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Wound-healing cascade

Also known as: wound healing, healing cascade, inflammatory phase

The wound-healing cascade is the overlapping sequence — haemostasis, inflammation, proliferation and remodelling — by which skin repairs injury. Controlled activation of it underpins microneedling, resurfacing and peels. The phases overlap rather than following one another in blocks.

Evidence status

Strong

The phases, their cellular sequence and the long remodelling tail are established textbook physiology, corroborated by human wound biopsy work. The clinical modifiers are more mixed: the smoking data are strong but surgical rather than aesthetic, the corticosteroid guidance is a narrative review, and the post-procedure steroid question rests on one mouse study.

What it is#

The wound-healing cascade is the sequence by which skin repairs injury: haemostasis, inflammation, proliferation and remodelling. Every needling, peel and resurfacing protocol is a deliberate, controlled attempt to start it.

Which is why the timings matter to a practitioner in a way they do not matter to most people. If you are creating injury on purpose, you are responsible for knowing what happens next and how long it takes.

The four phases#

The single most important thing to understand about them is that they overlap. They are not four boxes that close in turn.[1, 2]

  • Haemostasis. Immediate. Vasoconstriction, platelet aggregation, a fibrin clot that also acts as the provisional matrix cells will migrate through.
  • Inflammation. Neutrophils first, then macrophages — debridement, defence, and the signalling that recruits everything that follows.
  • Proliferation. Angiogenesis, granulation tissue, re-epithelialisation, and fibroblasts laying down new matrix. This is the phase treatments are aiming at.
  • Remodelling. The long one. Collagen III is gradually replaced by collagen I, cross-linking matures, and the tissue slowly gains strength.

Write “proliferation: days 3–10” on a client aftercare sheet if you like, but know that you are drawing a hard border on something that does not have one.

The timeline#

The numbers below are the ones worth committing to memory, because they are the ones clients ask about.

  • Up to ~10 minutes. Local vasoconstriction, before vasodilatation takes over.[1]
  • Within 24 hours. Neutrophils are recruited, and stay for roughly two to five days.[1]
  • Around day 3. Macrophages arrive and take over phagocytosis.[1]
  • Days 3–10. The proliferative phase, which may take days or weeks to complete.[1, 2]
  • Days 5–7. Fibroblasts have begun laying down new collagen and glycosaminoglycans.[2]
  • Week 3 to 12 months.Remodelling — which overlaps everything above rather than following it. These are descriptions of what tissue is doing, not a treatment calendar.[1, 2]
  • 11–14 weeks. Maximal tensile strength of an incision wound.[1, 2]

Two qualifications travel with that list. The days 5–7 figure is when collagen deposition starts, not when it is done — the source says fibroblasts “have started to”. And the 11–14 week figure is for an incision wound; the source does not generalise it to every wound type, and a fractional injury field is not an incision.

The long tail#

This is the part that gets left out, and it is the part that changes how you talk to a client about their result.

In human excisional wounds, the proportion of collagen III relative to collagen I rose over the first six weeks and was still about 70% above baseline at six months. Over the same period, pepsin extractability of collagen from wound biopsies rose from 32.8% (±6.8) to 89.1% (±8.9), with a matching fall in the mature cross-link.[3]

In plain terms: half a year after wounding, the tissue is still made of the wrong collagen, and what is there is still soft, immature and poorly cross-linked. The wound looked closed months earlier.

And it never entirely catches up. From about three months, a mature scar reaches only around 80% of the tensile strength of the original tissue.[1, 2]

Which is the honest answer to “when will I see the final result?” — later than most protocols imply, and the tissue is still changing after you have stopped taking photographs of it.

When it stalls#

A wound that fails to progress through the phases in an orderly way is called chronic. Where exactly that line sits is less settled than the term implies: one StatPearls chapter takes wounds to heal generally in four to six weeks and calls those that do not chronic, while the more recently updated chapter uses four weeks.[1, 2]

For an aesthetic practitioner the threshold is largely academic — a treatment site that is not clearly resolving at two weeks is already a conversation with a prescriber, not a waiting game. But it is worth knowing that the number varies, so you do not quote one as though it were a diagnostic criterion.

Smoking#

The strongest modifier in this entry, and the one most often waved at without numbers.

A meta-analysis of 140 cohort studies covering 479,150 patients found that smokers had roughly three and a half times the odds of tissue necrosis (adjusted OR 3.60, 95% CI 2.62–4.93), twice the odds of delayed healing or dehiscence (2.07, 1.53–2.81), twice the odds of wound complications overall (2.27, 1.82–2.84), and close to double the odds of surgical site infection (1.79, 1.57–2.04).[4]

Read the population carefully. These are surgical outcomes — flaps, incisions, implants — not microneedling or peels. It is reasonable to expect the direction to hold in aesthetic work, and unreasonable to quote these odds ratios as though they had been measured after a facial.

