Ingredient caution: salicylic acid/BHA might cause stinging, dryness, peeling, redness and increased sun sensitivity; niacinamide is usually gentle but might cause tingling or flushing in very reactive skin. Do a patch test before applying. First-time users should start 3–4 times a week, avoid using it with retinol or other exfoliating acids in the same routine, and apply sunscreen daily. Start slowly if your skin is sensitive and avoid combining too many new actives at once. Stop use if irritation persists.