How Much UV Does Glass Block? (Office, Car, Home)
A window-by-window breakdown of what glass really blocks.
The UV Index scale runs from 1-2 (low) to 11+ (extreme); protection is advised above 3.
Since roughly 95% of the UV reaching Earth's surface is longer-wavelength UVA, the rays standard glass lets through are exactly the ones you most need to plan around indoors and in the car.
Frequently asked questions
Does UV come through windows and clouds?
Largely, yes. Standard glass blocks most UVB but lets UVA through, so windows at home, in the office, or a car's side windows still expose skin to aging rays (laminated windshields block most UVA). Clouds stop only a fraction of UV, so protect skin near windows and on overcast days.
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/AsianBeauty: 'Why do K-beauty sunscreens talk about UVA so much more than US ones?'
Sources & citations
- Dermatology Times, 'Visible Light Protection: Needs and Strategies for Diverse Patients' (2023)
- dermatologytimes.com ↗