Sunscreen (Skincare)

Sunscreen is the one product with strong evidence behind its cosmetic claims, and it works by filtering ultraviolet light before that light reaches skin. Two numbers matter: SPF measures protection from UVB, the burning wavelength. Broad spectrum on the label means UVA, the aging and pigmenting wavelength, is covered too. High SPF with no broad spectrum claim leaves half the job undone.

Filters come from two families that behave differently on skin. Mineral filters, zinc oxide and titanium dioxide, sit on the surface and scatter light. They work the moment they land and can leave a white cast on deeper tones. Chemical filters absorb light and convert it to heat, making them cosmetically invisible, though they need roughly fifteen minutes to settle into an even film. Water resistance is rated in minutes, either forty or eighty, and once that time in water passes the film is gone regardless of the SPF printed on the tube.

SPF inside a moisturizer undermines the whole idea, because people spread moisturizer thin while sunscreen needs a thick layer. The number on the bottle is rarely the number on your face. Foundation with SPF repeats that problem in a worse form. Retinoids need sunscreen more than any other active does, since the fresh skin they bring up is more light-sensitive, and using one without daily protection wastes the retinoid entirely.

Anyone with skin exposed to daylight needs it every day, cloudy weather included, since UVA passes through both cloud and window glass. Deeper skin tones are usually better served by chemical or modern hybrid filters, because mineral formulas cast gray. Acne-prone skin does better with fluid and gel textures than with heavy creams. Babies under six months belong in shade and clothing instead of sunscreen, and anyone treating pigmentation has more to lose from skipping it than anyone else.

Amount is where nearly everyone fails: a face needs about a quarter teaspoon, roughly two finger lengths of product squeezed along the index and middle fingers, and the neck wants the same again. Reapply every two hours in real sun and after swimming or toweling off, and a powder or stick over makeup beats skipping the reapplication. Filters degrade over time, so respect the expiration date, and never leave a bottle in a hot car, where heat breaks the emulsion and the protection with it.