Three acids, similar names, very different jobs. Choosing the wrong one is why a lot of people conclude that chemical exfoliation "doesn't work" or "irritates my skin."
The short version
- AHA works on the surface. For dullness, rough texture, and uneven tone.
- BHA works inside the pore. For blackheads, congestion, and acne.
- PHA works gently on the surface. For sensitive skin that cannot tolerate the other two.
AHA: alpha hydroxy acid
Water-soluble, so it stays on the surface and dissolves the bonds holding dead skin cells together.
The common types are glycolic acid, the smallest molecule and the strongest, and lactic acid, larger, gentler, and also hydrating.
Use it for: dull skin, rough texture, fine lines, uneven tone, and sun damage.
Not ideal for: active acne or blackheads, since it cannot get into the pore.
AHAs increase sun sensitivity noticeably. In Sri Lanka that means night use only and strict sunscreen the next morning.
BHA: beta hydroxy acid
Salicylic acid, and its distinguishing feature is that it is oil-soluble. That means it can travel through sebum into the pore and clear the plug from inside. Nothing else over the counter does this.
Use it for blackheads, whiteheads, congestion, acne, oily skin, enlarged-looking pores.
Not ideal for: dry skin with no congestion, where an AHA suits better.
Korean formulas typically use 0.5 to 2 percent, designed for regular use rather than occasional strong treatments. BHA is also mildly anti-inflammatory, which is why it suits inflamed acne where AHA can aggravate.
PHA: polyhydroxy acid
Gluconolactone and lactobionic acid. Chemically similar to AHA but with much larger molecules, so they penetrate more slowly and irritate far less. They are also humectants, meaning they hydrate while they exfoliate.
Use it for: sensitive or reactive skin, rosacea-prone skin, first-time exfoliation, or any skin that stings with AHA and BHA.
Trade-off: gentler results, more slowly. That is usually the right trade.
PHA is the most under-used of the three and the one most people should start with.
Which one do you need?
| Your concern | Choose |
|---|---|
| Blackheads on nose and chin | BHA |
| Dull, rough, uneven skin | AHA |
| Active breakouts | BHA |
| Fine lines and sun damage | AHA |
| Sensitive skin, any concern | PHA |
| Oily T-zone, dry cheeks | BHA on T-zone, AHA elsewhere |
| Never exfoliated before | PHA |
How often
Start at two to three times a week, at night. Build up only if there is no tightness, redness or stinging.
Low-strength PHA toners can go daily for many people. AHA and BHA are usually better every other night at most. Daily use of a strong acid is the most common cause of the damaged barriers we hear about.
More is not faster. Over-exfoliated skin becomes red, tight, shiny in a way that is not healthy, stings with products that used to be fine, and paradoxically breaks out more.
What not to combine
- Two acids on the same night. Pick one.
- Acid and retinol on the same night. Alternate them instead.
- Acid and a physical scrub. Ever.
- Acid and vitamin C in the same routine if your skin is at all sensitive. Morning C, evening acid.
The old rule about waiting 30 minutes between acid and other products was based on outdated formulation science and is not necessary with modern Korean products. Layer normally.
Toner, serum, or cleanser?
Cleanser: gentlest, because it rinses off. Good for daily use and for starting out.
Toner: the middle ground and the most popular format. Leave-on, low strength, suitable for a few times a week.
Serum: strongest. Two or three nights a week maximum.
Do not use all three in one routine. That is three exfoliating steps, not one.
The sunscreen rule
All three make your skin more sensitive to UV, AHA most of all. Exfoliating without daily sunscreen actively causes the pigmentation you are probably trying to treat. In a country with an extreme UV index, this is not a minor footnote.
Browse AHA and BHA products, exfoliating toners, or salicylic acid for congestion.
