What Causes a Sunburn at the Cellular Level
Inflammation, DNA damage, and that delayed redness, explained.
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.
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/SkincareAddiction: 'Do I really need SPF if I'm inside all day near a window?'
Sources & citations
- EPA, 'A Guide to the UV Index' (U.S. Environmental Protection Agency, 1994/updated)
- epa.gov ↗