Soap, we use it every day and yet it is often taken for granted. Can you imagine life without it? According to the World Health Organization 1/3 of childhood diseases causing death before age five could be prevented by using soap! But how could access to simple hygiene products make a difference? First, we need to know more about soap. What is soap? How does it work?
How Soap Works
The story of soap actually begins with water since soap alone will not wash away dirt. Water molecules are made up of one oxygen atom and two hydrogen atoms. The hydrogen atoms are on one side of the molecule and the oxygen atom is on the other side. There is a positive charge on the hydrogen side of the water molecule and a negative charge on the oxygen side. The positively charged hydrogen end of each water molecule is attracted electrically to the negatively charged end of other nearby water molecules. This attraction causes countless temporary bonds between water molecules, which, in turn, makes a body of water in a glass, bathtub or lake.
Within a container, or even a drop of water, these bonds create a pull on all the molecules in every direction- except at the surface. The molecules at the surface have no molecules above them to pull on them, so they are only pulled by the molecules underneath them. This creates surface tension, making it possible to fill a glass noticeably above the rim. It also holds dew drops together in little spheres.
Water strider insects can actually skim around on the skin-like surface of ponds and streams because of surface tension.
Water will dissolve sugar or salt, as their particles also have electrical charges, but dirt is usually associated with oil, and water is simply not attracted to oily things because oil does not have an electrical charge. In fact, water and oil repel each other. If you put a greasy dish into water, the grease will actually flatten itself against the plate to get away from the water molecules.
Soap changes the chemistry, starting with the surface tension. A soap molecule is a long hydrocarbon chain that looks a bit like a caterpillar. The head end loves water and hates oil, the tail end loves oil and hates water.
When soap is added to water, the soap molecules near the surface squeeze between the surface molecules of the water and all stand on their water-loving heads with their water-fearing tails in the air. Soap in water will reduce the surface tension of the water to about a third of its usual strength. Soap bubbles last longer than plain water bubbles because there is too much surface tension in water for it to remain in a bubble. In a soap bubble, the tails of the soap molecules are on the outside of the bubble, which also protects the bubble from evaporation. If you want to see how long you can keep a soap bubble, try putting it in a jar. One bubble lover kept a bubble for 341 days this way.
Soap that is dispersed in water forms little clusters called micelles, as a group of soap molecule “caterpillars” get together with their tails in the center of the cluster away from the water. This gives the clusters a negative charge, so they repel each other and disperse throughout the water. When they encounter a bit of grease or oil they grab it and form a new micelle with the grease held inside the micelle. These particles are washed away when we rinse the soapy dishes.
Washing a person is similar to washing dishes given that water alone does not clean the dishes and we are oily or greasy, just like the dishes. Our Skin has natural oil called sebum. Dirt embeds into sebum, and the dirt/oil mixture repels water until soap is applied. But wait, how does soap actually clean oil, dirt and grease?
Soap is made by combining fats and oils containing fatty acids with lye, which is alkaline. The strong alkali in lye splits the fats/oils into fatty acids and glycerin which is another chemical reaction. Then, the sodium (or potassium) part of the alkali joins with the fatty acid part of the fat or oils, forming a salt that we call “soap”. If soap is not made with lye (sodium or potassium hydroxide) and oils it is not soap, although when properly made there will be no lye in the final product. Lye is a catalyst, although the sodium or potassium, oxygen and hydrogen atoms that make up lye are still present at the end of the chemical reaction, it is in a form that is not harmful.
Using soap will remove some of our natural oil and the dirt and that attaches to it. Soap also removes bacteria, viruses and other potentially harmful microorganisms. Although we are a host to many friendly microorganisms that keep us healthy, washing with soap keeps us in good health by helping to remove the unwanted harmful microorganisms. Washing our hands with soap is the most effective way to remove the harmful germs and prevent the spread of disease.
Atom- The smallest indivisible particle of any gas, liquid or solid.
Molecule- A group of elements bonded together that create the smallest unit of a compound. The most known of these is H2O or water. H2O means there are two atoms of hydrogen and one atom of oxygen to create the smallest unit of water possible.
Surface tension- The property of the surface of a liquid that allows it to resist an external force.
Micelles- A cluster of soap molecules that can trap grease and oil.
Sebum- The fatty substance secreted by the sebaceous glands of mammals that protects and lubricates the skin and hair.
Alkaline- Having a pH greater than 7, a salt, a base.
Microorganisms- a microscopic organism, especially a bacterium, virus, or fungus.