AHA or BHA? Which acid for which skin

Exfoliating acids are where a lot of people either transform their skin or wreck their barrier, and the difference usually comes down to picking the wrong type or using too much of the right one. The two families, AHAs and BHAs, do related jobs in different places. Knowing which is which tells you most of what you need.

Same idea, different territory

Both dissolve the glue holding dead cells together so they shed instead of piling up. The split is about where they work.

• AHAs (glycolic, lactic, mandelic) are water-loving. They work on the surface of the skin, loosening dull, rough, dry-looking cells. Think tone, texture, and glow.
• BHAs (salicylic acid is the one that matters) are oil-loving. They dissolve into the pore itself and clear out the oil and debris that cause congestion and breakouts.

That single trait, water-soluble versus oil-soluble, is the whole decision. If your problem sits on the surface, reach for an AHA. If it sits inside the pore, reach for a BHA.

Surface problems want an AHA. Pore problems want a BHA.

Which AHA

They are not interchangeable. Molecule size changes how deep and how aggressively they go.

• Glycolic is the smallest, so it penetrates fastest and does the most, for brightness and fine lines, but it is also the most likely to sting.
• Lactic is larger and gentler, and it hydrates as it exfoliates. A good starting point for dry or sensitive skin.
• Mandelic is the largest and slowest, which makes it the calmest option and a friend to reactive or deeper skin tones prone to marks.

When to pick BHA

Salicylic acid earns its place if you have blackheads, whiteheads, closed bumps, an oily T-zone, or breakouts. Because it is anti-inflammatory and gets inside the pore, it also calms angry spots in a way AHAs cannot. Oily and acne-prone skin usually gets more from a BHA than an AHA.

Many people do best with both: a BHA for congestion, an AHA for glow, on different days.

How to use them without overdoing it

The mistake is almost never the acid. It is the frequency.

• Start twice a week, at night, one acid at a time, and build up only if your skin stays comfortable.
• Low percentages work. A 5 to 8% lactic or a 2% salicylic does the job. Chasing 30% peels at home is how barriers break.
• Never layer acids on the same night as retinoids when you are starting out. The combined stripping is too much.
• SPF every morning, no exceptions. Fresh exfoliation leaves skin more sun-sensitive.
• If it stings, flakes, and tightens, that is too much, not "working". Pull back.

What to do this week

If you are choosing your first acid, match it to your main complaint. Dull, rough, uneven tone points to a gentle lactic AHA. Congestion, oil, and breakouts point to a 2% salicylic BHA. Use it twice a week for the first fortnight, keep the rest of your routine simple, and let your skin set the pace. One well-chosen acid used sparingly beats a shelf of them used all at once.