What is the difference between physical and chemical sunscreen?

Physical sunscreens — also called mineral sunscreens — use zinc oxide or titanium dioxide to create a barrier that sits on the skin’s surface and reflects both UVA and UVB rays away. They start working the moment you apply them, are less likely to irritate sensitive or rosacea-prone skin, and the FDA recognizes both active ingredients as safe and effective. The downside: they tend to be thicker, harder to rub in, and can leave a visible white or chalky cast, especially on darker skin tones.

Chemical sunscreens use organic compounds — oxybenzone, avobenzone, octisalate, octocrylene, and others — that absorb into the top layer of skin and convert UV radiation into heat, which then dissipates. They’re generally lighter, spread more easily, and disappear without a trace, which makes them popular for daily wear under makeup. The trade-offs: they need about 15 to 20 minutes to become effective after application, some ingredients (especially oxybenzone) can irritate sensitive skin, and certain chemical filters have been banned in places like Hawaii and Key West because of their impact on coral reefs.

Neither type is universially better. Physical sunscreens are the safer starting point for sensitive skin, babies, and people with melasma. Chemical sunscreens win on texture and wearability, especially for sports and swimming where you want something that stays put without streaking. Plenty of modern formulations blend both types. What matters more than which kind you pick is that you actually use it — broad spectrum, SPF 30 or higher, reapplied every two hours.