As we rev up for bikini season, it’s also time to start thinking about skin protection. UV radiation, specifically UVB radiation from the sun, is a known risk factor for the most common kinds of skin cancer: squamous cell carcinoma and, to a lesser extent, basal cell carcinoma. UVB is also what creates sunburns, suntans, and enables your skin to create the essential vitamin D.
While most of us know that sunscreen can help protect us from UVB-induced sunburn, some people claim that you cannot burn or tan through windows or glass. Is there any truth to this, and if so what exactly gets through the glass?
It turns out that there is some truth to the rumors, but that doesn’t mean we are completely out of the woods when we feel the sun through the windows. Scientists have known for a while that glass filters out most of the harmful UVB rays that cause sunburn by directly damaging DNA, but lets through UVA and visible light. UVA can still cause some tanning, but at a much reduced rate compared to UVB. With long enough exposure, it is possible to burn through glass as well.
The problem with UVA is that it is not as innocuous as was once believed. Though UVB radiation damages DNA directly, UVA damages DNA indirectly by increasing oxidation. Furthermore, malignant melanoma, the most deadly kind of skin cancer, is thought to be associated more with UVA than UVB exposure. Therefore, even in the absence of sunburn, sun exposure through glass (and sunscreen) may still increase melanoma risk compared to sun avoidance, though the data is controversial.
As you might suspect, the type of glass between you and the sun matters as well. While regular glass transmits 75% of UVA radiation, both laminated and green colored glass can block UVA completely (that’s also the reason good wines and olive oils are often found in green glass). Tinted car windows also reduce UV exposure.
To summarize, though you are unlikely to become sunburned through glass, some tanning and burning can occur with excessive exposure, and may also increase your risk of malignant melanoma. Both glass and sunscreen are likely to protect you from squamous and possibly basal cell carcinoma if burning does not occur often. Since UVB radiation from the sun is still the best source of vitamin D for humans, short-duration but frequent sun exposure that does not result in sunburn is the best practice based on our current knowledge.
When it comes to the science of wellness, distinguishing the facts from the urban legends can be tough. That’s why we’ve enlisted Darya Pino – a scientist, foodie, and self-proclaimed geek girl. Check out the ZocDoc Blog every other Tuesday to see her bust the biggest myths in health.
Image: Ryann Looking Through a Rose Quartz at the Desert, a Creative Commons Attribution (2.0) image from Claire L. Evan’s photostream.