Two kinds of damage. UVB is absorbed by the DNA in your skin cells and snaps the code; the breaks that don't repair cleanly are how skin cancer starts. UVA goes deeper and chews through collagen over years, which is the wrinkles, the leather, and the brown blotches ¹. A broad-spectrum product blocks both; a bare SPF number only covers UVB.

Most face products have no hard proof; this one does. In subtropical Queensland, 1,621 fair-skinned adults applied SPF 16 every morning or used sunscreen however they liked. The daily group had 39% fewer squamous-cell carcinomas at four and a half years and no measurable photoaging on the back of the hand under blinded scoring ^{2 3}. Ten years on, they had half the melanoma rate of the other group ⁴. All of that from SPF 16, on head and arms only.

The habit is small; the dose is the whole game. The label number assumes 2 mg per square centimetre — a heaped teaspoon for face and neck. Almost nobody applies that much ⁵, so you buy headroom two ways: pick SPF 30 or higher, and reapply on days you stay outside.

Cheap works; texture decides whether you actually wear it. A drugstore tube of CeraVe or Neutrogena covers a month of face-and-neck use, and a year runs from thirty dollars up. What makes you quit by week three is a product that pills, stings, or leaves a white cast. Tinted mineral formulas add iron oxides that block visible light too, which matters for melasma and for darker skin where pigmentation is the main reason to wear it ⁸.

The comfort lands this week; the real dividend takes decades. Within a week: no end-of-day tightness across the cheeks, no peeling nose. Within months: no rim of pink in beach photos. Across years: the brown spots on the backs of your hands stop multiplying. The dermatologist's demonstration is the inside of your upper arm against the back of your hand — same age, one hidden from the sun and one not, and by your fifties the arm reads fifteen years younger ⁹. Roughly 80% of a face looking old is built that way ¹⁰.