UVA vs UVB, Explained Like You're Scrolling at 2AM
The single most useful thing to understand about sun damage, in 60 seconds.
About 95% of UV radiation reaching the ground is UVA; only ~5% is UVB.
Dermatologists summarize it simply: UVB causes the burn, UVA drives the aging.
Questions we get a lot
What is the difference between UVA and UVB rays?
UVB rays have shorter wavelengths and cause sunburn, affecting mainly the skin's surface; UVA rays penetrate deeper and drive premature aging, wrinkles and pigmentation. About 95% of the UV reaching the ground is UVA. Both damage DNA and contribute to skin cancer, which is why 'broad-spectrum' protection against both matters.
Does UV come through windows and clouds?
Largely, yes. Standard glass blocks most UVB but lets UVA through, so windows at home, in the office, or a car's side windows still expose skin to aging rays (laminated windshields block most UVA). Clouds stop only a fraction of UV, so protect skin near windows and on overcast days.
r/SkincareAddiction: 'Do I really need SPF if I'm inside all day near a window?'