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.為什么太陽會曬傷皮膚？

    當你在躺椅里曬太陽的時候，陽光中的紫外線穿透你的皮膚，殺傷正常狀態下幫助你皮膚更新的活細胞。紫外線A,也就是長波紫外線，穿透皮膚更深，不過紫外線A和B都能曬傷皮膚。

    2.為什么太陽曬過的皮膚會變紅？

    為了修復損傷并清除死細胞，你的身體曬傷部位的血管會擴張、血流量會增大。這種多于平常的血量讓你的皮膚發紅發熱。

    3.為什么被曬傷的皮膚有灼痛感并且發癢？

    受損細胞向你的大腦發出信息，傳遞受傷的信號并激活疼痛受體，使得你的皮膚對觸碰變得敏感。

    4.為什么會曬黑？

    作為對紫外線灼傷內皮層的反應，你的身體會產生更多的黑色素使皮膚顏色變深。黑色素可以吸收輻射，保護你的細胞不受損傷。不過大多數人只在沙灘上玩一天或者使用曬黑床一個周期不會曬成古銅色的皮膚，因為黑色素的合成是需要時間的。

    5.為什么紅頭發的人不適合曬黑？（外國人以古銅色皮膚為美，這是指那些故意的人說的吧……）

    黑色素可以幫助身體過濾紫外線，但它也有害處。紅發或者金發、白色皮膚的人體內含有一種特殊的黑色素--褐黑素，它會增加被陽光損傷的風險，比如曬傷和皮膚癌。

    6.防曬霜是怎樣起作用的？

    最有效的防曬霜既能防護紫外線A也能防護紫外線B.它們的工作原理要么是含有能吸收紫外線的化學物質，要么是使紫外線折射或色散，避開你的身體。

    7.防曬指數（SPF）30的防曬霜效果比防曬指數15的好兩倍嗎？

    其實并不是這樣的。防曬因子代表你能在陽光下活動多久而不被曬傷。涂上防曬因子為2的防曬霜能讓你在太陽下安全的呆上什么都不涂的2倍時間。防曬因子30能讓你比只依賴你的天然防護系統多呆30倍的時間，也就是阻擋97%的紫外線，而防曬因子15則能阻擋93%.

    8.為什么在海灘上更容易曬傷？

    因為沙子和海水可以反射太陽光（雪也可以）.當然還有其他原因：在夏天、正午、高海拔和靠近赤道的地方，紫外線特別強烈。甚至當天看起來灰蒙蒙的時候，還是有80%的太陽光可以透過云層、薄霧和濃霧照下來。

    9.稍微曬紅一點不礙事的，對嗎？

    不對。暴露在紫外光下會使你的細胞突變，引起癌癥。童年或者青少年時的曬傷會是你成年后患皮膚癌的風險增加，因為在你的一生中黑色素的合成時間增多了。其他令人討厭的結果還有皮膚起皺紋、變粗糙、長褐斑，還有白內障。

    10.怎樣正確處理曬傷？

    皮膚發紅可能要曬后一整天才能完全表現出來。立即吃阿司匹林，它可以幫助你在曬傷早期減輕它的發展。多喝水。對于一級和二級曬傷，用涼水沖洗，再抹上點保水的東西，比如蘆薈膠或者氫化可的松乳膏。如果你的曬傷還伴有頭痛、寒戰或者發燒癥狀，就趕快去看醫生。