Ingredient caution: vitamin C/ascorbic derivatives might cause tingling, redness or irritation in sensitive skin; rich oils, butters or occlusive emollients might feel heavy or clog pores in acne-prone/oily 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. Use a small amount first and avoid applying on active acne if it feels greasy. 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.