How Sunscreen Actually Works (Absorb vs Reflect)
The chemical vs mineral mechanism, minus the fearmongering.
Up to 80% of UV rays can penetrate cloud cover on an overcast day.
Visible light makes up about 45% of sunlight and can worsen pigmentation in deeper skin tones.
Frequently asked questions
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.
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.
r/SkincareAddiction: 'Does UV actually come through car windows?'
Sources & citations
- WHO, 'Global Solar UV Index: A Practical Guide' (World Health Organization, 2002)
- today.ucsd.edu ↗