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Why do we use soap?

Soapy hands under a faucet.
Wash your hands with soap for at least 20 seconds for maximum protection against germs.
(Image: © Hand washing via Shutterstock)

Did you wash your hands? Did you use soap? 

Children everywhere are grossly familiar with those questions, but it's for a good reason: Washing with soap is essential for preventing the spread of germs that make us sick. 

Germs, or microbes, are everywhere. Literally, everywhere. In the air, soil, water and on every surface, including your body. Most microbes are harmless and some are important for human health, like the ones that live in our gut. But there are several germs that cause problems, and these are the ones we prefer not to have on or in our bodies. Our first line of defense against those harmful germs is soap.

What is soap?

Soap is a mixture of fat or oil, water, and an alkali, or basic salt. 

The ancient Babylonians are credited with being the first people to make soap. Their recipe for animal fats, wood ash and water has been found carved into clay containers dating back to 2800 B.C., according to soaphistory.net. They likely used the concoction for washing wool and cotton so the materials could be woven into cloth and not so much for cleaning their bodies.  

The ancient Egyptians developed a similar recipe for soap, which they used for treating sores, skin diseases and personal washing. The Romans also made soap, but it wasn't until the later centuries of the Roman era that soap was used for personal hygiene; prior to that, soap was a physician's tool for treating diseases. 

The basic recipe for soap hasn't changed for thousands of years. It's still a combination of fat or oils with an alkali — basic ionic salt — and water. When those ingredients combine in the proper proportions, they go through a chemical process called saponification, which results in soap. Today, there are two techniques that people use to make soap: the cold process and the hot process. 

In the cold process, a room-temperature lye solution (sodium hydroxide in water) is mixed with animal or vegetable oil. As the ingredients react with one another, the mixture thickens and heats up. Before it gets too thick, the mixture is poured into a mold where it solidifies, and the saponification process is complete. The last step is to let the soap sit, or cure for a few weeks, which allows excess water in the mixture to evaporate. This makes a harder soap, according to the Handcrafted Soap and Cosmetic Guild

The hot process is the more traditional and ancient way to make soap and requires an outside source of heat. The ingredients are heated as they're mixed, which increases the speed of the saponification process. The soap is in a liquid form when it's poured into molds and it's ready for use as soon as it's solidified. Hot-process soap can be cured in a way that's similar to the cold-process soap, but it's not usually needed, according to the Handcrafted Soap and Cosmetic Guild. 

How soap works

Soap doesn't kill germs on our hands, it removes them. 

Germs stick to the oils and grease on our hands (sounds yucky, but it's totally normal). Water alone won't remove much of the germs on our hands because water and oil don't like each other, so they won't mix. But soap likes both water and oil. That's because soap molecules are a type of surfactant, which means they have one end that's water loving, or hydrophilic, and one end that's oil loving, or hydrophobic. 

When you wash your hands with soap, the soap molecules act as a mediator between the water and oil molecules, and bind with both of them at the same time. Then when you rinse everything off, the soap carries away the germs with the water. 

For the most effective hand washing, you must use soap and you must be thorough. Work up a lather because the friction helps lift dirt and oils from your skin, according to the Centers for Disease Control and Prevention (CDC). How long you should scrub depends on how dirty your hands are, but most health authorities recommend at least 20 seconds, or as long as it takes to sing "Happy Birthday" twice. And don't forget to scrape underneath your fingernails. That area is prime real estate for germs. 

Once you've washed, be sure to air-dry or towel-dry. There's no agreed-upon best practice for drying, but wet hands are more likely to spread germs than dry ones, the CDC says. 

Is antibacterial soap even better? Nope. 

Antibacterial soaps have added ingredients like triclosan or triclocarban, which are hydrophobic molecules that can penetrate bacterial cell membranes and kill the bacteria. Sounds impressive, but studies have shown that antibacterial soaps are no more effective than regular soaps at removing bacteria.  

In 2016, the FDA issued a rule that antibacterial soaps were no longer allowed to be marketed to the public. 

"Consumers may think antibacterial washes are more effective at preventing the spread of germs, but we have no scientific evidence that they are any better than plain soap and water," Dr. Janet Woodcock, the director of the FDA's Center for Drug Evaluation and Research (CDER), said in a statement. "In fact, some data suggests that antibacterial ingredients may do more harm than good over the long term."

What about hand sanitizer? 

The CDC recommends cleaning hands with soap and water, but if that's not an option, then hand sanitizer is a good backup. Studies have found that hand sanitizers with alcohol concentrations of 60-95% are more effective at killing germs than nonalcohol or low-alcohol sanitizers. 

Related: Hand sanitizer sold out? Here's how to make your own. 

The alcohol kills some bacteria and viruses by breaking down their protective membranes, which basically makes them fall apart. But it doesn't work for all germs, such as norovirus, Clostridium difficile, which can cause life-threatening diarrhea, or Cryptosporidium, a parasite that causes a diarrheal disease called cryptosporidiosis, the CDC says. Hand sanitizers also likely don't remove harmful chemicals like pesticides or heavy metals, nor does hand sanitizer work well on super dirty or greasy hands. 

Hand washing with soap is, by far, the most effective way to keep harmful germs at bay. 

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