Glycolic Acid
The smallest AHA, which makes it the most penetrating and the most likely to sting.
Glycolic acid loosens the bonds holding dull, dead cells to the surface of the skin. Its small molecular size means it penetrates further than lactic or mandelic acid, which is why it delivers faster results on texture and radiance — and why it is also the most irritating of the group. It raises sun sensitivity meaningfully, so daily sunscreen is not optional alongside it.
Night only, two or three times a week. If your skin is reactive, choose lactic or mandelic acid instead.
Retinol and glycolic acid are both doing turnover work on the same skin.
Alternate nights rather than layering them.
Both are low-pH actives, and using them together raises the odds of stinging without adding benefit.
Vitamin C in the morning, acids at night.
Two exfoliating acids at once is the fastest way to over-exfoliate.
Pick one as your main exfoliant. If you want both, use them on different nights.
Prescription tretinoin is already at the limit of what most skin tolerates; adding an AHA reliably damages the barrier.
Drop the acid while you are using tretinoin, and speak to your prescriber before reintroducing it.
skinfrndly is educational and is not medical advice. Recommendations are generated from the answers you gave and general dermatological guidance — they cannot account for your full history. For persistent or severe skin conditions, or before starting anything new during pregnancy, speak to a doctor or dermatologist.