Why does soap
get things clean?

The full narration of the video.

Does soap get your hands clean because it kills the germs? That's what most of us think. But that's only a small part of the story. Most of what soap does is something else. Let's start with a little experiment. You've just finished a piece of fried chicken, and your fingers are greasy. You rinse them under the tap for ages, and they still feel slick.

Water touches the grease and just slides right past. Oil and water simply won't mix. And that greasy layer is exactly where germs like to hang out. Touch a door handle or a stair rail: the germs cling to the oil on your skin and stay put. That's why water alone can't do the job. Now, add soap.

Zoom into a bit of soap, then zoom again, and it's made of countless tiny sticks. Each little stick has two very different ends. The blue end loves water. The yellow end loves oil, and it hides from water. The oil-loving end dives straight into the grease. The water-loving end stays outside, holding on to the water.

Hundreds and thousands of sticks crowd in: they surround a blob of grease, germs and all, and wrap it into a tiny ball. The outside of the ball is all blue, water-loving ends. So when the water runs, it grabs the ball and carries it down the drain. So were those germs killed on the way out?

Some are. Flu viruses and coronaviruses wear a coat made of oil. The sticks dig in: the coat breaks open, and the virus falls apart. Some bacteria get their outer skin broken too. But many bacteria wear a tough shell, and soap can barely pry it open. They survive, but they still get wrapped up and rinsed away.

One study put this to the test. Twenty people touched door handles and rails in public places: then they either didn't wash, washed with plain water, or washed with ordinary soap, many times over. Unwashed: nearly half the hands carried bacteria that came from poop. Water alone cut that to under a quarter. With soap, it fell below one in ten. What about soap with germ-killing ingredients added? In twenty sixteen, America's drug regulator said: there was no evidence it beats plain soap. And it pulled nineteen of those ingredients out of hand soap.

So soap cleans mostly by tying germs up and hauling them off, not by killing them. The killing is just a bonus. Tying things up takes time. The sticks need to dig in and form those balls, and your hands need to scrub. America's disease control agency says: scrub for at least twenty seconds, about two rounds of Happy Birthday. Next time you wash, picture all those little sticks packing up the germs. Before today, did you think soap was killing germs, or moving them out?