Stacking the wrong active ingredients in one session can leave you with less benefit and more irritation than using nothing at all. The good news: almost every "conflict" is solved by timing, not by giving up the ingredient.
The big ones to avoid layering
- Retinoids + benzoyl peroxide — benzoyl peroxide oxidises many retinoids and cancels their effect. Use benzoyl peroxide in the morning and your retinoid at night, or on alternate days.
- Retinoids + exfoliating acids (AHA/BHA) — both speed cell turnover, so together they over-exfoliate. Alternate nights instead of layering.
- Vitamin C + exfoliating acids — two low-pH actives can destabilise each other and sting. Keep vitamin C in the AM and acids at night.
- Multiple exfoliating acids at once — one AHA or BHA per session is plenty; stacking them is the fastest route to a damaged barrier.
What actually plays nicely
Niacinamide is the easy one — it layers with almost everything, including vitamin C (the old "they cancel out" claim is largely a myth with modern formulas). A simple, conflict-free template looks like:
- AM: gentle cleanser → vitamin C → moisturiser → SPF
- PM: gentle cleanser → one treatment (retinoid or an acid, not both) → moisturiser
Let the tool do the checking
Rather than memorise a chart, build your routine and let it flag conflicts for you. regimen's ingredient-conflict checker reads the actives in every product you add and warns you in real time — with a plain-English fix for each clash. It works on thousands of real products, so you can check what's actually on your shelf.