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; fragrance, essential oils or fragrance allergens might trigger redness, itching or allergic irritation; preservatives such as phenoxyethanol/benzyl alcohol might sting very sensitive or compromised skin. 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. Avoid this product if you have fragrance allergy, eczema-prone skin or a damaged barrier. Do not apply on broken, freshly waxed or irritated skin. Stop use if irritation persists.