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UVA light and skin

10 Jun

UVA rays are a type of light emitted from the sun. UVA rays are known to cause premature skin aging with wrinkles, elasticity loss, and age spots. They can also trigger hyperpigmentation (for example, post-acne marks and melasma). UVA rays are responsible for the natural tanning of our skin (this is why the so called "healthy tan" always comes together with skin damage). UVA rays contribute to development of skin cancers.

UVA rays are defined based on the length of their wave. UVA light has the wavelength between 320 and 400 nanometers. Not all UVA sunscreen filters can cover this range in full, and this is why it is useful to split the UVA spectrum further into the UVA I (the longest UVA waves with the length of 340 to 400 nanometers) and UVA II (shorter UVA waves with the length of 320 to 340 nanometers). Most of the UV radiation we are exposed to falls within the UVA I range (long rays). At the same time, protection against the UVA I rays (the longer ones) is the most tricky to achieve. Because of that, in skincare, a sunscreen filter is defined as a UVA one in most cases only if it is able to protect against the long UVA waves (UVA I).

In general, all UVA waves are shorter than the UVB ones. This is why they are able to penetrate human skin deeper than the UVB light. At the same time, UVA light has less energy in it, meaning that it does not cause a direct damage to the skin cell DNA in the same way that the UVB rays do. Unfortunately, it is still causing the DNA damage, but through an indirect mechanism (it creates free radicals that then can cause chemical reactions that are harmful to the skin health).

UVA light reaches the surface of Earth even when the weather is cloudy. It can also penetrate through glass in windows.

Some of the popular UVA / broad spectrum filters used in sunscreen include (all of the ones listed below protect from the long, UVA I rays; broad spectrum filters protect both from the UVA and UVB light):

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