ELI5: Why is washing your hands so effective at preventing illness?

Washing your hands is so effective at preventing illness because soap and water physically destroy germs and slide them down the drain before they can sneak inside your body.

Throughout the day, you touch all kinds of things like doorknobs, toys, pets, and kitchen counters. Without knowing it, you pick up invisible little troublemakers called germs, which include viruses and bacteria. You cannot see them, but they stick to the natural oils on your skin like tiny pieces of glitter. If you rub your eyes, pick your nose, or eat a snack with dirty hands, those germs get an easy ride straight into your body, which can make you sick.

Water by itself cannot get rid of this invisible glitter, just like rinsing a greasy pan with plain water does not clean off the butter. This is why soap is the true superhero of handwashing:

• Breaking the germ bubble: Many bad germs are wrapped in a delicate coat made of fat. Soap loves fat, so it attacks that coat, pops the germ like an overfilled water balloon, and completely destroys it.
• Making hands slippery: Soap is super slippery. It lifts the remaining dirt and stunned germs right off your skin, keeping them trapped inside the foamy bubbles.
• Washing away the mess: When you turn on the faucet, the running water rinses away the soap, carrying the trapped germs straight down the drain where they cannot hurt anyone.

By taking that quick moment to wash up before eating or after using the bathroom, you wipe out the germs before they ever get the chance to make you feel bad.