How Does Soap Work, Anyway?

Soap’s been around a long time, at least six thousand years, but how does it get that spot of gravy off your favorite shirt?

A molecule of soap is a long chain of carbon and hydrogen atoms with some oxygen atoms tacked on at one end. The end with the carbon and oxygen likes to attach to water molecules and the other end, which is just hydrogen and carbon, likes to attach itself to oils. This oil the carbon-hydrogen end likes so much is what can make dirt mixed with it so hard to remove because the oil likes to stick to the fibers of the material in your shirt.

When you dissolve soap in water the oil loving ends attach to the oil in the gravy stain and the water loving end (the end with the oxygen), attaches to a water molecule. Usually what happens is that a bunch of soap molecules surround the oil to form a glob of soap-oil-dirt with the dirt-oil in the middle of the glob and the water loving ends of the soap molecules sticking out hanging on to the water. Now when you stir things up, like when you slop your shirt around in the soapy water, the soap and oil glob is lifted from the shirt and suspended in the wash water.

When you rinse your shirt, the soap-oil-water combo is washed away and hopefully you have a clean shirt and no one will ever know you dripped gravy on it.