Salicylic, glycolic or lactic acid?
Most bad experiences with chemical exfoliation come from choosing the wrong acid rather than from exfoliating at all. These three are not interchangeable — they are different molecules that reach different places and solve different problems.
The fundamental split
Exfoliating acids divide into two families, and the difference is solubility.
AHAs — alpha hydroxy acids, including glycolic and lactic — are water-soluble. They work on the surface of the skin, loosening the bonds between dead cells so they shed. Surface texture, tone and dullness are their territory.
BHAs — beta hydroxy acids, in practice salicylic acid — are oil-soluble. That lets them dissolve through sebum and work inside the pore. Congestion, blackheads and oily skin are their territory.
This single distinction resolves most of the choice. If your problem is inside pores, you want a BHA. If it is on the surface, you want an AHA.
Side by side
| Salicylic | Glycolic | Lactic | |
|---|---|---|---|
| Type | BHA, oil-soluble | AHA, water-soluble | AHA, water-soluble |
| Reaches | Inside the pore | Surface, penetrates deepest of the AHAs | Surface, gentlest |
| Best for | Blackheads, congestion, oily skin | Dullness, uneven tone, fine lines | Dryness with dullness, sensitive skin |
| Molecule size | Medium | Smallest — strongest and most irritating | Larger — milder |
| Also does | Anti-inflammatory, calms red spots | Stimulates collagen over time | Hydrates as it exfoliates |
| Typical strength | 0.5–2% | 5–10% at home | 5–10% |
| Avoid if | Aspirin allergy | Skin is reactive or barrier is damaged | Rarely a problem |
Choosing by problem
Blackheads, clogged pores, oily T-zone. Salicylic acid, clearly. Being oil-soluble is the whole point — an AHA cannot get where the problem is. Its anti-inflammatory effect is a bonus if you also get red spots.
Dull, uneven tone, early fine lines. Glycolic acid. Its small molecule penetrates well and it has the strongest evidence for stimulating collagen over sustained use. It is also the most irritating of the three, so start at a low percentage and infrequently.
Dry, sensitive, or new to acids. Lactic acid. The larger molecule works more slowly and superficially, which means less irritation, and it is a humectant — it holds water while it exfoliates, so it does not leave skin as tight. This is the sensible starting point for anyone unsure.
Both congestion and dullness. Use them on different nights rather than mixing. Salicylic on two nights, an AHA on another, never in the same session.
The mistakes that cause most problems
Exfoliating too often. Two to three times a week is right for most people. Daily exfoliation strips the barrier faster than it rebuilds, and the result — tightness, shine, stinging, new breakouts — is often misread as "not exfoliating enough", which makes it worse.
Stacking actives. An acid plus a retinoid on the same night is a common route to irritation. So is an acid plus a strong vitamin C. Alternate nights.
Starting strong. Percentage is not a measure of quality. A well-formulated 5% product at the right pH will outperform a badly formulated 10% one, and will not leave you peeling.
Skipping sunscreen. Exfoliation removes the outer layer of dead cells, which leaves fresher skin more vulnerable to UV. Daily sunscreen is not optional alongside any acid.
How to start
Pick one acid for your main problem. Patch-test on a small area for a few days. Begin once a week, and if there is no irritation after two weeks, go to twice. Mild tingling for a minute is normal; burning, sustained stinging or peeling is not — that means too strong, too often, or both.
Give it eight to twelve weeks before judging. Cell turnover takes roughly a month, so meaningful change needs more than one cycle.
Medical disclaimer. This is general information, not medical or dermatological advice. Patch-test new products, avoid salicylic acid if you are allergic to aspirin, and consult a physician before using acids while pregnant or alongside prescription treatments.