Peels, layer by layer.

Lipid-soluble salicylic acid follows oil into pores, self-limits its own penetration, and holds the best dark-skin record of any peel. The landmark: Grimes treated 25 patients of Fitzpatrick V–VI (acne, post-inflammatory pigment, melasma, oily skin) with five 20–30% peels after hydroquinone priming — safe and effective across all four indications. Multiple controlled comparisons since support it for acne and oily, congested skin.

As a pure anti-wrinkle agent it's secondary — its aging relevance is tone, texture, and keeping breakout-prone skin clear enough for retinoids to do their work.

The classic clinic peel, and the superficial agent with actual controlled data: 50% glycolic applied weekly for four weeks improved rough texture, fine wrinkling, and solar keratoses versus vehicle in a double-blind trial (n=41), with biopsy-confirmed epidermal renewal and, in some specimens, increased dermal collagen.

Perspective for expectations: a comparative RCT found a retinaldehyde cream competitive with a course of glycolic peels — in-office superficial peeling is professional-grade skincare, not a category above good topicals. Concentrations escalate 20→70% across a series; expect mild stinging and a few days of light flaking.

Mandelic acid's large molecule penetrates slowly and evenly — ideal for reactive and deeper-toned skin. In a three-arm trial of 45 Fitzpatrick IV–VI patients, six biweekly 20% salicylic–10% mandelic peels cleared pustules better than 35% glycolic and cut the post-acne pigmentation index from 10.1 to 2.8 (versus 10.9→6.2 for glycolic), with no dropouts for side effects. Small, single-region trials — but consistent, and exactly on-target for the pigment problems that dominate darker-skin aging concerns.

Honest melasma framing first: nothing cures it; photoprotection and topicals are the backbone. Within that, peels earn a place: an RCT in Fitzpatrick IV–VI found glycolic peels plus azelaic acid produced the same ~50% pigment-score reduction as triple-combination cream at 12 weeks, and adding glycolic peels to a Kligman-type cream deepened and sped the response in earlier work. TCA lightens faster but relapses more.

Rules of engagement: prime with hydroquinone, peel gently, expect maintenance forever, and treat any promised "permanent peel cure" as a red flag. (Tranexamic-acid evidence is for creams, tablets, and injections — not peel formulations.)

Resorcinol + salicylic + lactic acid in ethanol. Standalone it performs like a strong superficial peel (it matched 70% glycolic in a 26-patient split-face acne trial, though salicylic acid may beat it on comedones, per a systematic review of 12 acne-peel trials), but its historical importance is as the penetration-equalising first layer under 35% TCA — the combination that defines the modern medium peel (next section). The pairing has support beyond tradition: Jessner's removes part of the epidermis so a lower TCA concentration reaches the same depth (2019 technique review), and in a 24-woman split-face randomised trial in darker-skinned melasma, Jessner's before 20–25% TCA lowered pigment scores more than the same TCA alone. Contains resorcinol, "a strong sensitizer but a rare contact allergen in the clinic", which matters for allergy history, and salicylic acid, which a review of procedures in pregnancy says to avoid or use with caution.

Lactic acid (and gentler cousins like lipohydroxy acid) is positioned as the hydrating, low-irritation AHA for dry or reactive skin. Clinical literature is mostly combination studies and small comparative trials: full-strength lactic acid matched Jessner's solution in a 24-patient split-face melasma study, and a 5–10% lipohydroxy-acid peel matched 20–50% glycolic on fine lines and pigment in a L'Oréal-run split-face trial in 50 women — but there is no controlled photoaging base comparable to glycolic's. A reasonable "first peel ever" or sensitive-skin substitution; not the evidence pick.

The branded heavyweight for stubborn pigmentation: an in-clinic depigmenting mask worn for hours, then a mandatory months-long tapering home regimen. Published support is the maker's own retrospective protocol analysis rather than controlled trials: we found no Cosmelan study at all in PubMed (searched October 2026), and the one indexed Dermamelan study is a 10-woman open-label pilot that reported a 50% improvement in melasma scores. Clinic claims like "95% spot reduction in 99% of patients" are marketing, not literature. It contains genuinely active depigmenting ingredients and helps some melasma patients — but unbranded hydroquinone-based regimens carry far better evidence per euro: the hydroquinone-tretinoin-steroid triple cream beat hydroquinone alone in a Cochrane review of 20 melasma trials. Consider it a committed second-line, not a first stop.

An ingenious pitch — 33% TCA whose epidermal action is blunted by hydrogen peroxide, promising "dermal remodelling with no visible peeling". The retrievable clinical evidence behind the decade-of-studies marketing: a single-centre open-label pilot of five women. Whatever the treatment does, the claims outrun the literature by an unusually wide margin even for aesthetics. If you enjoy it as a glow facial, fine — just don't buy the "remodelling" story at these prices.

The designer-blend tier (TCA + retinoic + salicylic + phenol traces + vitamins) sells convenience and branding. Targeted searching finds no peer-reviewed efficacy trials of the branded products themselves — the evidence is borrowed from their unbranded ingredients at unstated concentrations. They likely perform like the mid-strength peels they contain; you're paying the trademark premium for a mystery ratio. The unbranded classics above have the actual data.

High-dose tretinoin painted on and worn for hours — popular, pleasant, and thinly evidenced: the field's own literature includes a review pointedly titled "Tretinoin peel: a critical view". What is well-supported is daily topical retinoid use (see our collagen guide) and tretinoin as a primer before TCA. The peel format adds theatre to a molecule that works better as a nightly habit.