Skin Types and Sun Exposure
Children in general are very sensitive to sunlight and have very thin skin that burns quickly but tans slowly. They should not be exposed to sunlight for more than 5-10 minutes. Infants (under 1 year) should not be exposed to intense sunlight at all.
Persons with very light skin, reddish hair and lots of freckles are most sensitive to sunlight. They may burn very quickly and tan very slowly. People with this type of complexion should avoid unprotected exposure to intense sunlight of longer than 20 minutes.
Light skin, in persons who are blond or strawberry blonde and often freckled also burns quickly and tans slowly. People with this complexion should avoid unprotected exposure to intense sunlight of longer than 20 to 30 minutes. Darker skin tones are more protective against sunlight but remember that even the darkest complexion doesn't make you immune to sunburn.
Protective clothing and a wide brimmed hat can protect when you are outside. Remember that UV rays are present even on cloudy days. Sunlight is strongly reflected from sand, snow, ice, and concrete and can increase your direct sunlight exposure up to 50%.
Wear sunglasses that filter out ultraviolet light to protect your eyes.
Be especially careful about sun exposure if you take medications like tetracycline, antihistamines, "sulfa" drugs, diuretics and some oral contraceptives. The combination of some drugs and sunlight can decrease the time needed to produce sunburn. (See below, Special Sunlight Sensitivities)
Types of Ultraviolet Radiation (UV)
Suntans are produced by two types of ultraviolet radiation in sunlight.
UVA rays constitute 90-95% of the sun's ultraviolet light reaching the earth and have a relatively long wavelength (320-400 nm) directly adjoining the violet end of the visible light spectrum. UVA light penetrates the furthest into the skin and is the primary inducer of tanning response in humans
UVB rays are partially absorbed by the ozone layer and have a medium wavelength (290-320 nm). They do not penetrate the skin as far as the UVA rays do but contain more energy and activate the synthesis of vitamin D and the absorption of calcium and other minerals. UVB rays are the primary cause of sunburn and of the most concern for skin and eye damage.