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UV Science Basics

Why Sunscreen Is the Cheapest Anti-Aging Product You'll Buy

A $15 bottle outperforms a $150 serum for aging.

By the numbers

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.
What the evidence shows

Frequently asked questions

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.

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.

What people are asking

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 ↗

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