AHA (glycolic, lactic acid) works on the skin's surface and suits dry or sun-conscious skin; BHA (salicylic acid) is oil-soluble and better for oily, congested, or acne-prone skin; PHA is the gentlest option, suited to sensitive or reactive skin that reacts to stronger acids. All three exfoliate, but the right pick depends on your skin type and tolerance.
What Chemical Exfoliants Actually Do
Chemical exfoliants work by loosening the bonds between dead skin cells on the skin's surface, encouraging them to shed more evenly than they would on their own. This is different from physical exfoliation (scrubs, brushes), which manually buffs skin. Chemical exfoliants are generally considered gentler on the skin barrier when used correctly, though "gentler" doesn't mean risk-free — overuse of any acid can lead to irritation, dryness, or increased sun sensitivity.
The three main categories — AHA, BHA, and PHA — are grouped by their chemical structure and solubility, which affects where and how they work on the skin.
Why the Distinction Matters
It's tempting to treat "chemical exfoliant" as one interchangeable category, but the differences matter in practice. Someone with oily, breakout-prone skin who reaches for a pure AHA product may find it doesn't address the congestion they're trying to manage. Someone with sensitive, easily-flushed skin who jumps into a high-percentage BHA or AHA product may end up with redness and a compromised barrier. Matching the exfoliant type to your skin's actual needs — rather than picking whatever is trending — tends to produce a more comfortable, sustainable routine.
AHA: Alpha Hydroxy Acids
AHAs are water-soluble acids derived from fruit, milk, or sugar cane sources (though most in skincare are lab-synthesized for consistency). The most common ones you'll see on ingredient lists are glycolic acid, lactic acid, mandelic acid, and tartaric acid.
How AHAs Work
Because AHAs are water-soluble, they work primarily on the surface of the skin, helping to loosen the connections between dead skin cells. This can leave skin looking brighter and feeling smoother. Glycolic acid has the smallest molecular size among common AHAs, which allows it to penetrate more readily — this is part of why it's considered one of the more potent options, and also why it can be more likely to cause sensitivity in some people compared to lactic or mandelic acid.
Who AHAs Tend to Suit
- Normal to dry skin types, since AHAs are humectant-adjacent and often paired with hydrating ingredients
- People primarily concerned with surface texture, dullness, or uneven tone
- Those without significant active acne or oil congestion
Lactic acid is often recommended as a starting point for people newer to chemical exfoliation, since it tends to be milder than glycolic acid while still working on similar mechanisms. Mandelic acid, with its larger molecule size, is sometimes positioned as a good option for those wanting AHA benefits with a gentler feel.
AHA Caveats
AHAs can increase photosensitivity, so daily sunscreen use becomes even more important when they're part of a routine. They can also cause a stinging or tingling sensation on first use, which usually settles as skin adjusts — though persistent burning or redness is a sign to scale back frequency or concentration.
BHA: Beta Hydroxy Acids
The main BHA used in skincare is salicylic acid, along with its derivative betaine salicylate. Unlike AHAs, BHA is oil-soluble.
How BHA Works
Because salicylic acid can dissolve in oil, it's able to get into pores and work within the oil-filled follicle, rather than staying strictly on the skin's surface. This is why BHA is so frequently recommended for oily and acne-prone skin — it can help address the inside of the pore, not just the top layer of skin. Salicylic acid is also often noted for having some anti-inflammatory properties, which is part of why it's a common ingredient in formulations aimed at blemish-prone skin.
Who BHA Tends to Suit
- Oily or combination skin with visible congestion or blackheads
- Those dealing with occasional breakouts or enlarged-looking pores
- Skin that tends to feel greasy rather than tight or flaky
BHA Caveats
Because it can be drying, especially at higher concentrations or with frequent use, BHA isn't automatically the right choice just because someone has acne — dry, acne-prone skin might actually respond better to a milder acid or lower frequency. Salicylic acid is derived from the same family as aspirin, so those with a known salicylate sensitivity or allergy should check with a healthcare provider before using it.
PHA: Polyhydroxy Acids
PHAs are a newer, less widely known category that includes ingredients like gluconolactone and lactobionic acid. Structurally, PHA molecules are larger than both AHA and BHA molecules.
How PHA Works
Because the PHA molecule is larger, it penetrates the skin more slowly and superficially than AHA or BHA. This generally makes it feel milder on application, with less of the tingling or stinging some people experience with AHAs. PHAs are also considered to have humectant properties, meaning they can help draw in moisture at the same time they exfoliate.
Who PHA Tends to Suit
- Sensitive, reactive, or easily irritated skin
- Rosacea-prone or eczema-prone skin (though it's worth checking with a dermatologist given individual variability)
- People new to chemical exfoliation who want to start conservatively
- Those who found AHA or BHA products too harsh in the past
PHA Caveats
Because PHAs work more gently and slowly, they may produce less dramatic surface changes in the short term compared to AHA or BHA. This isn't necessarily a downside — for sensitive skin, slow and steady is often the more comfortable and sustainable approach — but it's worth setting expectations accordingly.
