Can Sunlight Through Your Car Window Still Damage Your Skin?

Sunscreen gets applied before stepping outside. That is the mental model most people operate on, and it misses a significant source of daily UV exposure entirely. UVA radiation, the longer-wavelength band that reaches deeper into the dermis and drives photoageing, is not meaningfully blocked by standard float glass, which is the type used in most car windows, office facades, and home windows.

Standard float glass blocks most UVB radiation, the shorter-wavelength band responsible for sunburn. This is why you cannot get a sunburn sitting by a window. It does not block UVA in any useful proportion. Uncoated float glass transmits roughly 75 percent of UVA, and the figure varies only modestly by glass thickness. Laminated glass, used in car windshields in most markets, including India, because it holds together on impact, performs better, blocking a larger portion of UVA. Side and rear windows in most cars are tempered glass, not laminated, and they transmit UVA at levels close to standard float glass unless they carry a UV-filtering film. The practical result: the driver's left side and the passenger facing a glass office wall are receiving meaningful UVA exposure across a working day.

UVA penetrates to the dermis, the layer where collagen and elastin fibres are produced and maintained. It generates reactive oxygen species that damage fibroblasts, the cells responsible for collagen synthesis, and it directly degrades existing collagen through matrix metalloproteinase activation. It also drives pigmentation by oxidising melanin already present in the skin and by stimulating melanocytes to produce more. This is distinct from UVB-driven pigmentation, which takes hours to appear after a burn. UVA-driven pigmentation can develop faster and tends to be more diffuse. For people managing melasma, post-inflammatory hyperpigmentation, or uneven skin tone, cumulative UVA exposure through glass is a relevant and often overlooked variable.

The exposure accumulates asymmetrically. People who drive regularly often show more photoageing on the left side of the face and the left forearm than the right, a pattern documented in dermatological literature on drivers in left-hand-traffic countries, and reversed in right-hand-traffic countries like India. Office workers seated near east- or west-facing windows receive a meaningful daily dose across a standard working week. This is not equivalent to unprotected midday sun exposure, but it is not negligible either, particularly across years. People with Fitzpatrick skin types I through III, those managing active pigmentation conditions, and those on photosensitising medications, certain antibiotics, retinoids, and antifungals, have more reason to account for this exposure than others. If you are on a photosensitising medication, discuss sun-protection strategy with the prescribing doctor, including indoor exposure.

Broad-spectrum sunscreens rated for both UVA and UVB protection are the most practical intervention. In India, the Bureau of Indian Standards and international standards used by most sunscreen brands rate UVA protection separately from SPF, which measures only UVB protection. Look for a PA+++ or PA++++ rating, or a UVA circle logo on European-standard products, alongside the SPF number. Applying sunscreen only on days with outdoor plans leaves the daily commute and the desk-by-window unaddressed. For people who want a structural solution rather than daily sunscreen application at a desk, UV-filtering window film applied to car side windows and office glass reduces UVA transmission substantially, some films bring transmission below ten percent. This is a one-time intervention that changes the baseline rather than requiring a daily behaviour change. It does not replace sunscreen for outdoor exposure. Protective clothing, a long-sleeved layer over the left arm while driving, for instance, is a low-cost option that requires no product at all. The right choice depends on skin sensitivity, the nature of the commute, and what someone will actually do consistently. A dermatologist can help assess whether your current routine accounts for your real daily exposure pattern, particularly if you are managing pigmentation or photoageing concerns that are not responding as expected.


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