Ingredient caution: vitamin C/ascorbic derivatives might cause tingling, redness or irritation in sensitive skin; niacinamide is usually gentle but might cause tingling or flushing in very reactive skin; preservatives such as phenoxyethanol/benzyl alcohol might sting very sensitive or compromised 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. Start slowly if your skin is sensitive and avoid combining too many new actives at once. Do not apply on broken, freshly waxed or irritated skin. Apply on slightly damp skin and follow with moisturiser if dryness occurs. Stop use if irritation persists.