Alpha-hydroxy acids (AHAs) and beta-hydroxy acids (BHAs) are exfoliating acids used to smooth texture, brighten tone, and keep pores clear. AHAs like glycolic, lactic, and mandelic acids are water‑soluble surface exfoliants that help with dullness, uneven texture, and fine lines. BHAs (salicylic acid) are oil‑soluble and excel at decongesting pores, making them a go‑to for blackheads and T‑zone congestion—common pain points for combination, blackhead‑prone, and sensitive skin when used carefully.

How they work: AHAs loosen the bonds (desmosomes) between dead skin cells in the stratum corneum, accelerating natural shedding and improving light reflection for glow, while encouraging epidermal renewal over time. Glycolic (smallest molecule) penetrates the most and is the most potent/irritating; lactic adds humectant hydration; mandelic (largest) is the gentlest and a favorite for reactive skin. BHAs like salicylic acid penetrate into oily pores to dissolve debris, reduce microcomedones, and calm redness thanks to their anti‑inflammatory profile. For best efficacy, leave‑on formulas are typically pH‑adjusted (~pH 3–4). Want to tailor acids to your exact skin type? Start by discover your skin type.

How to Use It

Targets and strengths: For blackheads and combination T‑zones, BHAs at 0.5–2% in leave‑on formats are most effective. Choose 0.5–1% if sensitive; 2% if you’re tolerant and primarily fighting persistent blackheads. For tone/texture and dullness on normal‑to‑dry areas, AHAs at 5–10% (lactic or mandelic for sensitivity; gentle glycolic if you’re experienced) work well as 2–4x weekly leave‑ons. Weekly treatments at 10–15% can be used by advanced users; avoid this range if you’re reactive until your barrier is robust.

Frequency and placement: Start low and slow—2–3 nights per week—then increase as tolerated. With combination skin, try zone application: BHA on the T‑zone for blackheads and oil control; AHA on cheeks where texture and glow need help. Alternatively, alternate nights (e.g., BHA Monday/Thursday; AHA Tuesday/Saturday). Cleansers with salicylic or AHA are great primers for oil control but have short contact time; for stubborn blackheads, leave‑on BHA is superior.

Layering and pairings: Apply acids after cleansing on dry skin; follow with a hydrating toner or serum, then moisturizer. Pair with barrier‑friendly actives—niacinamide, panthenol, centella, beta‑glucan, and ceramides—to buffer irritation. If using retinoids, alternate nights rather than layering to reduce sensitivity. Be cautious combining with benzoyl peroxide in the same routine if easily irritated; staggering applications prevents over‑exfoliation. Pure L‑ascorbic acid vitamin C (low pH) may compound sting; consider using C in the morning and acids at night. Always finish AM routines with broad‑spectrum SPF 30+—acids increase photosensitivity.

What to expect: Mild tingling is common initially; tightness or flaking signals you should scale back frequency, buffer with moisturizer, or switch to gentler acids (mandelic or lactic) or a lower BHA strength. Temporary purging (accelerated turnover revealing pre‑existing clogs) may occur for 2–4 weeks with leave‑on acids; widespread irritation, burning, or prolonged redness is a sign to stop and rebuild the barrier.

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Who Should Avoid It

Proceed with caution if you have a compromised barrier, eczema, perioral dermatitis, or a rosacea flare—acids can aggravate stinging and redness. Those with an aspirin (salicylate) allergy should avoid BHA. If you’re pregnant or breastfeeding, low‑strength, small‑area use of topical salicylic acid is generally considered acceptable by many dermatologists, but skip high‑strength peels and confirm with your clinician. Pause acids for 5–7 days after waxing, microneedling, or in conjunction with strong prescription retinoids until your provider clears you.

Start slowly, listen to your skin, and adjust frequency before strength. Build a routine that balances exfoliation with barrier support and daily SPF. Not sure which acid and strength fits your exact skin type? Visit skinguide.beauty to find the right ingredients and routine for your skin.