the.com/spf
A number promising your skin won't become a cautionary tale by 3pm.
means Sun Protection Factor measures how much longer sunscreen lets you stay in UV before burning compared to bare skin.
from Coined in 1974 by Austrian chemist Franz Greiter, building on his earlier 1962 sun-protection ratings born from a real sunburn on a mountain.
Diminishing returnsSPF 30 blocks 97 percent, SPF 50 only 98 percent.
UVB onlyThe number ignores UVA, the aging, deeper rays.
Reapply ruleIt expires roughly every two hours, sweat-accelerated.