Happy birthday has been sung more times than ever as we all wash our hands even more frequently these days. But it’s for a good reason: Washing with soap is essential for preventing the spread of germs and viruses that make us sick.

Germs, or microbes, are everywhere – literally. In the air, soil, water, and on every surface, including your body. Most are harmless and some are important for health. As we know, though, some can make us sick. Our first line of defense against these is soap.

What is soap?

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

How soap works

Soap doesn’t kill germs on our hands, it removes them. Germs stick to the oils and grease on our hands, so water alone won’t remove them. But soap molecules, which are a type of surfactant, like both water oil. When you wash your hands with soap, the 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.

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.

What about antibacterial soap and hand sanitizer?

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. 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. Hand sanitizers don’t work well on super dirty or greasy hands, so handwashing with soap is, by far, the most effective way to keep harmful germs at bay.