Can Soap Get Dirty?
肥皂会变脏吗？
When you see lovely little bars of lemon-thyme or lavender hand soaps on the rim of a sink, you know they are there to make you feel as fresh as a gardenia-scented daisy. We all know washing our hands is important, but, like washcloths and towels, can the bars of hand soap we use to clean ourselves become dirty as well?
当你看到水池边可爱的柠檬百里香或薰衣草香皂时，你就知道它能让你感受到如栀子花香的雏菊般清新动人。众所周知，洗手很重要，但就像毛巾一样，我们用来清洁双手的洗手皂也会变脏吗?
Soaps are simply mixtures of sodium or potassium salts derived from fatty acids and alkali solutions during a process called saponification. Each soap molecule is made of a long, non-polar, hydrophobic hydrocarbon chain capped by a polar, hydrophilic "salt" head. Because soap molecules have both polar and non-polar properties, they're great emulsifiers, which means they can disperse one liquid into another.
肥皂仅仅只是由脂肪酸和碱溶液在皂化过程中产生的钠盐或钾盐的混合物。每个肥皂分子都是由一个长而非极性的疏水碳氢化合物链和其顶端的一个极性亲水碳氢化合物盐链构成。由于肥皂分子具有极性和非极性的特性，它们是很好的乳化剂，这意味着它们可以将一种液体溶解到另一种液体中。
When you wash your dirty hands with soap and water, the tails of the soap molecules are repelled by water and attracted to oils, which attract dirt. The tails cluster together and form structures called micelles, trapping the dirt and oils. The micelles are negatively charged and soluble in water, so they repel each other and remain dispersed in water—and can easily be washed away.
当你用肥皂和水洗手时，肥皂分子的尾部会被水排斥，并被带有污垢的油脂所吸引。尾部聚集在一起，形成一种叫做胶束的结构，可以吸附灰尘和油脂。这些胶束带负电荷，可溶于水，因此它们相互排斥，并分散在水中，极易被冲走。
So, yes, soap does indeed get dirty. That's sort of how it gets your hands clean: by latching onto grease, dirt and oil more strongly than your skin does. Of course, when you're using soap, you're washing all those loose, dirt-trapping, dirty soap molecules away, but a bar of soap sitting on the bathroom counter or liquid soap in a bottle can also be contaminated with microorganisms.
因此肥皂确实会变脏。这就是它清洁双手的方法：它能比皮肤更强地附着在油脂和污垢上。当然，当你在使用肥皂的时候，你是在清洗那些不规则分布、能吸附灰尘的脏肥皂分子，但是放在浴室台上的一块肥皂或装在瓶子里的液体肥皂的确可能被微生物污染。
This doesn't seem to be much of a problem, though. In the few studies that have been done on the matter, test subjects were given bars of soap laden with E. coli and other bacteria and instructed to wash up. None of the studies found any evidence of bacteria transfer from the soap to the subjects' hands.
不过，这似乎不是什么大问题。在对这一问题进行的为数不多的研究中，研究人员给受试者提供了含有大肠杆菌和其他细菌的香皂，并指示他们洗手。没有一项研究发现任何证据表明细菌会从肥皂转移到实验对象的手上。
Dirty soap can't clean itself, though. A contaminated bar of soap gets cleaned via the same mechanical action that helps clean you up when you wash your hands: good ol' fashioned scrubbing. The friction from rubbing your hands against the soap, as well as the flushing action of running water, removes any harmful microorganisms from both your hands and the soap and sends them down the drain.
然而，脏肥皂不能自洁。一块被污染的肥皂可以通过洗手时清洁的相同机械作用得到清洁：良好的传统擦洗。双手与肥皂摩擦产生的摩擦力，以及自来水的冲洗作用，会清除手上和肥皂上的有害微生物，使其流入下水道。