Does stopping before treatment help?

Less cleanly than you would hope. Across four randomised trials, perioperative smoking cessation reduced surgical site infections (OR 0.43, 95% CI 0.21–0.85) but showed no significant reductionin other healing complications (OR 0.51, 95% CI 0.22–1.19).[4]

That second confidence interval crosses 1. It should be reported as “no effect demonstrated”, not as a 49% reduction — and the whole finding rests on four trials.

Corticosteroids#

A client on steroids is not automatically a client you defer. The question is how long they have been on them.

Short courses of high-dose systemic corticosteroids lasting under ten days have no clinically important effect on wound healing. Use for at least 30 days before surgery may raise wound complication rates two to five fold, varying with dose, duration, comorbidity and the type of surgery.[5]

Keep the hedge. This is a narrative review of the human literature rather than a pooled analysis, and the range is wide because the underlying studies are heterogeneous. It is enough to justify asking the question at consultation and escalating to the prescriber where the answer is “months”.

The isotretinoin rule#

The six-month wait is one of the most confidently repeated rules in aesthetics, and one of the least well evidenced.

The 2017 systematic review put it plainly: the belief that isotretinoin taken within six to twelve months of cutaneous surgery contributes to abnormal scarring or delayed healing “is widely taught and practiced; however, it is based on 3 small case series from the mid-1980s”.[6]

The ASDS consensus that followed found insufficient evidence to justify delaying superficial chemical peels or non-ablative lasers — hair-removal lasers and lights, vascular lasers and non-ablative fractional devices — in patients currently or recently exposed to isotretinoin. It added, more tentatively, that superficial and focal dermabrasion may also be safe when performed by a well-trained clinician.[7]

What it did not clear

That list is closed, and the distinction matters more than the headline. Fully ablative laser and mechanical (rotary) dermabrasion are not recommended during systemic isotretinoin treatment — a negative stated explicitly in the companion systematic review. Skin surgery does not appear among the cleared procedures either.[6, 7]

Note the asymmetry: absence from a cleared list is not the same as a prohibition. Where the evidence genuinely says “do not”, we have cited the paper that says it.

And note what the “do not” actually covers. It is duringsystemic isotretinoin treatment. Neither source establishes a universal six-month wait after a course finishes, for any procedure. This page previously said the six-month rule “still stands” for ablative laser and mechanical dermabrasion; that was the folklore surviving inside the correction of the folklore.[6, 7]

One attribution worth getting right, because it circulates wrongly: the widely quoted “32 articles, 1,485 procedures” figure belongs to the JAMA Dermatology systematic review, not to the ASDS consensus paper, which contains no article or procedure count at all.

None of this is permission to needle someone mid-course on your own judgement. It is grounds to stop treating the six-month rule as settled science, and to route the decision to the prescribing clinician with the actual evidence in hand.

Steroids after a procedure#

A tempting shortcut — a topical steroid to take the redness out of a post-laser face. There is data on it, and it points somewhere specific.

In mice treated with ablative fractional CO2 laser, a single application of a medium-potency topical corticosteroid immediately afterwards suppressed the immediate redness with minimal disruption to healing. Dosing for two, three or five days delayed healing dose-dependently, with significantly larger crust area and epithelial gap at day nine.[8]i

The multi-dose groups also showed more myofibroblasts and more collagen at day 21 — which sounds like a bonus and is not. The authors read it as the steroid prolonging healing so that excess collagen accumulates, and it is unquantified histology from representative sections, with no cell counts and no p-values.[8]i

This is a mouse study. Six to seven animals per group, in mouse skin, with a laser protocol chosen for the model. It is not grounds for a human protocol, and non-prescribers should not be reaching for steroids at all. What it is good for is the shape of the risk: if a steroid has a place after ablative treatment, the evidence points to one dose rather than a course, and the harm from a course is the thing you were trying to avoid.

