SPF 30 blocks roughly 97% of UVB rays. SPF 50 blocks about 98%. The jump from 30 to 50 isn't dramatic — but how much you apply matters far more than the number on the bottle.
The two-finger rule
Squeeze sunscreen along the length of your index and middle fingers. That's the amount for face and neck. Most people use a fraction of that.
UVA vs. UVB
UVB causes burning. UVA causes aging and penetrates clouds and windows. "Broad spectrum" or a high PA rating (PA+++ or PA++++) indicates UVA protection.
Reapplication
Every two hours of sun exposure, or after swimming and sweating. Powder and stick sunscreens make midday top-ups practical over makeup.
