 2-week interval." Results: "All the patients completed the study. The 3 groups showed statistically highly significant improvement in the degree of acne scars after treatment (p < .001). No major adverse effects were observed in the studied groups." Scope limits: n=15 per arm, no untreated or sham control, only 3 sessions (fewer than the 5-6 associated with best results in Lee 2002), short follow-up, Egyptian population with skin types not stated in the abstract. The abstract reports within-group improvement but does not report a statistically significant difference BETWEEN the three modalities, so it does not establish superiority of CROSS over PRP or needling.Funding / interest: No funding or conflict statement in the PubMed record. All authors affiliated with the Dermatology Department, Faculty of Medicine, Zagazig University, Egypt.
6. Soysal MÇ, Akçalı C. Comparison of 70% and 100% concentration of trichloroacetic acid peeling efficacy with chemical reconstruction of skin scars technique in atrophic acne scar treatment. Arch Dermatol Res. 2025 Mar 12;317(1):547.Tier 2Supports: Most recent randomised head-to-head on CROSS concentration. "A total of 40 patients were randomly assigned to two equal groups of 20: the first group received 70% TCA, while the second group was treated with 100% TCA." Mean age 27.07 ± 5.48 years (70% group) and 23.5 ± 2.9 years (100% group). Results: "No significant differences were observed between post-treatment scores provided by patients and researchers... However, within the 100% TCA group, treatment efficacy was significantly greater for icepick scars than for boxcar scars. Additionally, crusting durations were significantly prolonged in the 100% TCA group." Conclusion: "No significant differences in overall efficacy were observed between the two treatment groups. Notably, the crusting time following the procedure was longer in the group treated with 100% TCA." Scope limits: n=20 per arm, Turkish population, Fitzpatrick types not stated in the abstract, no long-term follow-up reported. The icepick-versus-boxcar finding is a within-group comparison in the 100% arm, not a between-arm result.Funding / interest: Stated: "Declarations. Competing interests: The authors declare no competing interests." Authors from Nizip State Hospital Dermatology Clinic and Gaziantep University Hospital, Turkey.
7. Chung HJ, Al Janahi S, Cho SB, Chang YC. Chemical reconstruction of skin scars (CROSS) method for atrophic scars: A comprehensive review. J Cosmet Dermatol. 2021 Jan;20(1):18-27.Tier 4Supports: Self-described "comprehensive review", not a systematic review — "An extensive literature review was conducted to identify articles relating to CROSS method for atrophic scars from 2002 to 2018" with no stated PRISMA methodology. "The literature search yielded 19 articles meeting criteria. CROSS method has been used for the treatment of acne scars, varicella scars, enlarged pores, and depressed surgical scars. In studies using the quantile grading scale for acne scars, 60%-100% of patients showed >25% improvement. In two studies for varicella scars, 83%-100% of patients showed >25% improvement. CROSS method seems to be effective specifically for ice-pick scars. It is well tolerated and safe in Fitzpatrick skin phototypes I-V. Most reported complications are temporary and include postinflammatory dyspigmentation, erythema, pain, pruritus, infection, and widening of scars." Authors' own stated limitations, verbatim: "current published works have several limitations, including small sample sizes, lack of control group, different concentrations of acid, different frequency of treatments, and follow-up periods. Larger, randomized, controlled studies are needed to elucidate the optimal treatment protocol of CROSS method." They also state "no standardized treatment guideline exists for CROSS method". Note the safety claim covers phototypes I-V, not VI; and "widening of scars" is a listed complication of the technique itself.Funding / interest: No funding or conflict statement in the PubMed record. Authors from Beth Israel Deaconess Medical Center, Boston University, Yonsei Seran Dermatology and Laser Clinic (Seoul), and Union Square Laser Dermatology (New York) — two private cosmetic clinics among four affiliations.
8. de Mendonça MC, de Oliveira AR, Araújo JM, Silva Md, Gamonal A. Nonsurgical technique for incomplete earlobe cleft repair. Dermatol Surg. 2009 Mar;35(3):446-450.Tier 3Supports: The primary clinical series behind the earlobe-cleft indication, and it uses 90%, not 100%: "We present a nonsurgical procedure for incomplete earlobe cleft repair using trichloroacetic acid 90%." "We assessed 32 patients with a total of 53 earlobes to be noninvasively repaired." Results: "Complete treatment varied from 2 to 50 days, an average of 15 days between the first and last application of trichloroacetic acid 90%. No recurrences were observed during 1 year of follow-up. All of the clefts were totally repaired, and all of the patients were satisfied with the aesthetic results." Scope limits: single-arm, uncontrolled, unblinded, no comparison against surgical repair, INCOMPLETE clefts only (not complete/through-and-through clefts), single centre, 1-year follow-up. Patient satisfaction assessed without a validated instrument.Funding / interest: No funding or conflict statement in the PubMed record. Authors from the Department of Dermatology, College of Medicine, Federal University of Juiz de Fora, Minas Gerais, Brazil.
