Ingredient caution: retinol/retinoids might cause dryness, peeling, redness, purging and sun sensitivity; 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. Do a patch test before applying. Retinol is not advised for pregnant or breastfeeding women unless approved by a doctor. First-time users should start 3–4 times a week at night, avoid layering with exfoliating acids, and use sunscreen daily. 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. Stop use if irritation persists.