How does the sun burn skin?

    While you bake in your lounge chair, ultraviolet light from the sun zaps through your skin and kills living cells that normally work to help make new skin. Ultraviolet A, UVA, can travel more deeply into the skin, but both UVA and UVB rays can burn skin.

    Why does sunburned skin turn red?

    To repair the damage and remove the dead cells, blood vessels expand and blood flow increases to the burned parts of your body. The extra blood turns your skin red and warm.

    What causes sun-kissed skin to burn and itch?

    Damaged cells send messages to your brain, signaling they're injured and activating pain receptors, which makes your skin sensitive to touch

    Why does skin tan?

    In response to the UV rays frying your inner layer of skin, your body produces more melanin pigment that darkens the skin. The pigment absorbs the radiation and protects cells from damage. Most people don't tan after just one day at the beach, or one session in the tanning bed, because it takes time to make melanin.

    Why don't redheads tan?

    Melanin helps the body filter out UV radiation, but it also can be harmful. Pheomelanin, the type of melanin that makes red and blonde hair and fair skin, actually increases the risk for sun damage, such as sunburn and skin cancer.

    How does sunscreen work?

    The most effective sunscreens protect against both UVA and UVB rays. They work by either chemically absorbing UV rays or deflecting and bouncing them off your body.

    Is SPF 30 twice as good as SPF 15?

    Not quite. SPF tells you how long you have before you burn. Wearing SPF 2 lets you stay in the sun twice as long as without. An SPF 30 gives you 30 times your natural protection, and deflects 97 percent of the sun's burning rays, whereas SPF 15 deflects 93 percent.

    Why are we more likely to get sunburns on the beach?

    The sun's rays can reflect off of sand and water （snow, too）. And there are other factors: UV is strongest in the summertime, at midday, at higher altitudes, and close to the equator. Even on a gray day, up to 80 percent of the sun's rays can pass through clouds, mist, and fog.

    A little redness never hurt anyone, right?

    Wrong. Exposure to UV rays can mutate your cells and cause cancer. Blistering sunburns during childhood and adolescence increases your risk of developing skin cancer as an adult, because melanoma has more time to develop over your lifetime. Other nasty effects: wrinkled and leathery skin, brown sunspots, and cataracts.

    What's the best way to treat a burn?

    It may take a day before you see the full rosy damage. Pop aspirin immediately?it may lessen early development of sunburn. Drink water. Treat first- and second-degree burns with cool baths, moisturizers such as aloe vera and hydrocortisone creams. See your doctor if burns accompany headache, chills, or fever.

    1.为什么太阳会晒伤皮肤？

    当你在躺椅里晒太阳的时候，阳光中的紫外线穿透你的皮肤，杀伤正常状态下帮助你皮肤更新的活细胞。紫外线A,也就是长波紫外线，穿透皮肤更深，不过紫外线A和B都能晒伤皮肤。

    2.为什么太阳晒过的皮肤会变红？

    为了修复损伤并清除死细胞，你的身体晒伤部位的血管会扩张、血流量会增大。这种多于平常的血量让你的皮肤发红发热。

    3.为什么被晒伤的皮肤有灼痛感并且发痒？

    受损细胞向你的大脑发出信息，传递受伤的信号并激活疼痛受体，使得你的皮肤对触碰变得敏感。

    4.为什么会晒黑？

    作为对紫外线灼伤内皮层的反应，你的身体会产生更多的黑色素使皮肤颜色变深。黑色素可以吸收辐射，保护你的细胞不受损伤。不过大多数人只在沙滩上玩一天或者使用晒黑床一个周期不会晒成古铜色的皮肤，因为黑色素的合成是需要时间的。

    5.为什么红头发的人不适合晒黑？（外国人以古铜色皮肤为美，这是指那些故意的人说的吧……）

    黑色素可以帮助身体过滤紫外线，但它也有害处。红发或者金发、白色皮肤的人体内含有一种特殊的黑色素--褐黑素，它会增加被阳光损伤的风险，比如晒伤和皮肤癌。

    6.防晒霜是怎样起作用的？

    最有效的防晒霜既能防护紫外线A也能防护紫外线B.它们的工作原理要么是含有能吸收紫外线的化学物质，要么是使紫外线折射或色散，避开你的身体。

    7.防晒指数（SPF）30的防晒霜效果比防晒指数15的好两倍吗？

    其实并不是这样的。防晒因子代表你能在阳光下活动多久而不被晒伤。涂上防晒因子为2的防晒霜能让你在太阳下安全的呆上什么都不涂的2倍时间。防晒因子30能让你比只依赖你的天然防护系统多呆30倍的时间，也就是阻挡97%的紫外线，而防晒因子15则能阻挡93%.

    8.为什么在海滩上更容易晒伤？

    因为沙子和海水可以反射太阳光（雪也可以）.当然还有其他原因：在夏天、正午、高海拔和靠近赤道的地方，紫外线特别强烈。甚至当天看起来灰蒙蒙的时候，还是有80%的太阳光可以透过云层、薄雾和浓雾照下来。

    9.稍微晒红一点不碍事的，对吗？

    不对。暴露在紫外光下会使你的细胞突变，引起癌症。童年或者青少年时的晒伤会是你成年后患皮肤癌的风险增加，因为在你的一生中黑色素的合成时间增多了。其他令人讨厌的结果还有皮肤起皱纹、变粗糙、长褐斑，还有白内障。

    10.怎样正确处理晒伤？

    皮肤发红可能要晒后一整天才能完全表现出来。立即吃阿司匹林，它可以帮助你在晒伤早期减轻它的发展。多喝水。对于一级和二级晒伤，用凉水冲洗，再抹上点保水的东西，比如芦荟胶或者氢化可的松乳膏。如果你的晒伤还伴有头痛、寒战或者发烧症状，就赶快去看医生。