AHA vs BHA vs PHA: The Complete Guide to Chemical Exfoliants

Short answer: AHAs exfoliate the skin's surface and suit dry or sun-damaged skin. BHAs — led by salicylic acid — work inside the pore and suit oily, acne-prone skin. PHAs are the gentlest of the three and suit sensitive or beginner skin. Most routines benefit from one, not all three at once.

Here's the full breakdown: what each acid actually is, how they work, who they're for, and how to combine them without overloading your skin.

AHA vs BHA vs PHA at a glance

What are AHAs?

Alpha hydroxy acids are a family of water-soluble acids — glycolic acid, lactic acid, malic acid, citric acid, and tartaric acid among them. Most are plant-derived: glycolic acid traditionally from sugarcane, citric acid from citrus, malic acid from apples.

Because they're water-soluble, AHAs work on the surface of the skin rather than penetrating into pores. Molecule size varies between them, which changes how deeply and quickly each one acts — they're not interchangeable, so it's worth knowing which specific AHA a product contains. Glycolic acid has the smallest molecule of the common AHAs, which makes it the most potent — and the one most likely to need a gradual introduction.

What AHAs actually do

Surface exfoliation. AHAs loosen the bonds holding dead skin cells together, helping them shed rather than build up. This is the mechanism behind smoother texture and a brighter-looking complexion.

Hydration. Several AHAs — including glycolic and lactic acid — are also humectants, meaning they draw in and hold water. Similar to how hyaluronic acid works, this adds a hydration benefit on top of the exfoliating one.

Supports collagen-related skin changes. Glycolic acid in particular is one of the more researched AHAs for supporting a firmer-looking complexion over time, alongside its exfoliating role.

Who AHAs suit

• Dry or dehydrated skin
• Dullness and uneven texture
• Early fine lines
• Skin that isn't prone to breakouts or congestion

What are BHAs?

Beta hydroxy acids work differently to AHAs in one critical way: they're oil-soluble. That means a BHA can travel through the oil sitting inside a clogged pore — something a water-soluble AHA can't do as effectively.

The most common BHA by far is salicylic acid, and it's the reason BHAs have a reputation as the go-to acid for acne and congestion.

What BHAs actually do

Penetrates into the pore. This is the defining BHA advantage — it can clear the buildup of oil and dead skin cells inside the pore itself, not just on the surface.

Mild anti-inflammatory effect. Salicylic acid is chemically related to aspirin and carries some of that calming, anti-inflammatory action — part of why it helps with redness alongside congestion.

Supports smaller-looking pores over time. With consistent, appropriate use, ongoing buildup is kept in check, which can make pores appear less prominent.

Who BHAs suit

• Oily or combination skin
• Blackheads and clogged pores
• Acne-prone skin, particularly congestion-driven breakouts
• Skin that also deals with redness or mild inflammation

You'll find salicylic acid across our AHA/BHA range: Exfoliating Cleanser, Exfoliating Tonic, Resurfacing Serum, and the Coco Clay Exfoliating Face Scrub — each formulated to avoid the stinging sensation BHAs are sometimes associated with.

What are PHAs?

Poly hydroxy acids are part of the same broader acid family as AHAs, but with one key structural difference: their molecules are larger. That size difference is what makes them gentler — larger molecules can't penetrate as deeply or as quickly, so they exfoliate with a much lower irritation risk.

Common PHAs include gluconolactone and lactobionic acid.

What PHAs actually do

Gentle surface exfoliation. Because the molecules stay closer to the surface, PHAs exfoliate without the depth of penetration that makes AHAs and BHAs more likely to irritate reactive skin.

Hydration. Like several AHAs, PHAs are humectants — they help draw in and retain moisture alongside their exfoliating role.

Low irritation potential. This is the standout PHA benefit. They're considered suitable for skin types that typically can't tolerate stronger acids at all.

Who PHAs suit

• Sensitive or reactive skin
• Anyone new to chemical exfoliation
• Skin recovering from over-exfoliation or a compromised barrier
• Rosacea-prone or easily inflamed skin

How to choose between them

Dry, dull, or showing early fine lines → start with an AHA like glycolic acid.
Oily, congested, or acne-prone → a BHA, specifically salicylic acid, is the better fit.
Sensitive, reactive, or new to acids entirely → start with a PHA.

If your skin has more than one of these concerns — which is common — a formula that combines acids thoughtfully (rather than stacking multiple single-acid products yourself) is generally the safer route.

Can you use AHAs, BHAs, and PHAs together?

Yes, but not carelessly. Combining acids increases the total exfoliating load on your skin, and too much at once is the most common cause of irritation — not the acids themselves, but the concentration and frequency stacked together.

A few ways to combine them safely:

• AHA + BHA is the most common pairing, and works well for combination skin dealing with both dryness and congestion in different areas.
• PHA + almost anything — PHAs are gentle enough to layer with other acids or actives, and are often used specifically to "clean up" what a stronger AHA or BHA missed.
• PHA + retinol is a workable combination for building tolerance to actives gradually, since PHAs won't compound retinol's own irritation potential the way a stronger acid might.
• Alternate by day or by area if you're not using a combination formula — for example, an AHA on drier areas and a BHA on oilier zones, on different days rather than layering both at once.

How to introduce acids without irritation

• Start with lower frequency — a few times a week, not daily — and build up as your skin tolerates it.
• Introduce one new acid at a time so you can identify what's causing a reaction, if one happens.
• Always follow with a moisturiser. Acids work with a supported barrier, not instead of one.
• Patch test any new product, particularly if you have reactive or sensitive skin.
• Watch for the difference between purging (temporary, resolves within a few weeks) and irritation (gets worse, not better, over time).
• If you're using glycolic acid, daily SPF matters more than usual — it increases sun sensitivity.

Is it safe to use acids every day?

It depends on the acid, the concentration, and your skin's tolerance. PHAs are generally the most forgiving for daily use. AHAs and BHAs are more commonly used a few times a week to start, with frequency increased gradually based on how your skin responds — not a fixed schedule that applies to everyone.

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Frequently Asked Questions About AHAs, BHAs and PHAs

What's the main difference between AHA, BHA, and PHA?
AHAs and PHAs are water-soluble and work on the skin's surface; BHAs are oil-soluble and can penetrate into the pore. PHAs have the largest molecules and are the gentlest of the three.

Which is better for acne, AHA or BHA?
BHA, specifically salicylic acid, is generally the better fit for acne and congestion because it's oil-soluble and can clear buildup inside the pore.

Can I use AHA and BHA in the same routine?
Yes — it's one of the most common combinations, though it's worth introducing gradually and watching for irritation, especially at first.

Are PHAs suitable for sensitive skin?
Yes. PHAs have the lowest irritation potential of the three acid types, largely due to their larger molecule size.

What's the gentlest chemical exfoliant?
PHAs are generally considered the gentlest option, followed by lactic acid among the AHAs.