Does UV Get Through Windows? UVA, UVB, and Driving
Standard window glass blocks UVB but lets ~60% of UVA through — meaningful for drivers, office workers, and indoor sun exposure.
If you spend hours by a window or in a car, you may be getting more UV than you think. Standard glass blocks nearly all UVB — the burning wavelengths — but transmits a substantial fraction of UVA, which drives photoaging and contributes to skin cancer.
The numbers
Plain annealed window glass blocks ~97% of UVB but only ~37% of UVA (Almutawa et al., Photodermatol Photoimmunol Photomed 2013). Laminated windshields block almost all UVA. Side and rear car windows usually do not.
Clear annealed glass: 50–75%
Tempered side car window: 60–80%
Laminated windshield: 1–5%
Low-E coated glass: 5–25%
Why drivers see asymmetric aging
Dermatology journals have published striking case reports of unilateral photoaging on the driver-side face — wrinkling, lentigines, and even non-melanoma skin cancers concentrated on one cheek (Gordon & Brieva, NEJM 2012). The pattern matches decades of side-window UVA exposure.
Practical protection
Daily broad-spectrum SPF 30+ on face, neck, and hands covers most indoor and driving exposure. UV-protective window film (UPF 50+ films block 99%+ UVA) is a low-effort upgrade for cars and home offices.
Key takeaways
Glass blocks UVB but lets through significant UVA.
What to do with this Does UV Get Through Windows? UVA, UVB, and Driving data
Sunscreen labels are tested at 2 mg/cm². Typical real-world application is closer to half that, so DermUV assumes about half the labelled SPF when it estimates protected time.
The UV index is a measure of erythemal (skin-reddening) irradiance, where each whole point equals 25 mW/m² of UV energy reaching the surface. That is why burn-time estimates fall roughly by half when the index doubles.
Cumulative dose drives photoaging and long-term skin damage more than any single day. Small daily exposures on commutes, walks, and driving add up across a season.
Reapplication matters more than the SPF number. Reapply roughly every two hours outdoors and immediately after swimming, heavy sweating, or towelling, regardless of what the bottle claims.
Cloud cover is not protection. Thin or broken cloud can still pass most incoming UV, and light cloud edges can briefly scatter more UV toward the ground than a clear sky.
UV scale reference
The WHO scale groups UV 1-2 as low, 3-5 as moderate, 6-7 as high, 8-10 as very high, and 11 or above as extreme. Protection is recommended from UV 3 upward, and shade during the middle of the day becomes the priority from UV 8 upward.
A practical routine at moderate-to-high UV is roughly one ounce of broad-spectrum sunscreen for full-body coverage, applied 15 minutes before going out, then reapplied on schedule. Clothing, hats, and shade carry the rest of the load, especially for children and anyone with a history of easy burning.
Keep exploring DermUV
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