The short answer
Salicylic acid (BHA) and glycolic acid (AHA) both exfoliate, but they aim at different problems: BHA is oil-soluble and useful inside congested pores; glycolic is a small AHA that hits surface texture and dullness hardest. Using strong leave-on versions together is double exfoliation, not double results.
The library lists each under the other’s avoidWith for that reason. “Acid stacking” marketing skips the part where your barrier starts stinging on cleanser alone.
Choose by goal for a given night. Blackheads and congestion → salicylic. Surface roughness and tone → glycolic (if you tolerate it). Many people only need one acid family at a time.
Honest cosmetic-use guidance for home routines. Stop and seek a professional if you get swelling, blistering, or symptoms that worry you.
How to use both without stacking them
- BHA nights: leave-on salicylic acid → moisturiser. No glycolic acid.
- AHA nights: glycolic acid → moisturiser. No salicylic leave-on.
- Two to three exfoliant nights a week total is enough for most skin — not two to three of each.
- Sunscreen every morning. Both increase sun sensitivity.