9. Gaspar NK, Gaspar APA, Aidê MK. Rhinophyma: practical and safe treatment with trichloroacetic acid. Surg Cosmet Dermatol. 2014;6(4):368-372.Tier 4Supports: Technique description, NOT a study — there is no patient count, no denominator, no follow-up protocol and no outcome measurement. Verbatim abstract: "The authors introduce a method for the treatment of different intensities and scales of rhinophyma, with trichloroacetic acid. This is a safe process, created and performed by the authors for five decades, with an absence of descriptions of adverse effects." The method text specifies 70% or 90% TCA, not 100%: "The procedure begins with removing all grease from the skin, using acetone immediately before, then evolving to the application of 70% or 90% trichloroacetic acid (TCA) with a stick wrapped in cotton (forming a flat swab) up until the total and intense local whitening of the area occurs, which happens a few seconds after the application." "In very exuberant and hypertrophic lesions, the application must be more intense (2 or more times in a row)." "The areas of normal skin or containing atrophic lesions should always be left untouched." Stated contraindication: "This process is not indicated for the few patients with scarring and a xerotic and whitish appearance." Aftercare: crusts "will remain for 7 to 10 days"; oral aciclovir for patients with herpes simplex history; tetracycline and ibuprofen where inflammation is intense. Claim of "countless patients without any complications" is unquantified and unverifiable. This is the source cited by the JAAD review for its rhinophyma statement.Funding / interest: Stated on the article page: "Financial support: None. Conflict of interest: None." Published in the New Techniques (Novas Técnicas) section of a Brazilian society journal. The method is the first author's own, developed by Gaspar NK — an intellectual interest in its favourable presentation.
10. Al-Waiz MM, Al-Sharqi AI. Medium-depth chemical peels in the treatment of acne scars in dark-skinned individuals. Dermatol Surg. 2002 May;28(5):383-387.Tier 3Supports: The counterweight to the blanket 'avoid medium depth in darker skin' rule. "A total of 15 patients (14 women and 1 man) were seen between November 1998 and March 2000... The peel was performed using a combination of Jessner's solution followed by the application of 35% trichloroacetic acid (TCA). The mean age of patients who entered the study was 28 years. A total of 42 peeling sessions were performed: 13 patients had the full three-session regiment, 1 patient had two sessions, and 1 had only one session." Results: "Significant improvement (greater than 75% clearance of lesions) occurred in 1 patient (6.6%), moderate improvement (51-75% clearance) in 8 patients (53.3%), mild improvement (26-50% clearance) in 4 patients (26.6%), minimal improvement (1-25% clearance) in 1 patient (6.6%), and no response in 1 patient (6.6%)." Adverse events: "Nine patients (73.4%) suffered from transient postinflammatory hyperpigmentation. In two of them it was preceded by erythema that lasted for more than 1 month. All patients were free of noticeable pigmentation 3 months after the final peel. Patients in whom hyperpigmentation did not develop were of light brown complexion." On scar morphology: "Four patients (26.6%) had mainly pitted scars and deep atrophic scars. The clinical response in those patients was moderate, mild, minimal, and no response, respectively" — i.e. ice-pick/deep scars responded worst to full-field medium depth. Authors' conclusion: "medium-depth chemical peel is a safe and effective method of treating acne scars even in patients with dark complexion." Scope limits: n=15, uncontrolled, unblinded, Iraqi population described as "dark-skinned"/"dark complexion" with FITZPATRICK PHOTOTYPES NEVER STATED, so this cannot be read as a clean Fitzpatrick IV-VI dataset; follow-up 3 months after final peel.Funding / interest: No funding or conflict statement in the PubMed record. Authors from the Department of Dermatology, Baghdad University, Iraq.
11. S Sitohang IB, Legiawati L, Suseno LS, Safira FD. Trichloroacetic Acid Peeling for Treating Photoaging: A Systematic Review. Dermatol Res Pract. 2021 Aug 30;2021:3085670.Tier 1Supports: Systematic review of prospective trials searched across PubMed, MEDLINE, EMBASE, Cochrane and Scopus on 2 November 2020. Yield: "Five studies included three randomized comparison studies and two prospective cohort studies", totalling 210 patients, with TCA concentrations ranging 15%-35% as monotherapy or combination. Outcome instruments across studies included Cutometer SEM 474 (elasticity), Mexameter MX 18 (melanin/erythema index), Global Aesthetic Improvement Scale and Physician Global Assessment. Findings: "These studies show that TCA peeling significantly improve the cosmesis of photoaged facial skin. Low concentration is effective for superficial sun damage. Medium-depth peels using a higher concentration of TCA or as combination therapy are effective as skin resurfacing agents to reduce wrinkles. Some adverse effects may occur but usually resolve within weeks." Reported adverse events were immediate burning/stinging, erythema and scaling typically resolving within a week, with rare scarring, hypopigmentation and bacterial superinfection. Authors' stated limitations: "An equivalent basic skin preparation such as topical retinoic acid skin priming prior to intervention is necessary for more objective comparison. Further research studies with a larger sample size and longer follow-up period are required." Critical scope limit: the review covers ONLY 15%-35% TCA for photoaging. It provides no evidence for 50%-100% TCA, for CROSS, or for any focal indication, and no pooled meta-analytic effect size was produced.Funding / interest: Funded by Universitas Indonesia. Stated: "The authors declare that there are no conflicts of interest regarding the publication of this paper." Authors from the Division of Cosmetic Dermatology, Universitas Indonesia / Dr. Cipto Mangunkusumo Hospital, Jakarta.
