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. 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.

我们习惯于把头发仅仅当作个人风格的一种反映，但是作为我们身体的一个不断生长的部分，头发与我们的生理系统息息相关。美国皮肤学会教员、皮肤科医学博士马诺莫尼表示：“头发可以反映出身体内部的变化——比如疾病、营养和压力。” 我们的头发包含三个部分：毛干(纤维)，毛球(根部)和毛发周期(休息和再生的周期)。马诺莫尼表示，大多数的头发问题都与其中的某个部分相关。

1. Issue: Excessive hair shedding 脱发严重

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 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.

每根头发都有它自己的生长周期，生长6-8年后，停止生长几个月，然后脱落。马诺莫尼说：“百分之十左右的头发会在任何一个特定的时间脱落。”她指出，压力、发烧、体重减轻或缺铁等因素都会打断头发的生长周期，并使更多的头发提早脱落。如果你发现头发脱落比平时更多，检查一下自己的生活方式，看看发生了什么改变或者咨询一下皮肤科医生。

2. Issue: Hair that is dry and has lost its luster 头发干燥并失去光泽

"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, 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.

马诺莫尼医生说：“当头发角质层开始破坏，内部纤维暴露的时候，头发就会变得干燥。”过度加热将导致这种情况发生，尤其是对湿发加热。她建议在用电吹风吹干头发之前，先采用自然风干，并且使用日常护发素。请记住，毛纤维的颜色更容易损坏，所以染发的时候要格外小心。

3. Issue: Brittle or easily breaking hair 头发变脆容易断裂

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.

马诺莫尼医生指出，有些发型实际上会影响到你发球的健康。她看到许多人日复一日地拉伸头发或者把马尾绑得太紧。她说：“想想看，如果你一直拉植物的根部，那么植物最终将被损坏。”向后拉头发的时候手要放松，头发湿的时候不要用力地梳头发，使用宽齿梳子轻轻地梳。效仿玛莎·布雷迪为了头发亮泽，一天梳头100次？马诺莫尼医生说这样是不对的。梳得越少越好。

4. Issue: Split ends 头发末梢分叉

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.

分叉或死亡的头发末梢是头发受损或风干造成的。马诺莫尼医生说：“头发分叉是因为毛干的表层(或角质层)已经损坏。”但是好的一面是，你可以立即剪掉它，然后你的头发立刻看起来更加健康。另一个窍门是妥善调理你的发梢。记住清洗和调理的功能是不同的：洗发水是针对你的头皮，而护法素实际是针对头发纤维。

5. Issue: Gray hair 白发

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.

你应该坚信，除了染色外，白发是遗传的，这是不可避免的事实。大多数人的头发周期不长(记住，一个周期是6 -8年)，此时色素细胞包围毛囊，色素的产生处于最佳状态。然后过程变得......疲劳。马诺莫尼医生不能确认老妇人讲的如果你拔一根白发，五根将会长出来的传言。然而，一旦头发纤维变白，即使你拔掉头发，长出来的很可能还是白头发。

6. Issue: Dandruff 头皮屑

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.

头皮屑可以遗传，但什么原因导致了片状东西的产生还是一个谜。每天洗头是你的第一道防线，但是如果发痒且头屑一直存在的话，就去试试去屑的产品。但是，马诺莫尼告诫大家要谨慎地使用这些产品，因为它们对你的头发纤维刺激性很大。用去屑产品替代常规洗发水，一旦头皮屑清除，就换回常规洗发水。

7. Issue: An unexpected bald patch of hair 意想不到的秃顶

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. If you find a sudden bald spot, see your dermatologist.

当免疫系统开始攻击毛球，你可能出现秃发现象。免疫系统并没有摧毁它，但是毛球在攻击停止之前不会再生长了。根据全国秃发基金会的数据显示，秃发影响到在美国的500万人。马诺莫尼医生说：“至今我们不知道确切的原因，这可能是压力或者环境因素造成的。”秃发可能发生一次也可能以一定的频率发生。头发还能变黑因为这不是永久性的损坏。如果发现突然性的秃发，请去找皮肤科医生。

8. Issue: Thicker hair than you've ever had before. 头发比以前更密

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, your hair stays in a high state of hair growth, with only minimal hair loss. Enjoy it while it lasts!

要么你只是超级幸运，或者你即将有一个孩子。当然，孕激素使你对午餐失去胃口，但是你可能注意到它们也是你头发变得浓密有光泽的原因。当你怀孕后，你的头发会保持高增长的状态，只有很少的头发会脱落。享受这段头发持续高增长的时光吧！