Exfoliating Acids Explained: A Field Guide

“Exfoliating acid” is a big tent. Under it sit a handful of ingredient families that behave quite differently — some work on the surface, one dives into your pores, others barely penetrate at all — and the marketing rarely explains which is which. This page is the field guide: every common acid in one table, what each one actually does, how gentle it is, and the concentrations where “stronger” stops meaning “better.”

The one idea that ties them together: molecule size

Most of what separates these acids comes down to two things: whether they dissolve in water or oil, and how big the molecule is. Water-solubleacids (the AHAs) work mainly on the skin’s surface. The oil-soluble one (salicylic acid, a BHA) can get down into oily pores. And across the board, a smaller molecule penetrates faster and more deeply— which usually means more potency but also more potential for irritation — while a larger molecule works more slowly and gently. Keep that in mind and the whole table below starts to make sense.

Every exfoliating acid at a glance

The AHAs: surface, tone and texture

Alpha hydroxy acids are your go-to for surface smoothing and even tone— dullness, rough texture, sun-related discoloration and early fine lines. They share a family resemblance but differ mainly in strength, which tracks their molecule size.

Glycolic acid

The smallest AHA and the deepest-penetrating, which makes it the most potent — and the most likely to tingle. It’s the classic “glow” acid for texture and brightness, and a great pick once you know your skin tolerates acids. Start low. We compare it directly to salicylic on glycolic acid vs. salicylic acid.

Lactic acid

A step gentler than glycolic thanks to its larger molecule, with a reputation for being more hydrating. It’s an easy all-rounder and a sensible entry point for anyone who finds glycolic too much.

Mandelic acid

The largest common AHA, so it works slowly and evenly with the least irritation. That makes it a favorite for sensitive skin and for evening out tone gently over time — the tortoise that quietly wins.

The BHA: into the pores

There’s really one BHA you’ll meet: salicylic acid. Its defining trait is that it’s oil-soluble, so unlike the water-loving AHAs it can travel into an oily pore and dissolve the mix of sebum and dead skin that causes blackheads and breakouts. If your concern is congestion, oiliness or acne rather than surface tone, this is usually the acid you want. The AHA vs. BHA comparison lays out the full split.

PHAs: the gentle option

Polyhydroxy acids — names like gluconolactone and lactobionic acid— are essentially larger, gentler relatives of the AHAs. Their bigger molecules stay closer to the surface, so they exfoliate more mildly, and they carry water-binding, humectant qualities on top. If AHAs have always felt like too much, or your skin is easily irritated, PHAs are the low-drama way to get some exfoliation.

Azelaic acid: the multitasker

Azelaic acid isn’t a classic exfoliating acid at all — it’s a dicarboxylic acid that works differently — but it lives in this conversation because it’s so useful and so well tolerated. It targets redness, bumps, breakouts and uneven tone at once, and it tends to sit comfortably even on sensitive, redness-prone skin. Think of it less as a peel and more as a gentle all-purpose corrector. Our azelaic acid picks cover the formats worth trying.

How strong is too strong?

This is where people go wrong most often: they reach for the highest percentage on the shelf, assuming more equals better. It doesn’t. Higher concentrations mainly buy you more irritation, and past a point that works against you by damaging the barrier you need intact.

• Daily leave-on AHAs: single digits up to around 10 percent is plenty for most people. Regulatory guidance on alpha hydroxy acids centers on lower-strength everyday products; very high strengths belong to occasional or professional peels, not nightly use.
• Salicylic acid:over-the-counter products top out at about 2 percent. You don’t need more than that for everyday pore care.
• Azelaic acid: around 10 percent is the common non-prescription strength; higher percentages generally come from a prescriber.

A good rule: start at the lower end, use one acid rather than several, and let frequency — not concentration — be the dial you turn up. And because every acid here can increase your sensitivity to the sun, daily broad-spectrum sunscreen isn’t optional while you use them.

The short version

AHAs (glycolic, lactic, mandelic) smooth the surface and even tone, and get gentler as the molecule gets bigger. Salicylic, the oil-soluble BHA, clears pores. PHAs are the gentlest exfoliation for sensitive skin. Azelaic is the calm multitasker for redness and tone. Match the acid to your concern, keep the strength modest, use just one at a time, and wear sunscreen — that’s the entire field guide. When you’re ready for specific products, start with our best chemical exfoliants.