UV intensity rises roughly 4-5% for every 1,000 feet of elevation gain.
UC San Diego's Dr. Y. Linda Liou advises sun protection whenever the UV index is 3 or higher.
Questions we get a lot
How does UV light age and damage skin?
UVB is absorbed by DNA in surface cells, causing direct mutations that can lead to skin cancer. UVA penetrates deeper, generating free radicals that damage DNA, collagen and elastin — producing wrinkles, sagging and dark spots. The damage accumulates over a lifetime, so daily protection pays off.
What does the UV index mean and when should I protect my skin?
The UV Index, from the EPA and WHO, rates the strength of midday UV on a scale from 1–2 (low) to 11+ (extreme). Dermatologists generally advise sun protection whenever it reaches 3 or higher. It appears in most weather apps and rises with sun elevation, altitude and proximity to the equator.
r/SkincareScience: 'Can someone explain UVA vs UVB like I'm five?'