A human hair consists mainly of a protein called Keratin. It also contains some moisture and the trace metals and minerals found in the rest of the body.
人类的头发主要由一种叫角朊的蛋白质组成，并含有水分及在身体其他部分也可找到的微量金属和矿物质。
The only living part of hair is underneath the scalp--when the hair had grown through the scalp it is dead tissue.
头发唯一有生命的部分是在头皮下面，当它长出头皮时便成为无生命组织。
Hair’s natural shine is supplied by its own conditioner, sebum, an oil composed of waxes and fats and also containing a natural antiseptic that helps fight infection. Too much sebum results in greasy hair and conversely, too little sebum makes dry hair.
头发的自然光泽来自它自身的护发素：油脂，它含有蜡和脂肪，还含有抗感染的自然抗菌剂。油脂含量过多会导致油性发质，相反，油脂含量过少则会导致干性发质。
Hair grows about 12 mm per month. If a person never has his hair cut, it would grow to a length of about 107 cm before falling out. Hair grows faster in the summer and during sleep. A single strand lives for up to seven years.
头发每个月可长12毫米，如果一个人从不剪发，头发会长至107厘米才开始脱落。在夏天和睡觉的时候头发生长得较快。一根头发的寿命可长达7年。
