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。

­
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。