Retinoic acid itself — no conversion needed, so it is the strongest and fastest-acting retinoid.
Tretinoin is the reference standard against which every other retinoid is measured. Because it is already in its active form, it does not need to be converted by the skin, which makes it both more effective and more irritating than retinol. It is prescription-only in most countries and should be used under medical supervision.
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.
Same reason as with AHAs — tretinoin does not need help exfoliating.
Leave the BHA out while you are on tretinoin.
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.