How Chemical Peels Resurface Your Skin — From Glycolic to TCA

Medically reviewed by Dr. Dan Xu, M.D., CCFP — CPSO Licensed Physician and Founder & Medical Director of ID Cosmetic Clinic, Markham. Last updated June 2026. This article is general information, not medical advice.

“Chemical peel” sounds dramatic, but the idea is simple and old: use a measured amount of acid to remove a precise depth of skin so that newer, better skin can take its place. The skill is entirely in how deep — and that is decided by which acid, what concentration, how long it stays on, and the experience of the person applying it. This guide explains, in plain language, how peels actually resurface skin, what each major acid does, what results and real downtime to expect, and who should be cautious — written from the perspective of a Markham practice that primarily serves Asian faces, where pigment safety matters more than in any marketing brochure.

How a chemical peel works, step by step

Every peel — from a gentle “lunchtime” glycolic to a medium-depth TCA — follows the same basic mechanism. Only the depth changes.

1. The skin is cleansed and degreased. Oils and residue are removed so the acid penetrates evenly. Uneven prep is one of the most common causes of patchy results.
2. A controlled acid is applied. The solution lowers the pH of the skin’s surface and begins to break down the bonds between cells. Surface acids (AHA/BHA) loosen the “cement” between dead keratinocytes; deeper acids (TCA, phenol) denature protein and cause a controlled injury into the deeper skin.
3. The acid reaches a target depth. The provider watches the skin closely — a light surface peel may cause only mild redness, while a medium peel produces visible “frosting,” a whitish change that tells the physician the acid has reached the right level.
4. The peel is neutralised or self-limits, and shedding begins. Over the next few hours to days, the treated layer flakes or peels away — sometimes barely visible, sometimes obvious sheeting, depending on depth.
5. The skin repairs and rebuilds. As the old layer sheds, skin cells underneath turn over faster. With deeper peels, fibroblasts in the dermis are stimulated to lay down new collagen. The end result is the point of the whole exercise: lighter pigment, refreshed texture, smaller-looking pores and softer fine lines.

In one sentence: a peel removes a defined depth of compromised skin and prompts the skin to replace it with better skin. Everything else is detail about depth and which acid gets you there.

The acids, and what each one does

AHAs — glycolic and lactic acid (surface peels)

Alpha-hydroxy acids (AHAs) are water-soluble acids derived from natural sources such as sugar cane and milk. They work on the skin’s surface, dissolving the bonds between dead surface cells so they shed and reveal brighter skin underneath.

• Glycolic acid has the smallest molecule of the AHAs, so it penetrates most strongly and exfoliates most effectively. Low strengths suit routine maintenance; higher clinical strengths produce a more noticeable surface refresh.
• Lactic acid has a larger molecule and is gentler, with a hydrating quality — a good choice for drier skin or anyone who finds glycolic too aggressive.
• Best for: dull tone, uneven surface pigment, rough texture, enlarged-looking pores, mild congestion and general “glow” maintenance. Surface AHA peels are usually done as a course — for example once a month — for a cumulative effect.

BHA — salicylic acid (the pore peel)

Salicylic acid is a beta-hydroxy acid (BHA), and the key difference is that it is oil-soluble. That lets it travel down into the pore and dissolve the oil and dead-cell plugs that drive breakouts — something water-soluble AHAs cannot do as well. It is also anti-inflammatory and mildly antibacterial, which is why it is a workhorse for acne.

• Best for: acne (blackheads, whiteheads, inflamed bumps), oily skin and clogged pores. It is also a sensible option for people who want exfoliation but find AHAs irritating.
• Note: salicylic acid is chemically related to aspirin, so tell your provider if you have an aspirin allergy. Higher-strength salicylic peels are generally avoided in pregnancy.

TCA — trichloroacetic acid (medium-depth peels)

Trichloroacetic acid (TCA) is the acid where concentration determines depth. At lower strengths it produces a light-to-medium peel; at higher strengths it reaches into the upper dermis. Unlike AHAs and BHAs, TCA works by denaturing protein — it causes a controlled injury and the repair-and-rebuild response that follows, rather than simply unglueing surface cells.

• Best for: more visible pigmentation (including as an adjunct in melasma management), moderate sun damage, fine lines and the appearance of some acne scarring.
• Downtime: a medium-depth TCA peel typically involves around 7–14 days of visible peeling and recovery. This is a real procedure with real downtime — not a lunchtime treatment.

