AHA vs BHA Acids — Which Chemical Exfoliant Is Right for Your Skin?
AHA or BHA — which exfoliating acid should you choose? We compare glycolic, lactic and salicylic acid: how they work, results and uses for every skin type.
What are AHA and BHA acids?
A chemical peel is one of the most effective ways to improve skin texture, fade dark spots and tackle acne. Instead of mechanically scrubbing away the outer layer, exfoliating acids work at the cellular level — they loosen the bonds between dead cells, speeding up their natural shedding. The two biggest groups are alpha-hydroxy acids (AHA) and beta-hydroxy acids (BHA).
Although both types exfoliate the skin, they differ fundamentally in chemical structure and — more importantly — in how they behave on the skin. Understanding these differences is the key to effective skincare.
AHA — water-loving acids for the skin's surface
Alpha-hydroxy acids are water-soluble organic acids. They work on the surface of the epidermis, loosening the bonds between corneocytes (the dead cells of the outer layer) and supporting their natural shedding.
The most important AHAs in skincare:
- Glycolic acid — the smallest molecule, the deepest penetration and the strongest action
- Lactic acid — gentler, with an added hydrating (humectant) effect
- Mandelic acid — large molecules, a very mild action, well suited to skin with rosacea
- Tartaric and malic acid — used as supporting ingredients, rarely as the main active
AHAs are especially recommended for dark spots, rough skin texture, fine lines and dryness. They also help stimulate collagen synthesis.
In Regulation EU 1223/2009, the European Commission sets maximum AHA concentrations for cosmetic products: up to 10% in facial skincare products (pH ≥ 3.5) and up to 6% in rinse-off products. Professional in-clinic formulas may contain far higher concentrations and are used exclusively by specialists.
Looking for products with AHA acids? Browse our exfoliants category and check formulas with our ingredient encyclopedia.
BHA — oil-loving acids that get inside the pores
Beta-hydroxy acids — in cosmetic practice this means above all salicylic acid — differ from AHAs in one crucial way: they are oil-soluble (lipophilic). This means they can penetrate deep into the sebaceous glands and pores clogged with sebum.
This property makes BHAs indispensable for tackling:
- Blackheads and whiteheads (both open and closed comedones)
- Inflammatory acne (comedolytic and anti-inflammatory action)
- Enlarged pores (regular use makes them less visible)
- Oily and combination skin (regulating sebum production)
On top of that, salicylic acid has its own anti-inflammatory action — it inhibits prostaglandin synthesis, which sets it apart from AHAs that act purely as exfoliants. According to data from the SCCS (Scientific Committee on Consumer Safety), salicylic acid is safe in cosmetics at concentrations up to 2% (with the exception of products for children under 3, where it is restricted).
AHA vs BHA — the key differences at a glance
- Solubility: AHA — water-soluble; BHA — oil-soluble
- Depth of action: AHA — the skin's surface; BHA — inside the pores and sebaceous glands
- Main uses: AHA — dark spots, dry skin, ageing; BHA — acne, blackheads, oily skin
- Tolerance for sensitive skin: AHA (lactic, mandelic) — good; BHA (salicylic) — usually good
- Hydrating effect: Lactic acid (AHA) — yes; BHA — none
Which acid should you choose for your skin type?
Dry or normal skin with dark spots: Reach for an AHA — glycolic or lactic acid. Lactic acid is gentler and hydrating at the same time.
Oily or combination skin prone to acne: BHA (salicylic acid) is the obvious choice — it reaches clogged pores and works to calm inflammation.
Skin with acne and post-acne marks: Consider combining both types — BHA in the evening, AHA a few times a week. You can also use combined AHA+BHA products, which are growing in popularity.
Sensitive or reactive skin: Start with the lowest concentrations of lactic or mandelic acid. Avoid glycolic acid if your skin is highly reactive.
The information in this article is for educational purposes. For severe acne, extensive dark spots or skin conditions, consult a dermatologist before adding acids to your routine.
How to use acids safely
- Always apply SPF 30+ in the morning — acids increase the skin's sensitivity to sunlight
- Introduce acids gradually — start with 1–2 times a week
- Don't combine them in a single application with retinoids or other strong acids (risk of irritation)
- After applying an acid toner, wait at least 20–30 minutes before the next layer
- Do a patch test on a small area of skin
FAQ
AHAs (e.g. glycolic and lactic acid) are water-soluble and work on the surface of the skin. BHAs (salicylic acid) are oil-soluble and penetrate deep into the pores. This difference determines what they are used for: AHAs for dark spots and ageing, BHAs for acne and blackheads.
Yes, but not in the same application. The best strategy is to use BHA in the evening and AHA a few times a week (or alternate them). Combined AHA+BHA formulas in a single product are also available and are usually well balanced.
Yes, provided they are used at concentrations regulated by EU law. In Regulation 1223/2009 the European Commission sets the limits (up to 10% AHA in facial products, up to 2% salicylic acid). You should always use SPF protection during the day.
It depends on the concentration and your skin's sensitivity. Everyday products (toners with 5–7% AHA or BHA) can be used once a day or every other day. Stronger peels (10–15% AHA) are used 1–3 times a week. Watch how your skin responds.
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