While many people refer to ultraviolet radiation as "UV light," this term technically is incorrect because you cannot see UV rays. Ultraviolet radiation is invisible.
There are three categories of UV radiation:
These are the highest energy UV rays and potentially could be the most harmful to your eyes and skin. Fortunately, the atmosphere's ozone layer blocks virtually all UVC rays.
But this also means depletion of the ozone layer potentially could allow high-energy UVC rays to reach the Earth's surface and cause serious UV-related health problems.
UVC rays have wavelengths that range from 100 to 280 nanometers (nm).
UVB rays have slightly longer wavelengths (280-315 nm) and lower energy than UVC rays. These rays are filtered partially by the ozone layer, but some still reach the Earth's surface.
In low doses, UVB radiation stimulates the production of melanin (a skin pigment), causing the skin to darken, creating a suntan.
But in higher doses, UVB rays cause sunburn that increases the risk of skin cancer. UVB rays also cause skin discolorations, wrinkles and other signs of premature aging of the skin.
Overexposure to the sun's UVB radiation also is associated with a number of eye problems, including pinguecula, pterygium and photokeratitis ("snow blindness").
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Because the cornea appears to absorb 100 percent of UVB rays, this type of UV radiation is unlikely to cause cataracts and macular degeneration, which instead is linked to UVA exposure (see below).
UVA rays are closer to visible light rays and have lower energy than UVB and UVC rays. But UVA rays can pass through the cornea and reach the lens and retina inside the eye.
Overexposure to UVA radiation has been linked to the development of certain types of cataracts, and research suggests UVA rays may play a role in development of macular degeneration.
