Can Soap Get Dirty?

肥皂會(huì)變臟嗎？

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?

當(dāng)你看到水池邊可愛的檸檬百里香或薰衣草香皂時(shí)，你就知道它能讓你感受到如梔子花香的雛菊般清新動(dòng)人。眾所周知，洗手很重要，但就像毛巾一樣，我們用來清潔雙手的洗手皂也會(huì)變臟嗎?

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 (repelled by water) hydrocarbon chain (the "tail") capped by a polar, hydrophilic (water-soluble) "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.

肥皂僅僅只是由脂肪酸和堿溶液在皂化過程中產(chǎn)生的鈉鹽或鉀鹽的混合物。每個(gè)肥皂分子都是由一個(gè)長而非極性的疏水(被水排斥)碳?xì)浠衔镦?“尾巴”)和其頂端的一個(gè)極性親水(水溶性)碳?xì)浠衔稃}鏈構(gòu)成。由于肥皂分子具有極性和非極性的特性，它們是很好的乳化劑，這意味著它們可以將一種液體溶解到另一種液體中。

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.

當(dāng)你用肥皂和水洗手時(shí)，肥皂分子的尾部會(huì)被水排斥，并被帶有污垢的油脂所吸引。尾部聚集在一起，形成一種叫做膠束的結(jié)構(gòu)，可以吸附灰塵和油脂。這些膠束帶負(fù)電荷，可溶于水，因此它們相互排斥，并分散在水中，極易被沖走。

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.

因此肥皂確實(shí)會(huì)變臟。這就是它清潔雙手的方法：它能比皮膚更強(qiáng)地附著在油脂和污垢上。當(dāng)然，當(dāng)你在使用肥皂的時(shí)候，你是在清洗那些不規(guī)則分布、能吸附灰塵的臟肥皂分子，但是放在浴室臺(tái)上的一塊肥皂或裝在瓶子里的液體肥皂的確可能被微生物污染。

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. (It should be noted that two of these studies were conducted by Procter & Gamble and the Dial Corp., though no contradictory evidence has been found.)

不過，這似乎不是什么大問題。在對(duì)這一問題進(jìn)行的為數(shù)不多的研究中，研究人員給受試者提供了含有大腸桿菌和其他細(xì)菌的香皂，并指示他們洗手。沒有一項(xiàng)研究發(fā)現(xiàn)任何證據(jù)表明細(xì)菌會(huì)從肥皂轉(zhuǎn)移到實(shí)驗(yàn)對(duì)象的手上（值得注意的是，其中兩項(xiàng)研究是由寶潔公司和戴爾公司指導(dǎo)，但沒有發(fā)現(xiàn)相互矛盾的證據(jù)）。

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，臟肥皂不能自潔。一塊被污染的肥皂可以通過洗手時(shí)清潔的相同機(jī)械作用得到清潔：良好的傳統(tǒng)擦洗。雙手與肥皂摩擦產(chǎn)生的摩擦力，以及自來水的沖洗作用，會(huì)清除手上和肥皂上的有害微生物，使其流入下水道。

翻譯：MS小冰晶