Skincare

How often to exfoliate: by skin type and acid

No dermatology body publishes a weekly number, so read 1 to 2 sessions a week as a starting convention rather than a dose, and expect the more aggressive product to belong on your skin less often. Strength is set by pH as much as by percentage: an EU committee suggested in 2000, as advice and not law, that leave-on glycolic acid stay at or below 4 percent at pH 3.8 or above and lactic acid at or below 2.5 percent at pH 5 or above, while EU law does cap salicylic acid at 2.0 percent in most products. Frequency matters because acids change how skin answers sunlight: in 16 volunteers, 4 weeks of a 10 percent glycolic acid at pH 3.5 measurably lowered the dose of UV needed to redden skin, and that faded 1 week after use stopped.

What exfoliating actually does

Alpha hydroxy acids loosen the bonds between dead cells, which speeds turnover in the outermost layer. Glycolic acid is alpha hydroxy acetic acid and lactic acid is alpha hydroxy propionic acid, the 2 used most in cosmetics. They work only in the un-ionised form, so the effect rises as the formula becomes more acidic: turnover peaks around pH 3, with a useful band of about pH 2.8 to 4.8. Salicylic acid is lipid soluble instead, mixing with the oils of the epidermis and the sebaceous follicle, which is why it is the acid usually picked for blocked pores rather than for flat, flaky texture.

What sits on a shelf varies more than the labels suggest. The market figures the EU committee prints are from a US Food and Drug Administration analysis, not an EU survey: glycolic acid in 67 percent of consumer products at 1 to 26 percent and pH 2.42 to 4.26, lactic acid in 22 percent at 0.4 to 9 percent, salon preparations at 3 to 67 percent glycolic acid. Mechanical exfoliation takes cells off by friction, and the American Academy of Dermatology sets the method out plainly: small circular motions for about 30 seconds, a rinse with lukewarm rather than hot water, moisturiser after, and never over open cuts or sunburnt skin.

Why pH matters more than the percentage

The most useful finding in the EU review is that pH, not concentration, drives irritation. In cumulative irritation testing, 13 percent glycolic acid at pH 4.4 came out less irritating than 8 percent glycolic acid at pH 3.25. Formulation can override both: one 8 percent glycolic acid at pH 3.6 was rated milder than some 4 percent products at pH 3.7, which ran from slightly to severely irritating. A percentage on a label with no pH beside it tells you very little.

The EU position on leave-on products is precautionary, specific and 26 years old. On the evidence available in 2000, the committee suggested glycolic acid at up to 4 percent at a pH of 3.8 or above, and lactic acid at up to 2.5 percent at a pH of 5 or above, with warnings to keep it from the eyes and to protect the skin from UV during use. That is advice, not law: neither acid appears in the annexes of the EU Cosmetics Regulation, so a 10 percent glycolic acid serum is legal. An industry panel in 1997 had set a looser bar, 10 percent at pH 3.5 for consumer products and 30 percent at pH 3.0 for salon use with rinsing and a trained operator.

Salicylic acid is the one with law behind it. Under the EU Cosmetics Regulation, amended in 2021, it is capped at 2.0 percent in most products, 3.0 percent in rinse-off hair products and 0.5 percent in body lotion and in eye products such as mascara and eyeliner, with a separate 0.5 percent ceiling as a preservative and a ban for children under 3. So a 10 percent salicylic acid lotion is not a legal face product in the EU. Our comparison of glycolic, lactic and salicylic acid takes the differences ingredient by ingredient.

A starting frequency by skin type

No dermatology body publishes a weekly number: frequency depends on the method, the strength and the skin in front of you. The American Academy of Dermatology says as much, then gives the working principle, that the more aggressive the exfoliation, the less often it needs doing. Dry, sensitive or acne-prone skin may do better with a washcloth and a mild chemical exfoliator, while oily or thicker skin usually copes with stronger chemical or mechanical options. The table below is a conservative starting point rather than a prescription.

