What is Soap: A history and how it works

Kristyn Bango soap

The first evidence of soap is credited to the ancient Babylonians around 2800 B.C. These first soap products were not used for personal cleansing as we do today but in the textile industry and medicinally for skin diseases. 

In the late eighteenth century a better understanding of hygiene and as well as the importance of cleanliness and its relationship to health brought about manufactured bars of soap. Methods for commercial soap, like what we know it as today, came into existence during WWI and became utilized in large production in the 1930's

With such a long history the term soap is now used to describe any products that suds or cleanses. But soap, real soap might be more difficult to find than you think. If you walked into a typical store you would see a wide variety of bars and washes but most of them are not actually soap. These products are classed as detergents. If you looked closely you would notice most of them don’t say soap anywhere on the label.

What is soap?

Soap is what happens after a specific amount of fat and oils, an acid, and a base, solution of sodium hydroxide (NaOH) often referred to as lye and water are combined together go through the chemical process called saponification. As these fats and lye solution come together they begin to saponify, or make soap. Through stirring, the mixture gradually thickens into an emulsion often identified as trace. Chemically what results is classified as a salt.

Traditionally soap was made with rendered animal fat, such as tallow or lard which was readily available on farms. The lye solution was produced by leeching rainwater through wood ash. The solution that resulted varied in the concentration lye which often resulted in a harsh bar the was not very pleasant to use. Today lye is standardized and purchased through mail order in powdered, granule or flakes as sodium hydroxide. Although rendered animal fats can still be used to make soap there are many plant based oils that can be combined to create luxurious bars of soap, and most can be found in your local grocery store.

How does it work?

Once you have a bar of real soap, how does it work to help get you clean? A molecule of soap consists of a chain of carbon, hydrogen, and oxygen, that has a head and a tail. The soap helps the water to wet the surface of your skin and helps the water connect to the dirt and debris that covers your skin. The head is attracted to water while the tail is attracted to the dirt and oil on your skin. These opposing parts connect to the dirt and water together allowing them to be rinsed off of your skin. The soap helps the water to wet the surface of your skin, and helps the water connect to the dirt and debris that covers your skin. 


Got little ones? Try this Pepper and Soap Experiment from Penn Stare to see how soap interacts with water and the importance of hand washing.

What You Will Need

  • Shallow bowl or plate
  • Water
  • Pepper
  • Dish Soap


  1. Fill the bowl or plate with water (until it reaches about 1 inch).
  2. Sprinkle pepper evenly across the surface of the water. 
  3. Stick your finger (without any soap) in the water.
  4. Stick your finger in a small amount of dish soap (you can also use a Q-tip or toothpick).
  5. Predict what will happen once you stick your soapy finger into the water.
  6. Stick your soapy finger into the water.

The Science Behind It

The pepper floats on the water because it is less dense or lighter than the water. Remember the pepper is representing our germs in this experiment. Without any soap on your finger the germs (or pepper) don’t move at all. However, germs do not like soap. The soap is able to surround the germs and take them off of your hands and wash them right down the drain! This is why the pepper ran away from the soap on your finger!

 Experiment Credit: Penn State Behrend 


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