How chemical peels work, what each depth can do, and what to expect.

A chemical peel is a controlled, partial-thickness injury to the skin. As the treated layer is replaced, the new skin can show fewer fine lines, more even pigment and smoother texture.^1,2 The depth of injury depends on the acid, its concentration, how long it stays on, how many coats are applied and how wet the applicator is.¹

Peels are used for sun damage and wrinkles, precancerous spots such as actinic keratoses, acne, uneven pigmentation and lines of demarcation after other resurfacing.¹ They cannot tighten loose skin, improve deep scars, shrink pores or remove broken blood vessels.¹

During TCA and phenol peels, the color of the white frost on the skin signals depth. A pink-white frost suggests papillary dermis, dense white suggests upper reticular dermis and gray-white suggests deeper injury.^1,2 Phenol-croton oil is the most aggressive and most effective peel for deep and perioral wrinkles, and it also carries the highest risk of scarring and lightening of the skin.²

Skin type is a key factor. Darker skin types are more prone to dark spots after inflammation, and a personal history of freckles, melasma or dark marks after injury signals that risk in any skin type.^1,2 Fitzpatrick skin types IV - VI are a relative contraindication to medium and deep peels.¹

• Avoid For Now: Active infection or open wounds, including cold sores, and for medium or deep peels, isotretinoin use within the past 6 months.¹
• Use Caution: A history of thick scars or poor healing or prior radiation, and for medium or deep peels, recent deep resurfacing or a recent facelift with extensive undermining.¹
• Skin Conditions: Rosacea, eczema, psoriasis, seborrheic dermatitis and vitiligo can flare or heal slowly after a peel.¹

Skin conditioning with tretinoin and hydroquinone begins at least 6 weeks before a peel, or 8 - 12 weeks in darker skin. It evens out skin thickness so the acid penetrates uniformly, speeds healing and lowers the risk of pigment problems.^1,2 Antiviral medication is given to prevent cold sore outbreaks, and strict sun protection is required before and after.^1,2

• Cleansing: The skin is thoroughly degreased so the acid penetrates evenly.¹
• Application: The acid is applied by facial region, with the head elevated and care taken to keep acid away from the eyes.¹
• Endpoint: Glycolic acid is rinsed off after a set time, while TCA and phenol are judged by the color of the frost.^1,2
• Comfort: Superficial peels sting for 15 - 30 minutes, and medium peels may use a fan, oral medication or nerve blocks.¹
• Monitoring: Phenol peels require heart monitoring and IV fluids, with breaks between facial regions.^1,2

Superficial peels are often repeated every 2 - 4 weeks for the best result, and areas off the face heal 50% - 100% more slowly than the face.¹

Complication risk is directly related to peel depth, and changes in skin pigment are the most common problem.¹

• Darkening: Hyperpigmentation after inflammation is more common in darker skin and with early sun exposure, and it often responds to bleaching creams.^1,2
• Lightening: Hypopigmentation is more common in fair skin and after phenol peels, and it is unlikely to resolve if it persists beyond 3 - 6 months.^1,2
• Prolonged Redness: Redness almost always fades within 6 months, most within 3 months.¹
• Infection: Cold sore reactivation and bacterial or yeast infections are uncommon with antiviral prophylaxis and good wound care.^1,2
• Scarring: The most serious but rare complication, most often around the mouth and jawline, and usually treated with steroid injections.¹
• Milia: Small white cysts that commonly appear about 3 weeks after a peel and respond to topical treatment.¹

Phenol is rapidly absorbed through the skin and can cause heart rhythm problems and kidney or liver toxicity, so deep peels require strict technique and monitoring by highly trained physicians.^1,4 Deep phenol peeling is not performed over facelift skin that has been lifted, although peeling around the mouth and eyes can be combined with a facelift.¹

• Melasma: A systematic review of 24 studies and 1,075 patients found peels safe and effective, with glycolic acid the safest and most effective agent.³
• Darker Skin: In 13 comparative studies of 478 patients with darker skin, peels worked as single treatments for melasma, and TCA and Jessner peels outperformed hydroquinone cream alone.⁵
• Melasma Recurrence: In 40 patients with darker skin treated with sequential glycolic and TCA peels, severity improved without scarring, but melasma returned in 70% within 12 weeks of stopping.⁶
• Acne Scars: In 11 studies of 713 patients, microneedling and chemical peels gave broadly comparable results, and combining them outperformed either alone in a separate meta-analysis.^7,8

• Darker Skin Types: Studies of peels in Fitzpatrick IV - VI skin are small with short follow-up, especially for deeper peels.⁹
• Standard Protocols: Melasma studies vary too much in design to be pooled into a single estimate.³
• Acne Scar Outcomes: Comparisons with other treatments need larger trials with standard outcome measures.⁷