About Soap and Why It Works
The short answer is because cleanliness is next to godliness, but the long answer is pretty cool too, in a Mr Wizard kind of way.
Soap is made up of long molecules that attach themselves to oily and grimy surfaces.
Each end of these long molecules behave differently. One end is attracted to water, while strangely enough, the other end is repelled by it, not unlike a magnet. As a result, those long soap molecules come together and form “droplets.” The ends of the molecules that are attracted to water face outward, thus separating the dirt from the water.
A Brief History of Soap
No one knows where or when soap was first invented, but we do know that it has been around for a long time.
The first evidence of soap dates back almost 6,000 years to ancient Babylon, but different recipes have been found dating back over 5,000 years. The earliest ones involve animal fat and ashes, but later ones substitute various different oils for the animal fat. The Romans were known to add urine because the ammonia it contained is actually a very effective cleaning product.
At some point plants were found to contain a chemical called saponin that could be used to make soap. Over 100 different types of plants contain the chemical that, when mixed with water, creates a foam that lifts off dirt and grease. In North America, native people used the root of the Yucca plant and in India, a shrub called the soap nut bush was used. This technique became very popular and by 1200 AD, soap was being made in Bristol and 200 years later in Spain with olive oil.
This process developed over the years, and although some companies now use man-made chemicals, others still use natural ingredients from plants. Soap is now produced in both solid and liquid form and comes in a variety of shapes, colors, and smells. And of course, a wide variety of additives produce abrasive soaps, scented soaps, hard or soft soaps, and so on.