Working out how hand-washing actually works
Washing your hands is important, and the easiest way people can stop the spread of many diseases, let’s get that out of the way. We’re taught the importance of soap and water from a young age, and most a few of us make it a habit of doing so when we’re near the sink. As a parent trying to promote this healthy habit with my kids, I’ve nagged them about water not cutting it, and that they need to wash with soap for at least one round of the Happy Birthday song before they’re done. As a diligent nerd though, I’ve found that some of the above really isn’t that simple, and that I’ve only sort of understood what all the water and bubbles were really about.
Soap is a pretty old invention, dating back to Babylonians that washed with a mixture of fats, ash and water. The premise, even in this more primitive recipe, was that soap helps break up the surface tension of water droplets, helping water get into every nook and cranny in your skin. Once the water reaches a bit of dirt or cluster of microbes, it can carry it away from your skin. Soap isn’t fighting the germs directly, but it prevents infection by helping water clean those germs off your skin.
Washing with just water
This is where the role of soap gets a little murky. A study in rural Bangladesh followed people’s hygiene habits and compared them to rates of children’s diarrhea in the household. In that study, the biggest health gains were made by people that washed both hands with just water. Adding soap to the mix helped, further lowering rates of gastric distress, but it didn’t make as much of a statistical difference as washing with water did. For as many times as I’ve sent my kids back to the sink to use soap, I realize that if soap is basically a way to enhance what the water is doing, it makes sense that soap is really just the icing on this hygiene cake.
However, to further complicate things, it’s important to also consider that not all soaps are limited to lowering the surface tension of water. Products that are technically detergents, although many get used and called soap, offer the extra benefit of being a surfactant. A surfactant also helps lower water’s surface tension, but the shape and chemical properties of these molecules also helps them take apart fats called lipids. One end of a surfactant molecule is attracted to water, while the other avoids it, and more easily bonds with dirt or grease. When up against germs, these properties can also allow surfactants to break up the cell membrane on bacterial cells, giving them a more direct role in keeping our hands from carrying too many potential pathogens.
If this didn’t make things messy enough, consider that there are also soaps you probably don’t want to use in the first place. Soaps marketed as ‘antibacterial’ were made with poisons like triclosan or triclocarban. Rather than clean surfaces, these ingredients were meant to kill bacteria, however they were never found to really leave the end user any better off than regular soaps. Because they also posed a risk of pushing bacteria towards antibiotic resistance, the FDA has actually banned these products. Alcohol-based hand sanitizers also try to kill microbes on the skin, and are actually effective. The problem there is that if you used them every time you washed, or should wash, your hands, it would be very hard on your skin. The last soap to avoid is just dirty soap. Since many soaps wash away rather than destroy germs, they can actually harbor germs and end up spreading them on your hands while you try to get clean.
So is it time to give up on all this, and join the multitudes that aren’t washing their hands? Nope— there are real benefits to clean hands, but it’s just a matter of doing it right. Washing your hands works best if you use (clean) soap, ideally with hot, soft water. The hotter water helps break up water’s surface tension, and soft water with fewer minerals in it helps soap get rinsed away without leaving residues. When you’re washing your hands, make sure to lather the soap and actually try to, you know, wash them. Rub between your fingers, on the backs of your hands, etc, as that mechanical process will help loosen more dirt and microbes. Washing should include at least 20 seconds before you rinse with clean water. People usually wash longer if they’re focused on making soap bubbles, which is another way that soap helps us clean our hands. Then do your best to dry your hands without grabbing anything else that might undo your hard work, such as nearly anything my four-year-old has been near in the last 30 minutes.
Source: Simple Science: The Difference Between Soap and Detergent, Nyco Products.com