Why Your Phone's Weather App Knows the UV Index
How UV forecasting actually works.
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.
Frequently asked questions
Is visible light bad for skin?
Visible light makes up about 45% of sunlight. Research shows high-energy visible (blue) light can worsen pigmentation and melasma, especially in medium-to-deep skin tones. Tinted sunscreens containing iron oxides help shield against it, which clear sunscreens generally do not.
How does sunscreen actually work?
Sunscreens use UV filters in two groups. Organic ('chemical') filters such as avobenzone absorb UV and release it as a small amount of heat. Mineral ('physical') filters — zinc oxide and titanium dioxide — mainly absorb UV and also scatter some. Both cut how much UV reaches living skin cells.
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.
r/SkincareScience: 'Can someone explain UVA vs UVB like I'm five?'
Sources & citations
- Sklar LR et al., 'Effects of ultraviolet and visible radiation on the skin,' Photochem Photobiol Sci, 2013
- skincancer.org ↗