The most common ones you'll see on ingredient lists are glycolic acid, lactic acid, mandelic acid, and tartaric acid.
Side-by-Side Comparison
| AHA | BHA | PHA | |
|---|---|---|---|
| Solubility | Water-soluble | Oil-soluble | Water-soluble |
| Works mainly on | Skin surface | Inside pores | Skin surface (gently) |
| Best suited for | Dry, sun-damaged-looking, dull skin | Oily, congested, acne-prone skin | Sensitive, reactive skin |
| Common ingredients | Glycolic acid, lactic acid, mandelic acid | Salicylic acid | Gluconolactone, lactobionic acid |
| Typical feel on skin | Can tingle, especially glycolic acid | Can feel drying | Usually minimal sensation |
| Sun sensitivity concern | Higher | Moderate | Lower, but sunscreen still essential |
Choosing Based on Skin Type
If You Have Oily or Acne-Prone Skin
BHA (salicylic acid) is usually the starting recommendation because of its oil solubility and ability to work inside the pore. Some people with oily skin also layer in an AHA occasionally for surface texture, but it's generally best to introduce one active at a time and watch how skin responds before combining them.
If You Have Dry or Normal Skin
AHAs, particularly lactic acid, tend to be a comfortable fit since they can support smoother texture without the oil-focused action of BHA. Pairing an AHA with a hydrating moisturizer helps offset any dryness from the exfoliation process itself.
If You Have Sensitive or Reactive Skin
PHA is typically the gentlest entry point. If PHA is well tolerated over several weeks, some people cautiously introduce a low-percentage, buffered AHA like mandelic acid — but this should be a gradual process, and it's worth pausing at any sign of persistent redness or discomfort.
If You Have Combination Skin
Combination skin sometimes benefits from using different products in different areas — for example, a BHA-focused product on an oilier T-zone and a gentler PHA or AHA elsewhere — though this level of customization isn't necessary for everyone and can also be achieved with a single balanced formula.
How to Introduce a Chemical Exfoliant
Starting Frequency
Most guidance suggests starting with any new chemical exfoliant just once or twice a week, regardless of which type you choose, and observing how skin responds over a couple of weeks before increasing frequency. Skin needs time to adjust, and going too fast is one of the more common reasons people experience irritation and then give up on exfoliating acids altogether.
What to Avoid Combining
It's generally not advisable to layer multiple strong actives (like a high-percentage AHA and a retinoid) on the same night when you're new to a routine, since this can compound irritation. Many people find it works better to alternate nights or use one active in the morning and another in the evening, though everyone's tolerance is different.
Sunscreen Is Non-Negotiable
Because all three exfoliant types can increase how easily skin reacts to UV exposure — AHAs most notably — daily broad-spectrum sunscreen is an essential companion to any chemical exfoliation routine, not an optional add-on.
Common Mistakes to Watch For
- Using multiple exfoliating products at once (a cleanser, toner, and serum that each contain acids) without realizing the cumulative effect
- Skipping patch testing when trying a new formula, especially at higher concentrations
- Assuming a stronger percentage always means better results — more isn't automatically more effective, and it often just increases irritation risk
- Exfoliating on already compromised, sunburned, or freshly-irritated skin
- Discontinuing sunscreen because "it's already applied under makeup" — reapplication still matters
FAQs
Can I use AHA and BHA together?
Some formulas combine both, and some people alternate them on different days. Whether this suits your skin depends on tolerance and skin type — those with sensitive skin may find combining acids increases irritation risk, while more resilient skin types sometimes tolerate a combined approach well. It's generally safer to introduce one at a time first.
Which exfoliant is best for beginners?
PHA is often suggested as a starting point because it tends to feel gentler and cause less initial tingling or peeling. Lactic acid (an AHA) is another commonly recommended beginner option. Starting with lower frequency and observing your skin's response matters more than which specific acid you pick first.
Do chemical exfoliants replace physical scrubs entirely?
Not necessarily — some people still enjoy an occasional gentle physical exfoliant, though many dermatology-adjacent sources suggest chemical exfoliants are generally more even and less likely to cause micro-tears than abrasive scrubs. It comes down to personal preference and how your skin responds to each method.
How do I know if a chemical exfoliant is too strong for my skin?
Signs include persistent redness that doesn't fade within an hour or two, stinging that continues rather than fading quickly, flaking beyond mild and expected surface shedding, or increased breakouts. If you notice these signs, reducing frequency, lowering concentration, or switching to a gentler acid type like PHA is worth considering.
Can I use a chemical exfoliant every day?
Daily use isn't necessary or recommended for most people, especially with AHA or BHA. Many routines use exfoliating acids two to three times a week, adjusting based on how skin responds. PHA's gentler profile means some people tolerate more frequent use, but it's still worth easing in gradually.
Is PHA less effective than AHA or BHA?
PHA works more gradually and on a shallower level than AHA or BHA, which isn't the same as being ineffective — it simply has a different, gentler mechanism. For sensitive skin types, this slower approach is often the more practical and comfortable long-term choice, even if changes may be less immediately noticeable.
