AHAs and BHAs are both chemical exfoliants, but they work in different places. AHAs (alpha hydroxy acids, such as glycolic and lactic acid) are water-soluble and act on the skin’s surface, so they suit dullness, rough texture and uneven tone, particularly on normal to dry skin. BHA (beta hydroxy acid, which in skincare means salicylic acid) is oil-soluble and works inside pores, so it suits oily, blackhead-prone and breakout-prone skin. Many people only need one of them, a few times a week.
This AHA vs BHA guide explains the difference in plain terms, shows which to choose for your skin, and gives a safe schedule so you get smoother skin without a damaged barrier. It also covers the third group, PHAs, and the mistakes that cause most exfoliation problems.
Key Takeaways
- Exfoliating acids dissolve the bonds between dead skin cells so they shed more evenly, unlike physical scrubs that rub them off.
- AHAs are best for surface texture, dullness, uneven tone and fine lines; BHA is best for clogged pores and oily skin.
- Consumer AHA products are usually formulated at around 5% to 10% (higher strengths are used by professionals); salicylic acid in skincare is commonly 0.5% to 2%.
- Both increase sun sensitivity, so daily sunscreen is not optional.
- Start two nights a week, not daily, and never layer several exfoliants at once.
- Stop and rest your skin if it stings, looks shiny and tight, or flakes constantly.
What AHA and BHA Chemical Exfoliation Does
The outermost layer of your skin is made of dead cells held together by lipids. Normally, those cells shed gradually. With age, sun exposure, dryness or excess oil, the process slows and cells pile up, which can make skin look dull and feel rough or clog pores.
Chemical exfoliants speed up shedding in a controlled way. The advantage over scrubs is evenness: acids work across the whole surface without micro-scratches. The risk is that “more” quickly becomes “too much,” because acids can strip lipids and thin the barrier. That is why the number of times per week matters more than the percentage.
AHAs Explained
Alpha hydroxy acids are water-soluble acids, many originally derived from fruit, milk or sugar cane and now typically made synthetically. They act mostly at the surface and, at suitable strengths, can also increase hydration and gradually improve the look of fine lines and uneven tone.
| AHA | Molecule size | Typical character | Good for |
|---|---|---|---|
| Glycolic acid | Smallest | Most effective, can be most irritating | Dullness, fine lines, texture on tolerant skin |
| Lactic acid | Slightly larger | Gentler, more hydrating | Dry or sensitive skin, beginners |
| Mandelic acid | Larger | Slower penetration, mild | Sensitive skin, tendency to pigment |
| Citric and malic acids | Varies | Often supporting ingredients | Mild surface exfoliation in blends |
Dermatology sources describe AHAs as better suited to normal, dry and ageing skin. Cosmetic safety panels have reviewed AHAs and recommended limits for consumer products, with a common figure of up to 10% at a pH of 3.5 or above, plus sun-protection advice. Higher-strength peels belong in a clinic.
BHA Explained
The BHA used in skincare is salicylic acid. It dissolves in oil, which means it can travel into pores and loosen the mixture of sebum and dead cells that forms blackheads and whiteheads. It also has a mild calming effect on redness, so it often features in acne routines. Typical over-the-counter strengths in leave-on products range from about 0.5% to 2%.
Because it is oil-loving, BHA suits oily and combination skin best. People with very dry or eczema-prone skin often find it too drying. Salicylic acid is related to aspirin, so if you are allergic to aspirin or take certain medicines, ask your doctor or pharmacist before using it widely, especially over large areas. For more on acne choices, see our routine for oily, acne-prone skin.
PHAs: The Gentler Third Option
Polyhydroxy acids, such as gluconolactone and lactobionic acid, are chemically similar to AHAs but have larger molecules, so they penetrate more slowly and tend to irritate less. They also attract water. If you have sensitive or reactive skin and want mild exfoliation, a PHA can be a reasonable starting point, though its effects are subtler and there is less research behind it than for glycolic or salicylic acid.
AHA vs BHA at a Glance
| Feature | AHA | BHA (salicylic acid) |
|---|---|---|
| Solubility | Water | Oil |
| Where it works | Surface of the skin | Surface and inside pores |
| Best skin types | Normal, dry, mature, uneven tone | Oily, combination, blackhead-prone |
| Main goals | Radiance, texture, fine lines, mild pigment | Clogged pores, whiteheads, blackheads, oiliness |
| Typical consumer strength | About 5% to 10% | About 0.5% to 2% |
| Sun sensitivity | Increased; official advice to use sunscreen | Less pronounced; still use sunscreen |
| Common side effects | Stinging, redness, dryness, peeling | Dryness, mild peeling, tightness |
| Frequency to start | 1 to 2 times weekly | 1 to 3 times weekly |
How to Choose Between AHA and BHA
If your main issue is dullness or rough texture
Start with lactic or mandelic acid for a few weeks. Move to glycolic only if your skin tolerates it.
If you have blackheads, large-looking pores or oily T-zone
A BHA is the natural choice. Our guide to minimising the look of large pores explains why pore size itself cannot change, but clearing congestion can make pores look smaller.
If you have both texture and oiliness
Use BHA on the oily areas on some nights and a gentle AHA on others, never together at first. Another option is to choose a single product that combines both at low strengths.
If you have sensitive skin, rosacea or eczema
Try a PHA or very low-strength lactic acid cautiously, or skip chemical exfoliation and focus on moisturiser. See a dermatologist if your skin is inflamed. Flaking often needs hydration, not more exfoliation.
