Ultraviolet (UV) radiation forms part of the electromagnetic spectrum between visible light and X-rays; it is invisible to the human eye. UV light can be separated into three bands, UVA (400-320nm), UVB (320-290nm) and UVC (290-100nm). Of the UV radiation that reaches the Earth’s surface from the sun, approximately 6% is UVB and 94% UVA.
Skin maintains a curious balance with UV radiation. When UV impacts upon skin, the various wavelengths of light penetrate to different levels and thus have a number of effects.
The longer wavelength, UVA, penetrates deeply into the skin. Commonly known as the ‘aging’ ray, UVA breaks down collagen and indirectly contributes to the risk of skin cancer by causing the production of free radicals, which can damage DNA.
The shorter wavelength, UVB, is known to directly damage the DNA within skin cells, as well as causing sunburn. UVB also initiates the synthesis of vitamin D in the skin by exciting a precursor molecule. Finally, it is predominantly UVB wavelengths which are responsible for activating the protective melanin response (i.e. the ‘tanning response’) in the skin; this helps to reduce the impact of subsequent UV exposure. The figure below (click to enlarge) summarises the effects of UVA and UVB on skin.
This piece is adapted from Clinuvel’s latest Technology Update: Stem Cells and Repigmentation in Vitiligo.
You can read more about interactions between UV light and skin on our skin and health website.
Top image reference
“Light after Darkness” posted to Flickr.com by JD | Photography on October 23, 2008 <http://www.flickr.com/photos/japokskee/4440609236/>