Glycolic, Salicylic, Lactic and TCA: Peel Acids Explained

Each common peel acid works a little differently. Glycolic and lactic acids are alpha hydroxy acids that loosen surface cells and suit dullness, roughness and mild pigment. Salicylic acid is oil-soluble, so it works inside pores and suits oily and acne-prone skin. Trichloroacetic acid (TCA) is a stronger agent that can reach deeper and is used for more significant sun damage and texture. The right choice depends on your concern, your skin type and how much recovery you can manage.

A few terms that help

Peel strength is not just about the name of the acid. Several factors decide how deeply a peel acts:

• Concentration, usually given as a percentage.
• pH, which reflects how much of the acid is free to act. A lower pH generally means a stronger effect.
• Contact time, or how long the acid stays on before it is neutralised or removed.
• Number of layers applied.
• Skin preparation and condition, including recent retinoid use, shaving or irritation.

This is why two "glycolic peels" can behave very differently, and why in-clinic peels are not directly comparable to products sold for home use. Peels are often grouped as superficial, medium or deep; our article on superficial versus medium peels explains those categories.

Glycolic acid

Glycolic acid is an alpha hydroxy acid (AHA) originally derived from sugar cane. It has the smallest molecule of the common AHAs, so it penetrates readily. It works by loosening the bonds between dead surface cells, encouraging them to shed more evenly.

Often considered for: dullness, rough texture, fine surface lines, mild sun damage and some types of uneven pigment.

Things to know: Because it penetrates quickly, glycolic acid can sting more than milder acids and can occasionally penetrate unevenly, especially on irritated skin. In-clinic glycolic peels are usually timed carefully and neutralised. People with sensitive or darker skin may start at lower strengths or choose a gentler acid.

Lactic acid

Lactic acid is another AHA, originally found in milk, with a larger molecule than glycolic acid. It tends to penetrate more slowly, and it also helps the skin hold on to moisture.

Often considered for: dry, sensitive or easily irritated skin, mild dullness and roughness, and as a gentle starting point for people new to peels.

Things to know: Results from lactic acid peels are typically subtle and build over a series. It is a common choice when comfort and low downtime are priorities.

Mandelic acid

Mandelic acid is an AHA derived from bitter almonds. Its molecule is larger still, so it penetrates slowly and evenly. Many people find it less stinging.

Often considered for: sensitive skin, darker skin tones where pigment risk is a concern, mild acne and uneven tone.

Things to know: It is sometimes combined with salicylic acid for acne-prone skin. Like lactic acid, changes tend to be gradual.

Salicylic acid

Salicylic acid is a beta hydroxy acid (BHA). Its key difference is that it dissolves in oil, so it can move into the lining of pores and loosen the mix of oil and dead cells that causes blackheads and breakouts. It also has a mild anti-inflammatory effect.

Often considered for: oily skin, blackheads, whiteheads, mild to moderate acne and some acne-related dark marks. It is frequently used in many skin tones. See chemical peels for acne-prone skin for more.

Things to know: Salicylic acid is related to aspirin, so people with an aspirin allergy should mention it. Applying it to large areas of skin is avoided because of the small risk of absorption into the body. It is generally avoided in pregnancy at peel strengths; discuss options with your physician.

Trichloroacetic acid (TCA)

TCA is not a hydroxy acid. It works by causing proteins in the upper layers of skin to coagulate, which then shed and are replaced. At lower strengths it acts as a superficial peel; at higher strengths it reaches medium depth.

Often considered for: more noticeable sun damage, uneven pigment, fine lines, some shallow scarring and rough texture, usually where a stronger effect is wanted.

Things to know: Medium-depth TCA peels are medical procedures with real downtime: several days of redness, darkening and sheet-like peeling. They carry higher risks of pigment change, infection and scarring, particularly in darker skin, and need careful priming and aftercare. Very high strengths and focal techniques are used only in specific situations.

Combination peels

Many peels blend acids to balance effect and comfort. Jessner's solution, for example, combines salicylic acid, lactic acid and resorcinol, and is sometimes used before TCA. Some peels also include pigment-calming or soothing ingredients. Very deep peels such as phenol peels are a separate category with significant risks and are not part of routine aesthetic care.

Who should not have a peel, or should wait

Regardless of the acid, peels are usually postponed if you have a sunburn, active cold sores or infection, open or irritated skin, flaring eczema or psoriasis, recent oral isotretinoin, recent waxing or resurfacing, or are pregnant or breastfeeding. A keloid history or very reactive skin calls for extra caution. Common side effects include stinging, redness, tightness and flaking; less common risks include dark or light patches, prolonged irritation, cold sore flares and, with stronger peels, scarring.

How the choice is usually made

Choosing an acid starts with your main concern, then your skin type, sensitivity and history of dark marks. Someone with oily skin and blackheads may start with salicylic acid, while someone with dry, sensitive skin and dullness may start with lactic acid. Strength is often increased gradually over a series, depending on how the skin responds. It is also reasonable to decide that daily skincare, rather than a peel, is enough for now.

Frequently asked questions

Which acid is the gentlest?

Lactic and mandelic acids are generally considered gentler starting points, though concentration and pH matter as much as the acid itself.

Is a higher percentage always stronger?

Not necessarily. pH, contact time and layering can make a lower-percentage peel act more strongly than a higher one.

Can I use these acids at home?

Low-strength versions appear in many skincare products. They are milder than clinical peels, but can still irritate if overused or combined with other actives.

If you would like help working out which peel acid, if any, suits your skin, a consultation at HealthPark Medical Aesthetics can walk through your concerns and history and explain the options in plain terms.