Buzz
When you spot charming bars of lemon-thyme or lavender-scented hand soap by the sink, they seem designed to lift your spirits, making you feel as fresh as a flower blooming in a garden. We all know that hand washing is essential, but have you ever wondered if the bars of soap we use to cleanse ourselves, like washcloths and towels, can also become dirty?
Soap consists of mixtures of sodium or potassium salts, which are derived from fatty acids and alkali solutions during a process known as saponification. Every soap molecule has a long, hydrophobic (water-repellent) hydrocarbon tail and a polar, hydrophilic (water-soluble) head that is essentially a "salt". Due to its dual nature, soap acts as an excellent emulsifier, enabling it to blend one liquid into another.
When you scrub your dirty hands with soap and water, the hydrophobic tails of soap molecules avoid the water and instead attach themselves to oils that hold onto dirt. These tails then form clusters called micelles, which trap the dirt and oils. The micelles are negatively charged and water-soluble, allowing them to repel one another and stay dispersed in the water, making it easy for them to be rinsed off.
Yes, soap does get dirty. In fact, that's part of its job: it clings to grease, dirt, and oil more effectively than your skin does. While you're washing your hands, you're rinsing off the soap's dirt-attracting molecules. However, a bar of soap on the bathroom counter or liquid soap in a bottle can still pick up microorganisms.
However, this doesn't appear to be a significant issue. In the few studies conducted on this topic, test subjects were given soap bars contaminated with E. coli and other bacteria and told to wash their hands. None of the studies found any evidence of bacteria transferring from the soap to the subjects' hands. (It's worth noting that two of these studies were conducted by Procter & Gamble and the Dial Corp., but no conflicting results have been reported.)
Soap can't clean itself, though. A contaminated bar of soap is cleaned the same way it helps clean you: through good old-fashioned scrubbing. The friction of your hands rubbing against the soap, combined with the flushing action of water, helps wash away any harmful microorganisms from both your hands and the soap, sending them down the drain.
This story was updated in 2019.