Treat the first month as a test: 1 acid, 1 night a week for 2 weeks, then a second night only if the skin stays calm. Irritation is common even at strengths that sound trivial: when 100 people applied a 0.5 percent mixture of lactic and glycolic acid to the face once a day for 6 weeks, 26 percent reported itching or stinging. Tightness, a shine that is really inflammation, or new flaking are signs to stop for 2 weeks instead of exfoliating harder. The Barrier Check runs through those signs, and the Skin Type Finder settles which row you belong in.

Sun sensitivity sets the ceiling

Frequency is not only a question of stinging. In a study run for the US Food and Drug Administration, 16 volunteers with skin types 1 to 3 applied 2 mg per square centimetre of a 10 percent glycolic acid at pH 3.5 to the back daily for 4 weeks. The minimal erythema dose, the UV that just reddens skin, fell to 11.8 on treated sites against 14.4 on the vehicle control, reported at p below 0.01, with sunburn cells rising too. One week after the applications stopped, the gap had closed, 13.4 against 14.3.

Lower strengths behave more gently. Twice daily 4 percent glycolic acid at pH 3.8 on the lower back for 3 months produced a 13 percent fall in that same dose, though 3 volunteers fell by 48 to 50 percent, while a 1.4 percent blend at pH 4.2 twice a day for 6 months showed no significant effect. These were small studies, mostly 12 to 16 people, on backs and forearms rather than faces and in pale skin types, so they describe short term photosensitivity and say nothing about long term risk. Sun protection is part of the routine while you use an acid: the British Association of Dermatologists asks people with rosacea for SPF 30 or higher on the face every day, a fair floor for anyone exfoliating.

Skin that needs less, or none at all

With rosacea the first instruction from the British Association of Dermatologists is not to rub or scrub the face while cleansing, because that makes rosacea worse. A soap substitute, an unperfumed moisturiser and daily SPF 30 or higher do more than any acid. With eczema the barrier is already broken, so acids sting, spread the irritation and slow healing, and the emollient is the step that earns its place. If skin is weeping, cracked or sunburnt, exfoliation waits, and a rash that spreads belongs with a pharmacist or doctor.

Retinoid users need the most care with the calendar. Prescription retinoid creams, retinol and benzoyl peroxide already make skin more sensitive and more likely to peel, and the American Academy of Dermatology warns that exfoliating on top of them can worsen dryness or set off breakouts. Keep them to separate nights, hold the acid at 1 night a week while you build a retinoid up, and drop it while the skin is flaking. Our guide to retinol, retinal and tretinoin sets out the ramp, and purging against a breakout covers those first weeks.

If you have a darker skin tone, or already see dark spots, the Academy advises against strong chemical or mechanical exfoliation, because the irritation itself can leave pigment behind. The controlled version is a professional peel: 20 to 30 percent salicylic acid, commonly 3 to 6 sessions 2 to 4 weeks apart, from a clinician who has seen your skin and knows what else you take. Side effects are recorded even there: in 1 study of 25 people with skin of colour, 16 percent had mild ones, and among 35 Korean patients redness beyond 2 days reached 8.8 percent and dryness 32.3 percent. That review gives salicylic acid the old US pregnancy category C label and advises against peels in pregnancy, so ask a doctor first if you are pregnant or breastfeeding, keep any acid to a small area, and skip salicylic acid if aspirin does not agree with you.

A 4 week test run

Frequently asked

How often should I exfoliate?

No dermatology body sets a weekly number, so 1 to 2 sessions a week is a convention rather than a tested dose. Published advice ties frequency to the method, since the more aggressive the product the less often it should be used, so start at 1 night a week for 2 to 4 weeks before you add a second.

Is lactic acid gentler than glycolic acid?

It is held to lower strengths in leave-on products, up to 2.5 percent at pH 5 or above against 4 percent at pH 3.8 for glycolic acid in the EU advisory position. pH does more than the percentage: 13 percent glycolic acid at pH 4.4 tested milder than 8 percent at pH 3.25.

