What it does
Glycolic acid has the smallest molecular size of the common alpha hydroxy acids, which means it penetrates fastest and works hardest — on surface texture, dullness and uneven tone. It also means it stings more and is the acid most likely to push skin too far.
It increases sun sensitivity meaningfully, so it is an evening ingredient and it makes daily sunscreen non-negotiable rather than merely advisable.
If glycolic acid is too much, lactic acid does a similar job more gently and adds hydration, and mandelic acid is gentler still. There is no prize for using the harshest option.
In a routine
Layers well with
- Hyaluronic acid
- Ceramides
- Niacinamide
Do not layer with
- Retinol
- Salicylic acid
- Vitamin C
Same routine is fine for some pairs — same step is the problem. Split them morning and evening when in doubt.
