HEAT AND SOLAR INJURIES - Medicine for Mountaineering and Other Wilderness Activities - page 420

Ultraviolet exposure at high altitudes is greater than at sea level because the atmosphere
is thinner and filters out less sunlight, particularly in the harmful wavelengths. The rate of
increase is 4 percent/1000 feet (300 m). Snowfields and glaciers reflect about 75 percent
of the incident ultraviolet radiation; in a cirque or bowl, reflection can increase the radi-
ation even more. Individuals participating in water sports are exposed to direct radiation
and large quantities (up to 100 percent) of reflected radiation. High-altitude sailboarding
can result in major ultraviolet exposures.
Sensitivity to Sunlight
Individuals vary widely in their sensitivity to sunlight. Redheads are particularly sensit-
ive.Blueeyedblondesaremoresusceptibletosunburnthanbrunettes.Individualsofnorth-
ern European ancestry are more sensitive than Mediterranean, Indian, African, or other
peoplewhoseskincontainsmoreprotectivepigment(melanin).Childrenaremoresuscept-
ible than adults.
Sensitivity to sunlight may be increased by a wide variety of drugs, such as sulfon-
amides and their derivatives (trimethoprim-sulfamethoxazole—brand names Bactrim and
Septra®); oral antidiabetic agents; thiazide diuretics suchashydrochlorothiazide; most tet-
racyclines, particularly doxycycline, which may be used for malaria prophylaxis; and the
fluoroquinolones such as ciprofloxacin (Cipro®). Many other substances such as biothion-
ol, which is used in soaps; many first-aid creams and cosmetics; green soap; many plants
and grasses such as fig leaf, certain meadow grasses, wild parsnip, celery, and others; dyes
used in lipstick; and coal tar or coal tar derivatives increase sensitivity to sunlight.
UVA and UVB
UVA makes up 95 percent of all solar ultraviolet radiation and varies less with altitude
andtime ofdaythan UVB.UVAincreases pigmentation andthickness ofthe outer layer of
the skin, producing a suntan that is protective because the pigment and the thickened skin
reduce the penetration of ultraviolet radiation. UVA penetrates the skin more deeply than
UVBandpotentiatesthechangesproducedbyUVB.UVAdamagestheelasticfibersinthe
skin and is primarily responsible for such aging changes as wrinkling.
UVB,althoughitmakesuponly5percentofallsolarultravioletradiationandpenetrates
less deeply than UVA, is the major cause of sunburn and skin cancer. This type of ultravi-
olet radiation damages the DNA in skin cells, which ultimately leads to malignancy.
Sunburn
Mildly excessive exposure to UVB produces redness (due to dilatation of cutaneous
blood vessels) and slight swelling and induration. Greater exposure causes pain and blis-
tering. Severe burns may be associated with chills, fever, or headache. Sunburn of the lips
is often followed by painful Herpes simplex infections (fever blisters or cold sores).