Ultraviolet light comes from the sun's rays but is invisible to humans. Two of the three forms of ultraviolet light, UVA and UVB rays, reach the earth and can damage a person's skin and eyes.
UVA and UVB rays are reaching the earth at greater intensities because of the thinning of the ozone layer.
UVA rays are most intense in the morning and afternoon. These rays go right through window glass and can penetrate deeply into the skin. These rays can cause temporary and permanent skin changes.
UVB rays are most intense around the middle of the day when the sun is brightest, between about 10 a.m. and 4 p.m. in most areas. Window glass blocks these rays. UVB rays affect the outer layer of the skin and can cause sunburns.
A person may look tan soon after being exposed to UVA and UVB rays. Long-term effects of exposure include premature aging, wrinkling, skin damage, and sometimes skin cancer.
Tanning booths also use and transmit ultraviolet light.