AHA & BHA Exfoliating Serums: The Complete Guide

What chemical exfoliation does to dead skin cells

Skin naturally sheds dead cells from its surface. That process slows down over time. It can leave a build-up of dull, rough, uneven texture sitting on top of healthier skin underneath. Chemical exfoliants - AHAs and BHA - speed up that shedding. They dissolve the bonds between dead skin cells, rather than physically scrubbing them off with a brush or granules. The action happens at a cellular level, not through friction. Well-formulated acid exfoliants tend to be gentler on the skin's surface than a harsh physical scrub, even though the word acid sounds more aggressive.

AHA: glycolic acid, lactic acid & mandelic acid for surface renewal

Alpha-hydroxy acids are water-soluble. They work primarily on the outermost layers of skin. The two most common in facial serums are glycolic acid and lactic acid. Glycolic acid is derived from sugar cane. It has the smallest molecular size of the group, which lets it penetrate fastest and typically deliver the most visible brightening. Lactic acid is a slightly larger molecule. It's generally considered milder and pairs a mild humectant effect with its exfoliating action. Mandelic acid, a larger and gentler AHA derived from almonds, is worth knowing too. It's often recommended for people with deeper skin tones, since it carries a lower risk of triggering post-inflammatory hyperpigmentation.

AHAs are generally the better fit for concerns that live on the surface: dullness, rough texture, uneven tone, and fine surface lines. They're less targeted at active oiliness or clogged pores, since they don't travel into the pore lining the way an oil-soluble acid does.

BHA (salicylic acid): the pore-clearing acid for blackheads & clogged pores

Salicylic acid is the BHA used in virtually every facial exfoliating product on the market. Unlike AHAs, it's oil-soluble. That lets it travel past surface oil and into the pore itself. This is why it's the go-to ingredient for blackheads, closed comedones, and general congestion in oily or combination skin. Salicylic acid also has some anti-inflammatory properties, which is part of why it's a common ingredient in acne-focused routines. It tends to be less effective than AHAs at surface brightening, since its strength is working inside the pore rather than smoothing the top layer of skin.

PHA & gluconolactone: the gentle option for sensitive skin

Polyhydroxy acids (PHAs) like gluconolactone and lactobionic acid work similarly to AHAs. They have larger molecules, so they penetrate more slowly and tend to cause less irritation. They're a reasonable middle ground for sensitive skin that's found AHAs or BHA too reactive, or for anyone exfoliating for the first time.

Matching acids to dullness, texture, dark spots & hyperpigmentation

• Oily or acne-prone skin: lead with BHA. It addresses the pore congestion that's usually driving the breakouts, in a way AHAs can't.
• Dry, dull, or textured skin without much oiliness: an AHA - glycolic for faster, more noticeable results if your skin tolerates it, lactic or mandelic if you want something gentler.
• Dark spots or hyperpigmentation: a consistent AHA routine paired with daily sunscreen does the most to fade discoloration over time.
• Sensitive, reactive, or newly-exfoliating skin: start with a PHA or a low-percentage lactic acid, used once or twice a week, before working up to anything stronger.
• Combination skin: a light AHA/BHA blend, or alternating a BHA on oilier nights with an AHA on drier ones, usually works better than trying to find one product that does everything.

Widely available options span both budget and prestige price points - brands like Paula's Choice, The Ordinary, COSRX, Good Molecules, and Sunday Riley all make well-reviewed AHA and BHA formulas.

Fitting AHA & BHA into a routine without overdoing it

Exfoliating acids are typically applied after cleansing and before moisturizer, on skin that's dry rather than damp. For a first-time user, two to three nights a week is a reasonable starting cadence. Watch for excess redness, stinging that doesn't fade within a minute or two, or visible flaking over the following days. Tolerance builds over several weeks. Frequency can be increased gradually from there, but more isn't automatically better - many people get their best results settling at three to four nights a week rather than using an acid nightly.

It's worth being deliberate about what else is in the routine on acid nights. Stacking an exfoliating acid with a retinoid on the same night is one of the most common causes of visible irritation, since both ingredients increase skin cell turnover. Many people alternate instead - acids on some nights, retinoid on others. Anyone using a prescription-strength retinoid, or being treated for a specific skin condition, should check with their prescribing provider before adding an exfoliating acid into the mix.

Sunscreen, retinol & protecting your skin barrier

Exfoliating acids increase how easily skin burns and how visible sun damage becomes, because they're removing the outer layer of cells that offers some baseline protection. Daily broad-spectrum sunscreen isn't a suggestion alongside an acid routine - it's the difference between the brightening results holding and being undone by unprotected sun exposure. This matters just as much on cloudy days and in winter as it does in summer.

When oily skin, breakouts, or irritation need a dermatologist

Mild tingling on first application, and occasional light flaking in the first couple of weeks, are common and not necessarily a sign anything is wrong. Ongoing burning, spreading redness, breakouts that get worse rather than better, or any reaction that doesn't settle down after a few days of stepping back to a lower frequency are signs to stop. Check in with a dermatologist rather than trying to push through it or add more products to compensate. This is especially true for anyone with rosacea, eczema, or a diagnosed skin condition. An over-the-counter acid serum is not a substitute for a treatment plan from a qualified provider, and persistent or worsening symptoms should always be evaluated by one.