AHA and BHA are the two families of exfoliating acids you'll see on practically every serum and toner shelf, and picking the wrong one for your skin is one of the most common routine mistakes we see. The short version: AHAs work on the surface and suit dry or dull skin, BHA works inside the pore and suits oily or breakout-prone skin. Here's the longer version, so you can choose with confidence.
What is an AHA?
AHA stands for Alpha Hydroxy Acid, a group of water-soluble acids originally derived from sources like sugar cane, milk and fruit. The ones you'll actually meet on labels are glycolic acid (the strongest and most researched), lactic acid (gentler) and mandelic acid (gentlest, good for sensitive skin).
AHAs work by loosening the bonds holding dead skin cells to the surface, so they shed properly instead of piling up and making your skin look dull and rough. Because they're water-soluble, they stay on the surface layers, which is exactly where dryness, rough texture and mild sun damage live. They're also humectants to a degree, particularly lactic acid, so they're more forgiving on skin that isn't oily.
Best for: dull, dry, rough or sun-damaged skin, uneven tone, and texture.
What is a BHA?
BHA is Beta Hydroxy Acid, which in skincare means one ingredient: salicylic acid. The crucial difference is that it's oil-soluble, so rather than sitting on the surface, it dissolves its way through sebum and gets inside the pore, clearing out the mix of oil and dead cells that becomes blackheads and breakouts.
Salicylic acid is also naturally anti-inflammatory (it's chemically related to aspirin), which is why it calms angry red blemishes rather than aggravating them. That combination of pore-clearing and soothing is why it's the default recommendation for oily and acne-prone skin.
Best for: oily skin, blackheads, clogged pores, breakouts and enlarged pores.
The key differences at a glance
- Solubility: AHAs are water-soluble and work on the surface. BHA is oil-soluble and works inside the pore.
- Skin type: AHAs favour dry and normal skin. BHA favours oily and combination skin.
- Main job: AHAs brighten and smooth. BHA unclogs and calms.
- Irritation: both can irritate if overused, but BHA at 2% is generally the more forgiving daily option, while stronger AHAs (glycolic 7%+) deserve more respect and a slower introduction.
Can you use both together?
You can, but most people shouldn't use them at the same time. Layering an AHA and a BHA in one session is a fast track to a damaged skin barrier, and it's one of the combinations we flag in our ingredients you shouldn't mix guide. If your skin genuinely benefits from both, alternate: BHA a couple of nights a week for congestion, an AHA once or twice a week for brightness, never on the same night.
If you have combination skin, another sensible approach is zoning: BHA on the oily T-zone, AHA on drier areas.
How to use them without wrecking your skin
- Start low: glycolic around 5-7%, salicylic at 2%, lactic at 5-10%.
- Start slow: once or twice a week, building up only if your skin stays comfortable.
- Use them at night, and patch test first.
- Wear SPF 30+ every morning without exception. Both acids increase sun sensitivity, and skipping sunscreen while using them undoes the benefit entirely.
- Watch for the signs of over-exfoliation: tightness, stinging under products that never used to sting, and unexplained shine.
To sum it up
AHA for surface concerns (dullness, dryness, texture, tone), BHA for pore concerns (oil, blackheads, breakouts). If you're torn, pick based on your biggest single concern, run it consistently for six to eight weeks, and resist the urge to stack acids. One well-chosen exfoliant used sensibly will beat a bathroom shelf full of them every time.