共用题干 Sunbath and Skin CancerIn the summer,millions of Americans will offer up their bodies to the su...

共用题干
Sunbath and Skin Cancer
In the summer,millions of Americans will offer up their bodies to the sun rays.A tan mndi-cates health and beauty,and most sun worshippers will sacrifice a lot to achieve it,including themselves.
With each hour, the sun's ultraviolet radiation (紫外线）produces irreversible（不可逆的） damage,hastening the development of unsightly wrinkles.And with each year on the beach or roof-top,the sunbather increases his risk of getting skin cancer. Skin cancer is by far the most common form of cancer. An estimated 400,000 new cases will be detected this year in the United States, and almost all of them can be blamed on over-exposure to the sun.
Fortunately,most of these cancers are highly curable .But they can he disfiguring and take time to treat. For that reason,sun worshippers should treat deity with a good deal of awe（敬畏）. Sunburn,of course,is the initial hazard posed by UV radiation.Prolonged exposure to UV,howev-er , interferes with the production of collagen fibers（胶原纤维）in the dermis（真皮层）, causing the skin to lose elasticity（弹性）and creating premature wrinkles. Further deterioration（恶化）of the dermis deprives the epidermis（表皮层）of nutrition and causes it to become thin and dry.
Cancer is UV's final result.Shortwave radiant energy,especially from the UV-B band,breaks the strands（股、缕）of DNA. Enzymes（酶）work constantly to rearrange the DNA into proper Se-quence,but with repeated UV exposure,the repair process may eventually break down.Then the mutant（变异的）DNA may produce a colony of cancer cells. But skin cancer may be avoided with a good dose of common sense.People with fair skin and blue eyes who burn easily stand the high-est risk .Special danger spots are the parts of the body most constantly exposed to the sun,such as the cheeks , nose , lower lip and the ears. People who have already developed precancerous（癌变前的）lesions（伤害）or had one skin-cancer growth stand a greatly increased chance of developing others.
Dermatologists（皮肤科医生）recommend avoiding the sun when it is most intense between 11 a.m.and 3 p.m.Anyone who insists on sunbathing should use a good sun screen.These lotions and salves（药膏）contain chemicals that block out the burning UVB radiation while permitting the tanning rays to reach the skin.