In professional practice#

  • Set expectations against the long tail, not the closure date. Skin that looks healed at two weeks is months from finished remodelling.
  • Space treatments against the phase you are targeting. Re-injuring skin still in early proliferation is not stacking a benefit.
  • Ask about smoking, and be specific about why. The effect size is real; the evidence is surgical. Say both.
  • Ask how long, not whether, on steroids — under ten days and thirty-plus days are different conversations — and then take it to their clinician. The perioperative literature describes dose- and duration-dependent effects; it does not clear anyone for anything.[5]
  • Do not apply the six-month isotretinoin rule reflexively — or override it yourself. Take it to the prescriber with the ASDS position.
  • Photograph late as well as early. A picture at three weeks is a picture of oedema and early granulation. Three months is a reasonable convention drawn from the remodelling biology, not a validated review point.[no source found]

What remains uncertain#

  • Whether the timings established for excisional and incisional wounds transfer cleanly to fractional injury fields, which heal from surrounding intact tissue rather than across a gap.
  • How much of the smoking effect seen in surgery carries into energy-based and needling procedures, where no comparable dataset exists.
  • Whether stopping smoking before an aesthetic procedure changes outcomes at all — the cessation trials measured surgical infection, and found nothing significant elsewhere.
  • Whether the single-dose post-laser steroid finding holds in human skin. It has not been tested there.
  • Where the safe interval genuinely sits after isotretinoin for ablative procedures, which the consensus did not clear and no adequately powered trial has defined.

Common misconceptions#

“The phases happen one after the other.”

They overlap. Proliferation runs while inflammation is still resolving, and remodelling begins before proliferation ends.[1, 2]

“Once it’s closed, it’s healed.”

Six months after wounding, collagen III was still about 70% above baseline and the new collagen was still poorly cross-linked.[3]

“Skin heals back to normal.”

A mature scar reaches about 80% of the original tissue’s tensile strength. It does not return to 100%.[1, 2]

“You must wait six months after isotretinoin, always.”

Not for superficial peels or non-ablative lasers, where the consensus found insufficient evidence to justify a delay.[7] And not, on this evidence, for anything else: what the review says is that ablative laser and mechanical dermabrasion are not recommended during treatment. It does not establish a universal six-month post-course interval.[6, 7]

“Any steroid course is a contraindication.”

Under ten days of high-dose systemic corticosteroid had no clinically important effect. Thirty days or more is the version that raises complication rates.[5]

Frequently asked questions#

How long should I leave between microneedling sessions?

We looked, and found no trial defining it.[no source found]Anyone quoting a number is quoting a protocol rather than evidence — including anyone deriving one from the healing phases, because phase biology describes what tissue is doing and does not validate a schedule. What the physiology supports is a direction: leave enough time for proliferation to run rather than re-injuring skin that is still in it.[1, 2]The interval itself has to come from the evidence and instructions for the exact device, and from how that client’s skin actually responded.

When are the final results visible?

Later than most aftercare sheets say. Remodelling runs from about week three for up to twelve months, and tensile strength peaks at eleven to fourteen weeks in an incision wound.[1, 2]

My client smokes. Do I refuse?

That is a clinical judgement for your indemnity and your protocols, not a rule this entry can set. What the evidence gives you is the size of the risk in surgical patients — roughly double the odds of delayed healing and dehiscence, more than triple for necrosis — and the honesty to say it is surgical data.[4]

Can I use hydrocortisone on post-treatment redness?

Not on your own initiative, and not as a course. The only relevant data is a mouse study, and in it repeated dosing delayed healing dose-dependently while a single dose did not.[8]i

Does the client need to be off isotretinoin before a peel?

For a superficial peel, the 2017 consensus found insufficient evidence to justify delaying it. That is a finding to take to the prescriber, not a decision to make around them.[7]

