Getting a suntan through glass is a common question with a nuanced answer. While glass offers some protection from the sun’s rays, it does not provide complete immunity, meaning certain effects of sun exposure, including tanning, can still occur. Understanding how different types of ultraviolet (UV) radiation interact with glass clarifies this issue.
The Sun’s Rays and Your Skin
Sunlight contains ultraviolet (UV) radiation, primarily categorized into UVA and UVB rays that affect your skin differently. UVA rays have longer wavelengths and penetrate deeper into the skin, reaching layers beneath the surface. These rays are largely responsible for tanning, premature skin aging, and contribute to the development of skin cancer. Conversely, UVB rays have shorter wavelengths and higher energy levels, primarily affecting the skin’s outermost layers. UVB is the main cause of sunburn and plays a significant role in direct DNA damage within skin cells, which can lead to most skin cancers.
How Glass Filters UV Radiation
Standard window glass, found in homes and most vehicle side windows, offers partial protection against UV radiation. It effectively blocks nearly all UVB rays, which explains why you are unlikely to get a sunburn while indoors or in a car. This blocking action means that vitamin D synthesis, which primarily requires UVB exposure, cannot occur through typical glass.
However, common glass allows a substantial portion of UVA rays to pass through. About 37% to 75% of UVA can penetrate ordinary glass, leading to potential tanning and long-term skin effects. Car windshields offer better protection, typically made of laminated glass that blocks 80% to 98% of UVA and nearly all UVB.
Beyond Tanning: Other Effects of Sun Exposure Through Glass
Even without visible sunburn, chronic exposure to UVA radiation through glass can have significant health implications. UVA rays penetrate deeply into the skin, contributing to accelerated skin aging (photoaging), manifesting as wrinkles, sunspots, and a loss of skin elasticity. UVA damage is cumulative, adding up over years. This continuous exposure through windows, even at lower intensities, increases the risk of certain skin cancers, including melanoma and squamous cell carcinoma. Studies have observed individuals, such as truck drivers, developing more significant sun damage on the side of their face consistently exposed to sunlight through a vehicle window.
Protecting Yourself Indoors and In Vehicles
To minimize UV exposure when spending extended periods near windows, several protective measures can be taken. Applying broad-spectrum sunscreen with an SPF of 30 or higher, which protects against both UVA and UVB rays, is practical, especially if in direct sunlight indoors or in a vehicle. Consider installing UV-protective window films on home and car windows; these films block over 99% of both UVA and UVB rays. For vehicles, while windshields offer good protection, side and rear windows often do not, making window film a beneficial addition. Positioning furniture away from direct sunlight or utilizing blinds and curtains can further reduce indoor exposure.