Here comes summer. Memorial Day begins the season of the sun for many Americans who take trips to the beach, play rounds of golf, swim and have all sorts of backyard activities. Summer also is tanning season. That is unfortunate, since the lighter-skinned among us are developing skin cancer at an increasing rate. There is no such thing as a healthy tan. True, tanned skin is less likely to burn, but tanned skin is damaged skin.
阳光含有强大的辐射。我们看到的光（可见光）温暖我们并为植物生长提供能量。这是我们没有看到的，导致伤害 - 太阳的紫外线（UV）光线。
There are three forms of UV — A, B and C. The earth’s atmosphere blocks the most damaging form: UVC. But the other two, UVB and UVA, reach beyond the clouds and ozone. UV light damages DNA and impairs the skin’s immune defenses. Damaged DNA can lead to skin cancer. If the skin’s damaged immune system fails to destroy the cancer, it grows and may spread.
UVB比UVA更深入地穿透，但即使是在晒黑展位的UVA，也与皮肤癌有关，包括黑素瘤，最危险的形式。环境保护局注意到五分之一的美国人将培养皮肤癌症。黑色素瘤发生率每年增加7％，是25至29岁的最常见的癌症。任何晒伤都会增加黑色素瘤的机会，特别是在儿童时期。
UVA and UVB also cause wrinkles and rough spots — noncancerous changes called photo aging — by damaging the supporting proteins in our skin. The price of today’s tan is premature aging of the skin. Many of the sun worshippers of 30 years ago are spending a small fortune on skin rejuvenation treatments and plastic surgery to look as young as the small number of their peers who never tanned or burned.
It’s not just light-skinned individuals who are at risk. Although darker skin is somewhat protective, it is a misunderstanding to think that getting a tan will protect the skin from the sun since damage occurs while getting the tan in the first place. Photo aging still occurs and skin cancer often is more advanced when diagnosed in darker-skinned individuals.
18岁的人们将获得一大部分终身阳光曝光。父母应该在保护他们的孩子免受阳光下保持警惕，但即使对于成年人而言，防晒是有益的。限制暴露于太阳的破坏性光线是最好的预防方法。
紫外线最强烈的10a.m. and 4 p.m. between April and October in northern latitudes. Don’t be comforted by clouds as most of the UV passes through them. Damaging UV exposure occurs even on cool days. Check the local paper orhttp://www.epa.gov/sunwise/uvindex.htmlfor the UV index for the day. The higher the number, the more protection will be needed.
Although UVA does contribute to the production of vitamin D, people need only 10 minutes of exposure three times a week to make enough. Plus people also obtain vitamin D from meat and fish and from supplements in milk and fortified cereals. So, everyone should use sun block.
Sun block is rated by sun protection factor, or SPF. The SPF says how many times longer one can stay in the sun before being burned compared to having no protection. Someone who burns after 30 minutes of unprotected exposure should be able to avoid a burn with an SPF 15 for 15 times 30 minutes or seven and a half hours. A sunscreen with SPF 15 blocks 93 percent of the damaging UV rays. The 7 percent that does pass can still cause skin aging and contribute to skin cancer. To maximize safety, one should use at least an SPF of 15 (SPF 45 blocks about 98 percent of UV) plus clothing and head covering when spending time outside.
For best protection, apply sun block to dry skin before going out to give it time to form a protective barrier. Moisture washes away even waterproof sun block so reapply it every two hours or so. Even then, try to stay in shade, for example, under an umbrella, and use a wide-brimmed hat for protection of the top of the head and ears. Remember to protect lips with sun-blocking lip balm.
Whether at the beach, a ballpark, a picnic or in the backyard, the object of sun protection is to reduce the risk of burning and cancer from the sun exposure that cannot be avoided. Since there is no safe tan, no one should intentionally stay in direct sunlight even with sun block. As the Centers for Disease Control says, “If you’re tanned, you’re toast.”
The best advice for outdoor activity is to cover the skin with clothing that does not let light through and wear sunblock on exposed surfaces. This is critical for children and highly recommended for adults. With a few precautions the summer sun can be enjoyed without burns, or increased risk of cancer, cataracts or the telltale signs of premature aging.
Original source: https://news.psu.edu/story/210024/2005/05/18/medical-minute-myth-healthy-tan