References#

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. Ozgok Kangal MK, Kopitnik NL. Physiology, Wound Healing. StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; updated 4 April 2025.Tier 4Supports: The cellular timings: vasoconstriction lasting up to about 10 minutes before vasodilatation; neutrophils recruited within 24 hours and remaining two to five days; macrophages arriving at about day three; proliferation from roughly day 3 to day 10 and taking days to weeks to complete; remodelling from day 21 to one year; mature scar reaching about 80% of original tensile strength. Uses a four-week threshold for a chronic wound.
  2. Wallace HA, Basehore BM, Zito PM. Wound Healing Phases. StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; updated 12 June 2023.Tier 4Supports: Fibroblasts have STARTED to lay down new collagen and glycosaminoglycans by days five to seven; maturation begins at around week three and can run up to twelve months; maximal tensile strength of an INCISION wound at about eleven to fourteen weeks; a mature scar reaching only about 80% of original tensile strength from about three months. Uses a four-to-six-week threshold for a chronic wound. This is the older of the two StatPearls wound-healing chapters.
  3. Robins SP, Milne G, Duncan A, Davies C, Butt R, Greiling D, James IT. Increased skin collagen extractability and proportions of collagen type III are not normalized after 6 months healing of human excisional wounds. Journal of Investigative Dermatology. 2003;121(2):267–272.Tier 3Supports: In human excisional wounds, the proportion of collagen III relative to collagen I rose over the first six weeks and was still about 70% above baseline at six months. Pepsin extractability of collagen from wound biopsies rose from 32.8% (±6.8) at baseline to 89.1% (±8.9) at six months, with a matching fall in the mature cross-link histidinohydroxylysinonorleucine — the new collagen remains immature and poorly cross-linked well beyond apparent closure.
  4. Sorensen LT. Wound healing and infection in surgery. The clinical impact of smoking and smoking cessation: a systematic review and meta-analysis. Archives of Surgery. 2012;147(4):373–383.Tier 1Supports: 140 cohort studies, 479,150 patients. Pooled adjusted odds ratios for smokers versus non-smokers: necrosis 3.60 (95% CI 2.62–4.93); healing delay and dehiscence combined 2.07 (1.53–2.81); wound complications 2.27 (1.82–2.84); surgical site infection 1.79 (1.57–2.04). Across four randomised trials, perioperative smoking cessation reduced surgical site infection (OR 0.43, 0.21–0.85) but showed NO significant reduction in other healing complications (OR 0.51, 0.22–1.19 — the interval crosses 1). These are SURGICAL, not aesthetic, outcomes.
  5. Wang AS, Armstrong EJ, Armstrong AW. Corticosteroids and wound healing: clinical considerations in the perioperative period. American Journal of Surgery. 2013;206(3):410–417.Tier 4Supports: Short courses of high-dose systemic corticosteroids lasting under ten days have no clinically important effect on wound healing. In patients taking corticosteroids for at least 30 days before surgery, wound complication rates may be two to five times higher, varying with dose, duration, comorbidity and type of surgery. This is a narrative review of the human literature, not a pooled analysis.
  6. Spring LK, Krakowski AC, Alam M, et al. Isotretinoin and timing of procedural interventions: a systematic review with consensus recommendations. JAMA Dermatology. 2017;153(8):802–809.Tier 1Supports: Systematic PubMed review of English-language articles 1982–2017. Thirty-two relevant publications reported 1,485 procedures — this figure belongs HERE, not to the ASDS consensus paper. States that the belief that isotretinoin within 6 to 12 months of cutaneous surgery contributes to abnormal scarring or delayed healing 'is widely taught and practiced; however, it is based on 3 small case series from the mid-1980s'. Carries the explicit negative: mechanical dermabrasion and fully ablative laser are not recommended during systemic isotretinoin treatment.
  7. Waldman A, Bolotin D, Arndt KA, et al. ASDS Guidelines Task Force: consensus recommendations regarding the safety of lasers, dermabrasion, chemical peels, energy devices, and skin surgery during and after isotretinoin use. Dermatologic Surgery. 2017;43(10):1249–1262.Tier 1Supports: Found insufficient evidence to justify delaying superficial chemical peels or non-ablative lasers — including hair-removal lasers and lights, vascular lasers and non-ablative fractional devices — in patients currently or recently exposed to isotretinoin. Adds, more tentatively, that superficial and focal dermabrasion 'may also be safe when performed by a well-trained clinician'. SCOPE: that cleared list is closed. Skin surgery is not on it, and the paper contains no article or procedure count.
  8. Ou K-L, Wen C-C, Lan C-Y, Chen Y-A, Wang C-H, Wang Y-W. The optimal application of medium potency topical corticosteroids in preventing laser-induced inflammatory responses — an animal study. Life (Basel). 2021;11(4):350.Animal studyTier 4Supports: C57BL/6 MICE, DORSAL SKIN, ablative fractional CO2 laser, groups of six to seven animals. IDENTIFIER CORRECTED 2 Aug 2026 — this record previously carried PMID 33919748, which is a paper about epigallocatechin gallate and heavy-metal oxidative stress. The correct identifier is 33920511. NOTHING HERE ESTABLISHES A HUMAN POST-LASER DOSING RULE. A single application of 0.06% betamethasone valerate immediately after treatment suppressed immediate redness (skin colour at 30 and 120 minutes) with minimal disruption to healing. Dosing for two, three or five days delayed healing dose-dependently: at day nine, crust area and epithelial gap were significantly larger than in untreated controls or the single-dose group, which did not differ from each other. At day 21 the authors also observed more α-SMA-positive myofibroblasts and more collagen in the multi-dose groups — reported as unquantified histology from representative sections, with no cell counts and no p-values, and interpreted by the authors as a HARM of prolonged healing rather than a benefit.

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Skinipedia is written by the educators at MSTA, the medic-led skincare training academy in Liverpool.