What Exfoliating Acids Actually Do

Exfoliating acids work by loosening the bonds that hold dead skin cells together on the surface of your skin — a process called chemical exfoliation. Unlike physical scrubs, they don't rely on abrasion. Instead, they break down the "glue" between cells so that built-up layers shed more efficiently, revealing fresher skin underneath.

There are three main families: alpha hydroxy acids (AHAs), beta hydroxy acids (BHAs), and polyhydroxy acids (PHAs). Each has a distinct molecular structure, skin affinity, and use case. Knowing the difference helps you understand why a product may or may not be suited to your skin's needs — and how to use it without unnecessary irritation.

If you're building a routine from scratch, this beginner's roadmap is a great place to start before introducing any actives.

Chemical exfoliation

The process of using acids or enzymes to dissolve the bonds between dead skin cells, encouraging them to shed without physical scrubbing.

Alpha hydroxy acid (AHA)

A class of water-soluble exfoliating acids derived from natural sources such as fruit or milk, primarily effective on the skin's surface. Examples include glycolic and lactic acid.

Beta hydroxy acid (BHA)

An oil-soluble exfoliating acid — most commonly salicylic acid — that can penetrate into pores to dissolve sebum and debris.

Polyhydroxy acid (PHA)

A class of larger-molecule exfoliating acids that work gently on the skin's outer layers, often better tolerated by sensitive skin types.

Skin barrier

The outermost layer of the skin that regulates moisture loss and protects against environmental irritants. Over-exfoliation can compromise it.

Humectant

An ingredient that draws moisture from the environment or deeper skin layers to the skin's surface, helping maintain hydration.

AHAs, BHAs, and PHAs: A Side-by-Side Reference

Each acid family targets different concerns and behaves differently in skin tissue. Here's what the research-supported science tells us about each:

AHA solubility Water-soluble
BHA solubility Oil-soluble
Gentlest acid family PHAs (largest molecule, slowest penetration)
Best known AHAs Glycolic acid, lactic acid, mandelic acid
Best known BHA Salicylic acid
Best known PHAs Gluconolactone, lactobionic acid
Primary AHA targets Uneven texture, dullness, surface hyperpigmentation
Primary BHA targets Clogged pores, blackheads, oily or acne-prone skin

Alpha Hydroxy Acids (AHAs)

AHAs — including glycolic acid, lactic acid, and mandelic acid — are water-soluble and work primarily on the skin's surface. Glycolic acid has the smallest molecule of the group, allowing it to penetrate readily; lactic acid is gentler and also has humectant (moisture-attracting) properties. AHAs are commonly used to address uneven texture, dullness, and mild hyperpigmentation. They can also support collagen synthesis over time, according to general dermatology literature. Because they increase photosensitivity, daily sunscreen use is essential.

Beta Hydroxy Acids (BHAs)

The most widely discussed BHA is salicylic acid, which is oil-soluble. This property allows it to penetrate into pores and dissolve the sebum and debris that contribute to blackheads and breakouts. BHAs are generally considered well-suited for oily, acne-prone, or congested skin types. Salicylic acid also has mild anti-inflammatory properties, which may make it more tolerable for some people compared to AHAs. Those with aspirin sensitivities should consult a healthcare provider before use, as salicylic acid is chemically related.

Polyhydroxy Acids (PHAs)

PHAs — such as gluconolactone and lactobionic acid — are larger molecules that exfoliate more slowly and stay closer to the skin's outer layers. This makes them among the gentler options in the acid family, often better tolerated by sensitive or reactive skin. PHAs also have antioxidant and humectant properties. Some research suggests they may be compatible with conditions like rosacea where other acids are typically too aggressive, though individual responses vary and a dermatologist's guidance is advisable in those cases.

Understanding how these acids fit into your full routine matters — see how to layer actives without canceling their benefits for practical guidance on sequencing.

Using Acids Safely: What to Keep in Mind

Exfoliating acids are among the more potent actives in everyday skincare, and a few principles consistently appear across dermatology education:

  • Start low and slow. Lower concentrations used infrequently (once or twice a week) allow your skin to adjust before increasing frequency.
  • Don't layer multiple acids at once unless a product is specifically formulated to combine them safely. Stacking acids increases the risk of irritation and barrier disruption.
  • Always use SPF. AHAs in particular increase UV sensitivity. Broad-spectrum sunscreen daily is non-negotiable when using these ingredients.
  • Watch for signs of over-exfoliation — persistent redness, stinging, tightness, or peeling beyond normal turnover. If these appear, reduce frequency or stop use and allow your skin barrier to recover.
  • Certain ingredients don't play well together. Retinoids, for instance, used at the same time as acids can increase irritation risk. Learn more about ingredient pairing before combining actives.

Acids and Skincare Sequence Matter

Acids are typically applied after cleansing and toning, before heavier serums and moisturizers. Where exactly they land in your lineup can affect how well they work. For a detailed breakdown of product ordering, see skincare layering before makeup. Getting the sequence right helps every product do its job.

This article is for general informational and educational purposes only and is not a substitute for advice from a licensed dermatologist or healthcare professional. If you have a skin condition or concerns about how acids may interact with medications or treatments, consult a qualified provider.