Chemical Exfoliants: AHAs, BHAs, and PHAs Compared

What Chemical Exfoliation Actually Does

Unlike physical scrubs that manually buff the skin's surface, chemical exfoliants use acids to loosen the bonds holding dead skin cells together. When those bonds weaken, surface cells shed more efficiently, revealing newer skin underneath. The result can include smoother texture, more even tone, and — depending on the acid — improved pore appearance or hydration.

Understanding how these acids differ in structure and behavior is key to choosing one suited to your skin. The three main categories — alpha hydroxy acids (AHAs), beta hydroxy acids (BHAs), and polyhydroxy acids (PHAs) — vary in molecular size, solubility, and depth of action. For a broader look at how these fit into a complete routine, see our ingredient reference guide.

AHAs, BHAs, and PHAs: How Each Works

Alpha hydroxy acids (AHAs) — including glycolic, lactic, and mandelic acid — are water-soluble and work primarily on the skin's surface. They dissolve the cellular glue between dead cells at the outermost layer (the stratum corneum). Glycolic acid has the smallest molecule and penetrates most readily; lactic acid is larger and generally considered milder, with some humectant properties that help attract moisture.

Beta hydroxy acids (BHAs) — salicylic acid being the most common — are oil-soluble. This property allows them to pass through the lipid-rich environment of a pore lining, making them uniquely capable of exfoliating inside follicles. That mechanism is why BHAs are frequently associated with reducing blackheads and breakouts in oily skin types.

Polyhydroxy acids (PHAs) — such as gluconolactone and lactobionic acid — have larger molecules that don't penetrate as deeply as AHAs or BHAs. This slower, surface-level action generally translates to less tingling and irritation. PHAs also have demonstrated humectant effects, meaning they help draw water to the skin while exfoliating.

Matching Acid Type to Skin Concern

Skin type and primary concerns should guide your choice more than ingredient trends. Here's a practical framework:

• Dry or dehydrated skin: Lactic acid (an AHA) is a reasonable starting point — it exfoliates while contributing some moisturizing effect. PHAs are another option if sensitivity is also a concern.
• Oily or acne-prone skin: BHAs, particularly salicylic acid, are well-studied for their ability to reduce sebum buildup and unclog pores. Many people with breakout-prone skin tolerate BHAs better than AHAs.
• Uneven tone or surface texture: AHAs like glycolic or mandelic acid can help accelerate surface cell turnover, which may gradually improve the appearance of hyperpigmentation and rough texture.
• Sensitive or rosacea-prone skin: PHAs are generally considered the gentlest entry point, though any acid can provoke a reaction depending on formulation and individual tolerance.

If you're unsure where your skin falls, building a skin-type-matched routine can help clarify your starting point.

Using Chemical Exfoliants Safely

All chemical exfoliants — regardless of category — temporarily increase the skin's sensitivity to UV radiation by removing the outermost protective cell layer. Daily use of broad-spectrum SPF 30 or higher is not optional when incorporating any acid into a routine; it's a basic safety step.

Starting frequency matters: most dermatologists suggest beginning with one to two applications per week and observing how your skin responds before increasing frequency. Concentration also plays a role — lower-concentration formulations are appropriate for daily use by many people, while higher concentrations (typically found in professional treatments) carry greater risk of irritation or barrier disruption.

Avoid combining multiple exfoliant types in the same application unless you have experience and a specific reason to do so. Layering a BHA toner with a glycolic acid serum, for instance, can exceed what the skin barrier handles comfortably. If you're navigating ingredient combinations, decoding ingredient labels can help you spot overlapping actives before they become a problem.

People who are pregnant, nursing, or managing chronic skin conditions should consult a dermatologist before adding any chemical exfoliant to their routine. This article provides general educational information and is not a substitute for professional skincare or medical advice.

This content is intended for general informational purposes only and does not constitute medical or dermatological advice. Consult a qualified healthcare or skincare professional before making changes to your skincare regimen, particularly if you have a skin condition or are in a special health circumstance.