Phenol — deep peels (rarely used today)

Phenol peels are the deepest chemical peels, reaching the deeper dermis. They can produce dramatic results on deep wrinkles and significant sun damage, but recovery runs for weeks, and phenol carries systemic absorption and cardiac risks that demand strict medical monitoring. For these reasons phenol peels are uncommon today, having largely been replaced by safer layered approaches and energy-based devices. We mention it for completeness, not as a routine option.

Peel depth: the single most important decision

Choosing depth is the heart of designing a peel, because depth dictates both how much improvement is possible and how much downtime it costs.

• Superficial (epidermis): little to minimal downtime, light flaking at most. Good for tone maintenance, mild pigment, congestion and pore clarity. Needs a series — typically monthly — for a meaningful cumulative result.
• Medium (papillary dermis): roughly 7–14 days of visible peeling and crusting. A single treatment can improve moderate sun-related pigment, fine lines and superficial scarring — more dramatic than a surface peel, but with more risk and more time off.
• Deep (reticular dermis): recovery measured in weeks, with the most dramatic results but systemic risks that require full medical assessment. Rarely used in modern practice.

A good physician matches depth to your concern and to how much downtime your life can absorb — not to whichever peel sounds most impressive.

Chemical peels at a glance

Figures are typical ranges for general guidance; your plan is set at consultation. This is general information, not medical advice.

What results and downtime to expect

With a superficial peel, most people notice brighter, smoother, more even-looking skin within a few days, with little more than light flaking. The trade-off is that one session does modestly; the visible payoff builds over a course of treatments.

With a medium-depth TCA peel, the first few days bring redness, then visible peeling and flaking for roughly one to two weeks. Once that resolves, the improvement in pigment, texture and fine lines is more pronounced from a single session. You will need to plan around the peeling and protect the new skin diligently from the sun.

Across all depths, two rules hold: rigorous sun protection is non-negotiable both before and after, and you should never pick or pull peeling skin — letting it shed on its own is what protects you from scarring and pigment problems. Individual results vary, and a realistic preview for your skin is something a physician sets in person.

Who chemical peels are for — and who should be cautious

Peels are a versatile, well-established tool, but they are not right for everyone or every moment. You may not be a candidate, or may need a modified plan, if you:

• are pregnant or breastfeeding (higher-strength salicylic and deeper peels are generally avoided);
• have an active skin infection, cold sore outbreak or open wound in the treatment area;
• have recently used isotretinoin (oral acne medication) — a waiting period is usually required;
• have a history of keloid or hypertrophic scarring;
• have very sun-exposed or recently tanned skin;
• are allergic to a peel component (and, for salicylic acid, to aspirin).

A proper consultation screens for all of this before any acid touches your skin. This article is general information, not medical advice — candidacy is decided in person.

Chemical peels and deeper skin tones: the pigment question

For deeper skin tones (Fitzpatrick III–VI), the main risk to manage is post-inflammatory hyperpigmentation (PIH): the inflammation a peel creates can switch on pigment-producing cells, leaving a treated area darker than before rather than clearer. This is precisely the population our Markham practice works with most, and it is why we treat depth conservatively rather than chasing the most aggressive peel.

For deeper skin tones, a careful approach usually means: starting with low-strength superficial peels to see how the skin responds; priming the skin for several weeks beforehand with sun protection and pigment-regulating preparation where appropriate; strict sun avoidance afterwards; and favouring acids with a lower PIH risk profile, such as lactic acid, when suitable. The right peel for darker skin is the one chosen to avoid a pigment flare, not the strongest one available.

The real takeaway

A chemical peel is one of the oldest and most controllable tools in dermatology: choose an acid, choose a depth, remove a defined layer of skin, and let the skin replace it with something better. The intelligence is not in the acid — it is in matching depth to your concern, your skin tone and your downtime, and in respecting pigment risk for skin that is prone to it. Done conservatively and matched to your face, a peel is a quietly powerful resurfacing treatment. Done carelessly, it is the fastest way to cause the very pigment problem you were trying to fix.

Related at ID Cosmetic Clinic

• Treatment: Chemical Peels
• Condition: Melasma & Hyperpigmentation
• Condition: Acne & Acne Scars
• Compare: Chemical Peel vs Laser Resurfacing
• Read next: How to Fade Hyperpigmentation Safely