We tend to regard hair only as a reflection of our personal style, but as a living, growing part of our body, it's also tied in to our physiology. "Hair reflects internal changes -- things like sickness, nutrition and stress," says dermatologist Paradi Mirmirani, M.D., a faculty member of the American Academy of Dermatology and staff dermatologist with Kaiser Permanente. There are three parts to your hair: the hair shaft (the fiber), the hair bulb (the root) and the hair cycle (the period of rest and regeneration). Most problems are related to one of these three things, says Mirmirani.

Issue: Excessive hair shedding

Each individual strand of hair has its own cycle, growing for six to eight years, resting for a few months, and then shedding. "About 10 percent of your hair is shedding at any one given time," Mirmirani says, pointing out that many things can interrupt the cycle and cause more hairs to shed earlier, including stress, fever, weight loss (even 10 pounds) or low iron levels. If you're noticing more shedding than usual, examine your lifestyle to see what might have changed or consult your dermatologist for tests.

Issue: Hair that is dry and has lost its luster

Oh, the things we do to our hair in the name of beauty, like daily blow-drying and using the flat iron. "Hair becomes dry when the cuticle starts to break down and the inner fiber is exposed," Dr. Mirmirani says. Excessive heat can cause this -- especially heat applied to wet hair. She recommends air-drying your hair partially before blow drying, only using the flat iron on dry hair, and using a daily conditioner. Remember that hair fiber with color is more prone to damage, so be extra cautious if you color-treat your hair.

Issue: Brittle or easily breaking hair

Some hairstyles can actually affect the health of your hair's bulb, Dr. Mirmirani says. She sees this a lot with hair extensions or ponytails pulled too tight, day after day. "Think of it this way, if you keep pulling on the bulb of a plant, eventually, you can damage it," she says. Take it easy when you're pulling your hair back, and don't brush your hair vigorously when wet. Use a wide-tooth comb and comb through gently. As for Marsha Brady's 100 strokes a day for shine? Not so much, Mirmirani says. The less brushing, the better.

Issue: Split ends

Split, or "dead" ends are the result of damaged or weathered hair. "The hair splays apart because the outer layer (or cuticle) of the hair shaft has worn away," Dr. Mirmirani says. But the good news is, you can snip them right off, and immediately your hair will look healthier. Another trick is to keep your ends well-conditioned. Remember there is a difference between the function of cleansing and conditioning: Shampoo is for your scalp, and conditioner is for the actual hair fibers.

Issue: Gray hair

The unavoidable truth is that gray hair is genetic, and aside from coloring, you're stuck with it. Most people only have a handful of hair cycles (remember, a cycle is 6 - 8 years) where the pigment-producing cells that surround the follicle and transfer pigment are working at their best. The process just gets . . . tired. Dr. Mirmirani can't confirm the old wives' tales that tell you if you yank one gray hair, five more will sprout up. However, once a fiber is gray -- even if you pluck it -- it will more than likely grow back in gray again.

Issue: Dandruff

Dandruff can be hereditary, but it's still a mystery what causes the flaky stuff. Daily shampooing is your first line of defense, but if the itchiness and flakes persist, try an anti-dandruff product. Dr. Mirmirani cautions sparing use of these products, however, because they are very harsh to your hair fiber. Try alternating the anti-dandruff product with regular shampoo until the dandruff clears up, and then switch back to your regular shampoo.

Issue: An unexpected bald patch of hair

You may have Alopecia Areata, which occurs when your immune system starts attacking the hair bulbs. It doesn't destroy it, but the bulb won't start to grow again until the attack is called off. According to the National Alopecia Areata Foundation, it affects five million people in the U.S. "It could be stress or it could be environmental factors -- we really don't know," Dr. Mirmirani says. It can happen one time or recur with some frequency. The hair can grow back though -- it's not permanent damage. If you find a sudden bald spot, see your dermatologist.

Issue: Thicker hair than you've ever had before.

Either you're just super lucky, or you're about to have a baby. Sure, the hormones of pregnancy can make you lose your lunch, but they are also the cause behind the thick, lustrous hair you'll probably notice if you're expecting. When you're pregnant (and for a few months postpartum), your hair stays in a high state of hair growth, with only minimal hair loss. Enjoy it while it lasts!

