Actives glossary
Glycolic acid
The smallest AHA, which is why it penetrates fastest and stings most.
- INCI name
- Glycolic Acid
- Also called
- AHA, alpha hydroxy acid
- Family
- Acid
- Range seen on labels
- 5% to 10% for leave-on cosmetic use
- Sits well with
- ceramides, niacinamide
- Needs care with
- retinol, retinaldehyde, salicylic-acid
Glycolic acid has the smallest molecule of the common alpha hydroxy acids, so at the same percentage and pH it penetrates further and faster than lactic or mandelic acid. That is the reason it produces results sooner and the reason it stings more.
Percentage without pH is half a number
An AHA’s activity depends on how much of it is in its free acid form, which depends on the pH of the formula. A 10% glycolic at pH 4.5 is a milder product than a 7% at pH 3.5. Almost no brand publishes a pH, which makes the percentage on the front of the bottle an incomplete figure by itself.
Sun
AHAs increase sun sensitivity for about a week after use. This is on the label of most products because United States labelling rules require it, and it is one of the few label statements in skincare that is both mandatory and useful.