If you have darker skin or tend to get dark marks
Exfoliation can help fade surface pigment, but over-exfoliating causes irritation that leaves marks. Choose gentle acids such as mandelic or lactic, go slowly and use sunscreen. Gentle and consistent works best for pigment-prone skin.
A Starter Schedule That Protects Your Barrier
This is an illustrative four-week plan for a beginner using one acid. Adjust to your skin and any label instructions.
| Week | Exfoliant nights | Other nights |
|---|---|---|
| 1 | One night (for example Wednesday) | Cleanser and moisturiser only |
| 2 | Two nights (Mon, Thu) | Cleanser and moisturiser only |
| 3 | Two nights, same pattern | Cleanser and moisturiser only |
| 4 | Two to three nights if no irritation | Optional gentle hydrating serum |
Apply the acid to clean, dry skin, wait a few minutes, then moisturise. Use it at night for convenience, and wear sunscreen every morning. The order of products is covered in our morning and night routine guide.
What to Avoid Pairing With Acids
- Retinoids: These also speed turnover. Using both on the same night is a common cause of burning. Alternate nights.
- Physical scrubs and cleansing brushes: Double exfoliation is rarely helpful.
- Several acids layered together: One exfoliant per session is enough.
- Benzoyl peroxide or prescription acne treatments: Ask your clinician before combining.
- Hair removal, waxing and sunbeds on the same day.
Signs You Are Overdoing It
Watch for a shiny, tight look, stinging with products that used to feel fine, new redness, flaking that makeup will not hide, and sudden breakouts. These suggest barrier damage. If you notice them, stop all exfoliants and active products for one to two weeks, use a bland cleanser, a rich fragrance-free moisturiser and sunscreen, and read our guide to repairing the skin barrier. See a doctor if you see blistering, swelling, severe pain or signs of infection.
Sun Safety Is Part of the Deal
Exfoliating acids remove the outer layer that gives some natural protection, which is why regulators, including the US Food and Drug Administration, have advised that AHAs can increase sensitivity to sunlight and recommend sunscreen and other protection while using them and for about a week afterward. If you cannot commit to daily sunscreen, do not start an acid.
Body and Scalp Use
Acids are not only for faces. Lactic acid body lotions are popular for rough upper arms, and salicylic acid washes are used on the chest and back where breakouts are common. The same rules apply: go slowly, moisturise and avoid broken skin. Do not use on irritated or freshly shaved skin.
Reading Labels Without Getting Fooled
Marketing names can hide what is actually in the bottle. Look at the ingredient list for glycolic, lactic, mandelic, malic, citric or tartaric acid (AHAs), salicylic acid or willow bark extract (BHA-related), and gluconolactone or lactobionic acid (PHAs). Willow bark extract is not the same as pure salicylic acid, and its exfoliating effect is usually weaker, so do not assume equal results.
Percentages matter only alongside pH. An acid exfoliates properly when the product is acidic enough for the acid to stay in its active form, commonly a pH somewhere between about 3 and 4. A lower pH acts more strongly and irritates more, while a product with a higher pH may do very little even at a high percentage. Many brands do not publish pH, so judge by how your skin responds and by the guidance on the label. Words such as “peel,” “resurfacing” or “10-minute mask” signal a stronger, short-contact product, which belongs in a once-a-week slot, not an everyday one.
Practical buying checks
- Choose opaque or airless packaging, which helps keep formulas stable.
- Patch test behind the ear or on the inner forearm for two to three days.
- Be wary of products that promise visible change in a single use.
- Check the expiry symbol (the open-jar icon) and discard after the stated months.
Frequently Asked Questions
Can I use AHA and BHA together?
Some products combine low strengths of both, and some people tolerate alternate-night use. Do not layer separate full-strength products in one routine, especially at the start.
Which is better for acne, AHA or BHA?
BHA is generally the better fit for clogged pores and oily acne-prone skin, because it works inside the pore. AHAs may help with the marks acne leaves behind.
How often should I exfoliate?
Most people do well with one to three times a week. Daily use is possible with very mild leave-on products, but it is rarely necessary.
Is glycolic acid too strong for sensitive skin?
It can be. Lactic, mandelic or PHAs are gentler starting points.
Do I need to rinse off AHA or BHA?
Leave-on serums and toners are not rinsed. Cleansers and masks are rinsed after the stated time. Follow the label.
Can I use them in pregnancy?
Low-strength topical products are often considered acceptable, but high-strength salicylic acid peels are typically avoided. Check with your doctor or midwife.
Why is my skin purging?
Mild extra breakouts can happen in the first few weeks because of faster cell turnover, but burning, swelling or a spreading rash is irritation, not purging. Stop and seek advice.
Should I exfoliate in the morning or at night?
Night is easier because you avoid sun straight afterward, but low-strength morning use is fine with sunscreen.
The Bottom Line
The simplest AHA vs BHA rule is this: choose an AHA for surface dullness and texture, a BHA for clogged, oily pores, and a PHA if your skin is sensitive. Start with one product, use it once or twice a week, moisturise, and wear sunscreen every day. More acid does not mean better skin. If your skin is inflamed, scarred or reacting badly, a dermatologist can tailor treatment safely.
This article is for general informational purposes only and does not replace advice from a qualified healthcare professional. Individual needs differ, and costs, rules and guidelines change — please check with a doctor, pharmacist, or the relevant official source for guidance specific to your situation.