12. Department of Health and Social Care. The licensing of non-surgical cosmetic procedures in England: consultation document. GOV.UK; opened 2 September 2023, closed 28 October 2023.Tier 1Supports: A CONSULTATION PROPOSAL, not law. Sets out a green/amber/red model and asks respondents "whether any of the suggested procedures should be moved to another category (green, amber or red)". Green is defined as "procedures with the lowest risk of complications" where "All practitioners are eligible to perform licensed procedures where they meet agreed standards", and the proposed green list includes "chemical peels that involve destruction only into viable epidermis (the outermost layer of the skin)" alongside microneedling, mesotherapy, IPL/LED and micropigmentation. The proposed amber list includes "medium depth peels that involve full thickness destruction of entire epidermis into upper dermis (the inner layer of the 2 main layers of the skin)". The proposed red list — restricted to "qualified and regulated healthcare professionals working out of CQC registered premises" and excluded from local authority licensing — includes "deeper chemical peels such as phenol peels". Annex A gives the depth definitions verbatim: "There are 3 types of peels: superficial, medium and deep"; superficial peels "where skin cells are removed from the epidermis, are included under the green category" with acids "lactic, glycolic and tartaric acid"; "medium depth peels, involving full thickness destruction of entire epidermis into the upper dermis... are included under the amber category. The acids used in these peels are able to penetrate the epidermis and the upper dermis. These peels are usually carried out using trichloroacetic acid (TCA) at concentrations between 35% and 50%. Other acids are sometimes used, including glycolic, pyruvic and salicylic acid"; and "deep chemical peels using phenol or otherwise intended for use at the level of the reticular dermis (the thick bottom layer of the dermis)". The consultation notes the power derives from the Health and Care Act 2022, which "gave the Secretary of State for Health and Social Care the power to introduce a licensing regime". This is the only UK government document located that names a TCA concentration range.
13. Department of Health and Social Care. The licensing of non-surgical cosmetic procedures in England: consultation response. GOV.UK, published 7 August 2025.Tier 1Supports: "The consultation received over 11,800 responses, with the majority agreeing with the proposals put forward in the consultation." The government commits to three strands: "introduce legal restrictions which will ensure that cosmetic procedures which are deemed to pose the highest level of risk to the public (such as liquid Brazilian butt lifts) are classed as Care Quality Commission (CQC) regulated activities - which can only be performed by specified regulated healthcare professionals"; "develop and implement local authority licensing for lower risk procedures through powers granted through the Health and Care Act 2022"; and "introduce age restrictions for those undergoing non-surgical cosmetic procedures". Decisively, it does NOT assign individual procedures to tiers: "The consultation responses have been helpful in highlighting where further work is needed to determine specific procedures' classification within the scheme, and around the elements which will underpin the scheme. Further public consultation will take place to inform the government's plans in this space." Sequencing: "initial work will prioritise the introduction of restrictions for high-risk procedures" and "DHSC and CQC will work closely together in the coming months to detail how these restrictions will be put into effect. The proposed changes will be detailed in a public consultation, to be launched early next year." Legal status: "The proposals will be taken forward through secondary legislation and therefore subject to the Parliamentary process before the legal restrictions or licensing regulations can be introduced." No chemical peel or TCA concentration appears in the response's commitments.
14. Joint Council for Cosmetic Practitioners (JCCP). Treatments [register modalities]. jccp.org.uk, accessed 1 August 2026.Tier 4Supports: Confirms the five modalities covered by the JCCP register: "Botulinum Toxins", "Dermal Fillers", "Skin Rejuvenation – Micro Needling and Peels", "Lasers and Light (LIPLED)" and "Hair Restoration Surgery". Chemical peels therefore sit within the third modality, alongside microneedling. Scope limit: the JCCP is a voluntary register, not a statutory regulator; entry on it is not a legal requirement to perform peels in the UK and it confers no licence. The page does not stratify peels by depth or by TCA concentration.Funding / interest: The JCCP is a voluntary, non-statutory register funded by practitioner and education-provider registration fees, so it has a financial interest in the scope of its own modalities.
15. Wambier CG, Brody HJ. Classification of chemical peels. In: da Costa A, ed. Minimally Invasive Aesthetic Procedures for Dermatologists and Plastic Surgeons. Springer Nature; 2019:1–12.Tier 4Supports: PROVENANCE ONLY. This is the book chapter the JAAD review's depth-by-concentration table cites as its authority — written by two of that review's own authors. Registered separately so the table's provenance is inspectable, and so the chapter is not conflated with the JAAD article as it was in this entry until August 2026. No primary histology is cited for the table in either place.

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