American Melanoma Institute · 5 min read
Which kinds of UV pass through car, office, and airplane windows, what screens and nail lamps emit, and how small daily exposures add up.
Most lifetime sun exposure comes in small, forgettable pieces: the commute, the desk by the window, the walk to lunch. Glass changes that exposure in a way that is easy to miss, because it stops the rays that burn and lets through many of the rays that don't.
Sunlight carries 2 kinds of ultraviolet light that reach the ground. UVB has more energy and mainly affects the outer layer of skin. It causes most sunburns. UVA has less energy per ray and reaches the dermis, the thicker layer under the surface, where it drives tanning, wrinkling, and other signs of skin aging. Both kinds damage DNA and both contribute to skin cancer. A third kind, UVC, is absorbed by the ozone layer.
UVA is present all day and all year, and it passes through clouds. Ordinary window glass filters out most UVB. According to the Skin Cancer Foundation, more than 50% of UVA can pass through it. Behind a window you are unlikely to burn, so the usual warning sign never arrives, while UVA exposure continues.
A car has 2 kinds of glass. The windshield is laminated: 2 sheets of glass bonded to a plastic layer that keeps it from shattering, and that layer also absorbs UVA. Side windows, rear windows, and most sunroofs are tempered glass with no such layer.
An ophthalmologist measured the difference in 29 cars from 15 manufacturers (Boxer Wachler, JAMA Ophthalmology, 2016). Windshields blocked an average of 96% of UVA, and every one tested fell between 95% and 98%. Driver's side windows averaged 71%, with a range from 44% to 96%. Only 4 of the 29 cars had side windows that blocked more than 90%.
Dermatologists in countries where the driver sits on the left have long noticed more sun damage on the left side of the face and the left arm. A review of patients treated at the Saint Louis University Mohs surgery unit in 2004 (Butler and Fosko, Journal of the American Academy of Dermatology, 2010) found 52.6% of skin cancers on the left side of the body. The difference was stronger in men. For melanoma in situ, the earliest stage of melanoma, 31 of 42 cases (74%) were on the left.
A study from one referral center cannot prove that driving caused the difference, and more data is needed. The pattern does fit what the glass measurements predict.
Clear or tinted UV window film can be added to side windows, sunroofs, and the windows of a house or office. Films that carry the Skin Cancer Foundation's Seal of Recommendation must block 99% or more of UVA and UVB, and the foundation notes that a film can last up to a decade. States set their own limits on how dark car window tint may be, so check local rules before installing it.
A desk or favorite chair right beside a large sunny window delivers UVA for hours a day. Film, blinds, or moving the chair a few feet all reduce it.
UV gets stronger with altitude because there is less atmosphere above to filter it. A meta-analysis of 19 studies with more than 266,000 participants (Sanlorenzo and colleagues, JAMA Dermatology, 2015) found that pilots and cabin crew develop melanoma at about twice the rate of the general population.
The same group measured UV inside the cockpit of a small turboprop plane. The windshield blocked UVB at every altitude and let UVA through. By their calculation, about 57 minutes of flying at 30,000 feet delivered the same UVA dose as a 20-minute tanning bed session. Windshields on large airliners may perform differently, and flight crews are also exposed to cosmic radiation, so the cause of the higher melanoma rate is not settled.
Much less is known about passengers. Lowering the window shade on a long daytime flight removes the question.
Phones, tablets, computer monitors, and televisions do not give off meaningful UV. A Brazilian dermatology group measured UVA and UVB from household lamps, TVs, tablets, and computers and detected no emission that would pose a risk (Duarte and colleagues, Anais Brasileiros de Dermatologia, 2015). Standard LED bulbs fall in the same category.
The lamps that cure gel nail polish, including the ones sold as LED lamps, give off mostly UVA. A laboratory study found that repeated exposure to a nail dryer damaged DNA and left lasting mutations in human and mouse skin cells grown in dishes (Zhivagui and colleagues, Nature Communications, 2023). Cells in a dish are a long way from hands in a salon, and no large study has yet shown whether regular gel manicures raise skin cancer rates in people. More data is needed.
The exposure per session is short, and the precaution is easy. The American Academy of Dermatology suggests applying a broad-spectrum, water-resistant sunscreen with SPF 30 or higher to the hands before a gel manicure, or wearing dark, opaque gloves with the fingertips cut off.
UV damage is cumulative, and skin keeps no separate account for a beach day and a year of commutes.
For that reason, dermatologists recommend a broad-spectrum sunscreen with SPF 30 or higher on the face, neck, ears, and the backs of the hands every day you will be outdoors or on the road. The words "broad-spectrum" on the label mean the product has passed a test for UVA coverage, which is the part that counts behind glass. A long-sleeved shirt on a long drive protects the window-side arm better than any sunscreen.
