Can You Tan Through a Window?

The skin is the largest organ of the human body; it has many functions, including thermal insulation and protection from external aggression. It therefore protects us in part from the harmful effects of the sun's UV rays.

As a reminder, these rays are classified into three categories according to their wavelengths: UVA (400-315 nm), UVB (315-280 nm) and UVC (280-100 nm). UV-C is the most harmful, but fortunately, it is filtered by the ozone layer and does not reach the surface of the Earth. On the other hand, UVA and UVB come into contact with the epidermis. When exposed to the sun, to protect the skin, melanocytes produce melanin (the pigment that gives the skin its brown color) which migrates to the surface of the epidermis and colors it: this is called tanning. If the exposure is too long or the UVB rays are too intense, the tan gives way to a sunburn. 

UVB rays are particularly aggressive for the skin and are responsible for sunburn. UVA rays penetrate further than UVB rays and reach the dermis, the deep layer of the skin. They are the cause of “photoaging”.

And, do windows block UV rays? According to a recent study conducted by American researchers, typical home, office, and car windows block most UVB rays, the ones responsible for tanning and sunburn. Tanning through the window is still possible but greatly limited. Similarly, getting sunburned behind glass is still possible even if the risks are minimal.

Beware, windows have the ability to block a large part of UVB rays, but they absorb the passage of UVA rays less well. Penetrating then until the dermis, these radiations accelerate the cutaneous aging. A study illustrates this case perfectly. It shows a photo of a 69-year-old milk deliveryman who spent 28 years behind the wheel. The left side of his face has aged at an accelerated rate under the effects of the sun (photoaging) while his right side appears much less marked.

So, if you spend a lot of time behind the glass, do not rely on windows blocking UV, but be sure to apply a broad-spectrum sunscreen that is appropriate for your skin type. Moreover, you should use a moisturizer that meets your skin's needs to fight dehydration, wrinkles and protect it from external aggressors.