Alpha Hydroxy Acids (AHAs): What They Are and How to Use Them

“AHA” is one of those acronyms that shows up everywhere in skincare without much explanation. Alpha hydroxy acidsare a whole family of surface-exfoliating acids — and once you know the differences between them, choosing the right one for your skin is simple. Here’s the plain-English version.

What AHAs are

Alpha hydroxy acids are water-solubleacids derived from foods like fruit, sugar cane and milk. Because they’re water-soluble, they work on the skin’s surface, dissolving the bonds that hold dull, dead cells in place so they shed more evenly. The result is smoother texture, brighter tone and a fresher look. That surface action is the key difference from a BHA (salicylic acid), which is oil-soluble and works inside pores instead.

The AHA family, gentlest to strongest

• Mandelic acid— the largest molecule, so the slowest and gentlest. The go-to for very sensitive skin and deeper skin tones, with mild antibacterial benefits for breakouts.
• Lactic acid— a mid-size molecule that’s gentle and, uniquely, hydrating. Ideal for dry and sensitive skin that wants smoothing without the sting.
• Glycolic acid— the smallest molecule, so the deepest-penetrating and most potent. Best for resilient skin chasing stubborn texture, dullness and glow — but the easiest to overdo.

You’ll also see citric, tartaric and malicacids on labels; they’re AHAs too, often used in smaller supporting roles. The three above are the ones that carry a routine.

What AHAs do

• Smooth texture by shedding dull surface cells.
• Brighten and even out tone over consistent use.
• Soften the look of sun damage and fine lines with regular use.
• Hydrate (lactic acid specifically) as they exfoliate.

What they don’t do is clear oily, congested pores — for blackheads and breakouts, reach for salicylic acid instead.

Which AHA should you choose?

Sensitive or reactive skin → mandelic. Dry skin, or a cautious beginner → lactic. Resilient skin wanting stronger, faster results → glycolic. There’s no prize for jumping straight to the strongest — starting gentle and stepping up is the smart, low-risk path.

How to use them safely

The rules are the same across the family. Introduce one AHA at a time, start at two or three nights a week, and build up only as your skin stays comfortable. Always follow with a moisturizer, and always wear daily sunscreen— AHAs raise sun sensitivity for about a week. Don’t stack an AHA with a retinoid or another acid on the same night, and watch for the signs of over-exfoliation (stinging, redness, tightness, flaking), which mean you should ease off. When you’re ready to buy, our best chemical exfoliants roundup compares real AHA and BHA products by type, and our how often to exfoliate guide helps you set the right cadence.