What's the safest way to add a new active to my routine as a beginner?

Introduce one new active at a time, so that if something stings or reddens you can tell which product caused it. Patch-test first — especially on sensitive or reactive skin — then start with infrequent use (for example every other day) and build up slowly as your skin adjusts. Support the barrier alongside it with calmer ingredients like niacinamide, ceramides or hyaluronic acid, and give a new retinoid or acid a short grace period for mild dryness or flaking before deciding it doesn't suit you. The concentration that matters is in the app. If you are pregnant, breastfeeding, or have a known allergy, check with a doctor before adding anything new. This is cosmetic reference for appearance and formulation, not medical advice.