Ingredient caution: vitamin C/ascorbic derivatives might cause tingling, redness or irritation in sensitive skin; high-strength niacinamide might cause flushing, tingling or small bumps in reactive skin; humectants such as hyaluronic acid/glycerin are usually gentle but might feel sticky or tight if not sealed with moisturiser. Do a patch test before applying. First-time users should start 3–4 times a week and avoid layering with strong exfoliating acids if the skin stings. First-time users should start 3–4 times a week and reduce frequency if redness or bumps appear. Apply on slightly damp skin and follow with moisturiser if dryness occurs. Avoid during pregnancy or breastfeeding unless your doctor approves. Stop use if irritation persists.