我們往往僅僅把頭發當作個人風格的一種反映，但是作為我們身體的一個不斷生長的部分，它也和我們的生理系統有聯系。皮膚科醫生Mirmirani，醫學博士，美國皮膚學會教員和凱色永久皮膚科的工作人員說：“頭發內部反映了變化-像疾病，營養和壓力。”你的頭發包括了三部分：毛干(纖維)，毛球(根部)和毛發周期(休息和再生的周期)。Mirmirani說大多數問題都與這三部分的一部分有關系。

問題：過多的脫發

每一根頭發都有它自己的周期，生長6-8年，停止生長幾個月，然后脫落。Mirmirani說：“百分之十左右的頭發會在任何一個特定的時間脫落。”她指出，壓力，發燒，體重減輕(甚至10磅)或缺鐵等等將打斷頭發的周期，使更多頭發脫落的更早。如果您發現頭發脫落的比平時更多，檢查一下你的生活方式看看什么發生了改變或者咨詢您的皮膚科醫生并做些檢查。

問題：頭發干燥并失去光澤

哦，我們以美發名義做的事情，像每天的吹干燥和使用扁鐵。Mirmirani醫生說：“頭發變得干燥，角質層開始破壞和內部纖維暴露，”過度加熱將導致這種情況發生，特別是對濕發加熱。她建議在用電吹風吹干頭發之前，先采用自然風干，在干燥的頭發上僅僅使用扁鐵并且使用日常護發素。請記住，毛纖維的顏色更容易損壞，所以如果你染發的話要格外小心。

問題：頭發變脆容易斷裂

Mirmirani醫生說有些發型實際上會影響到你發球的健康。她看到了大量的這種情況，日復一日的拉伸頭發或者把馬尾辮拉的太緊。她說：“這樣想想看，如果你一直拉植物的根部，最終，你將破壞它。”當你向后拉頭發的時候放松，當頭發濕的時候不要用力地梳頭發，應使用寬齒梳子輕輕地梳。像瑪莎布雷迪為了光澤，一天梳個100次？Mirmirani醫生說并不是這樣。梳的越少越好。

問題：頭發末梢分叉

分叉或死的頭發末梢是頭發順壞或風干造成的。Mirmirani醫生說：“頭發分叉是因為毛干的表層(或角質層)已經損壞。”不過，好消息是，你可以立即剪掉它，馬上你的頭發看起來就更健康。另一個竅門是妥善調理你的發梢。記住清洗和調理的功能是不同的：洗發水是針對你的頭皮，而護法素實際是針對頭發纖維。

問題：白發

不可避免的事實是，除了染色外，白發是遺傳的，你應該堅持這種觀點。大多數人只有一小段頭發周期(請記住，一個周期是6 -8歲)，此時色素細胞包圍毛囊而且產生色素工作處于最佳狀態的。然后過程變得...疲勞。Mirmirani醫生不能確認老婦人講的如果你拔一根白發，五根將會生長出來的傳言。然而，一旦頭發纖維變白，即使你拔掉頭發，很可能再次長回白頭發。

問題：頭皮屑

頭皮屑是可遺傳的，但是是什么原因導致了片狀的東西產生還是一個謎。每天洗頭是你的第一道防線，但是如果癢而且片狀一直存在的話，試試去屑的產品。然而Mirmirani告誡大家保守地使用這些產品，因為他們對你的頭發纖維刺激很大。使用去屑產品代替常規洗發水知道頭皮屑被清除，然后換回常規洗發水。

問題：意想不到的禿頂

當你的免疫系統開始攻擊毛球，您可能已經禿發，免疫系統并沒有摧毀它，但是毛球在攻擊停止之前不會再生長了。根據全國禿發基金會，它影響到在美國的500萬人。Mirmirani醫生說：“這可能是壓力或者環境因素造成的--我們也不知道確切原因。”禿發可能發生一次也可能以一定的頻率發生。頭發還能變黑因為這不是永久性的損壞。如果您發現突然的禿發，去找您的皮膚科醫生看一下。

問題：頭發比以前更密

要么你只是超級幸運，或者你即將有一個孩子。當然，懷孕的激素可以使你對午餐失去胃口，但是如果你懷孕的話你可能注意到它們也是你頭發變密變光澤的背后原因。當你懷孕(好幾個月)，你的頭發保持高增長的狀態，只有很少的頭發會脫落。享受這持續高增長的時候吧！