Can I exfoliate while using a retinoid?

Not on the same night. Retinoid creams, retinol and benzoyl peroxide already leave skin more sensitive and more likely to peel, so an acid on top tends to worsen dryness or set off spots. Hold the acid at 1 night a week, or pause it while you build the retinoid up.

Do acids make skin more sensitive to the sun?

Yes, while you are using them. In 16 volunteers, 4 weeks of a 10 percent glycolic acid at pH 3.5 left the dose of UV needed to redden skin at 11.8 on treated sites against 14.4 on the vehicle control, and the effect had gone 1 week after stopping. Use SPF 30 or higher daily throughout.

I have rosacea. Can I use an exfoliating acid?

Take advice first. The British Association of Dermatologists tells people with rosacea not to rub or scrub the face, to cleanse with a soap substitute and to apply SPF 30 or higher every day, and its leaflet names no exfoliating step. Rosacea-prone skin often reacts to acids, so ask a doctor or pharmacist before trying one.

Is a scrub worse than an acid?

Not automatically, but it is easier to overdo. If you use one, keep it to about 30 seconds of small circular motions, rinse with lukewarm water and moisturise, and avoid strong mechanical exfoliation altogether if you have a darker skin tone or dark spots.

Sources

• American Academy of Dermatology, how to safely exfoliate at home · Source of the principle that frequency depends on skin type and method and that the more aggressive the method the less often it should be done, the advice for dry, sensitive and acne-prone skin, the warning about retinoid creams, retinol and benzoyl peroxide, the caution for darker skin tones and dark spots, and the 30 seconds of small circular motions with lukewarm water and moisturiser after.
• Scientific Committee on Cosmetic Products and Non-Food Products, position paper on the safety of alpha hydroxy acids, SCCNFP/0370/00 · Adopted 28 June 2000, a non-binding scientific position and not law. Source of the suggested leave-on levels of 4 percent glycolic acid at pH 3.8 or above and 2.5 percent lactic acid at pH 5 or above, the market figures it reprints from a US Food and Drug Administration analysis, the 1997 industry panel limits of 10 percent at pH 3.5 and 30 percent at pH 3.0, the finding that pH matters more than concentration, the irritation figures, and the sun sensitivity studies with 16 volunteers and the minimal erythema dose values of 11.8, 14.4, 13.4 and 14.3.
• Regulation (EC) No 1223/2009 on cosmetic products, consolidated text of 1 May 2025, Annexes III and V · Entry 98 of Annex III, in the wording given to it by Commission Regulation (EU) 2021/850, sets salicylic acid at 3.0 percent for rinse-off hair products, 2.0 percent for other products and 0.5 percent for body lotion, eye shadow, mascara, eyeliner, lipstick and roll-on deodorant, with a ban for children under 3 years of age. Annex V entry 3 allows 0.5 percent as a preservative. Glycolic acid and lactic acid have no entry in these annexes.
• Salicylic acid as a peeling agent, a comprehensive review, Clinical, Cosmetic and Investigational Dermatology · Source of the peel figures: 20 to 30 percent superficial peels, 3 to 6 sessions at intervals of 2 to 4 weeks, the lipid solubility that takes salicylic acid into the sebaceous follicle, 16 percent mild side effects among 25 people with skin of colour (20 African American and 5 Hispanic participants), 8.8 percent prolonged redness and 32.3 percent dryness among 35 Korean patients, and the pregnancy category C classification under the former US labelling system, with peels not recommended in pregnancy.
• British Association of Dermatologists, patient information leaflet on rosacea · Source of the rosacea advice used here: do not rub or scrub the face when cleansing, cleanse with a soap substitute, use an unperfumed moisturiser, and apply a sun block of SPF 30 or higher to the face every day.

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This guide is for general information. It does not replace advice from a dermatologist, physician or qualified practitioner, or an examination.