UVA Through Glass: What Windows Do and Do Not Block
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In 2012 the New England Journal of Medicine published a photograph of a 69-year-old man who had driven a delivery truck for 28 years. The left side of his face, the side by the window, was visibly more aged than the right: thickened, deeply lined, with pronounced loss of elasticity. The case was titled unilateral dermatoheliosis.1
It is one photograph of one person, and a single case cannot tell you how much of that was the window. It is memorable because the comparison is built into the same face.
What glass does and does not stop
Ordinary window glass blocks most UVB, the shorter wavelength largely responsible for sunburn. It transmits a substantial proportion of UVA, the longer wavelength associated with photoaging. That is why you do not burn through a window but the exposure is not zero.
Edlich and colleagues reviewed the use of UV-protective windows and window films as a skin cancer prevention measure, which is the practical response to the same physics.2
Vehicle windscreens are usually laminated and block more UVA than side windows, which are typically tempered. That difference is the reason the effect in the case above was one-sided.
Does this mean sunscreen indoors?
Honestly, it depends on where you sit. If you commute a long way, drive for work, or spend your day beside a sunny window, the exposure adds up in a way it does not for someone in an interior office.
What we would not say is that everybody needs sunscreen to sit indoors. Sensible steps:
- If you drive a lot, treat it as sun exposure. A daily broad-spectrum sunscreen covers it without a decision each morning.
- Look at where you actually sit. A desk beside north-facing glass in Auckland is not the same as one in the middle of a room.
- Broad spectrum is the phrase that matters. Blocking UVB alone does not address the wavelength that gets through glass.
Ask us
If you want a sunscreen you will genuinely wear every day, that is a fitting question rather than a product question. Come in and we will find one that suits your skin.
References
Each PMID resolves on Europe PMC, so you can read the paper rather than take our word for it.
- Gordon JR. Images in clinical medicine. Unilateral dermatoheliosis. New England Journal of Medicine, 2012. PMID 22512500
- Edlich RF. Use of UV-protective windows and window films to aid in the prevention of skin cancer. Journal of Long-Term Effects of Medical Implants, 2004. PMID 15479155
