The Chemistry of Cleaning
The key to the chemistry of cleaning is that salts have two ions - one that is strongly attracted to water (water-loving), and one that is not attracted to water (insoluble). When salt is added to water, the water loving ion attaches to water molecules (dissolves). It then has an "unattached ion" that is actively attracted to substances that water is not naturally attracted to, like air and dirt.
Substances that have this dual attraction from water-loving and non-water loving components are called "surfactants" (surface active agents). The term "surface" in this phrase refers to the surface tension of water. We see it as in water droplets, or when you fill a glass just a wee little bit too full but it doesn't overflow. Surfactants break that water tension and cause water to spread out by creating a chemical "bridge" that pulls the water along to places the water would not normally go. There is a very excellent description of this process here.
Soap bubbles are formed when certain surfactants come into contact with air. Air molecules get connected to one end (the non-water loving end) of the surfactant. Water gets connected to the water loving end of the surfactant. The surfactant molecules join together like tiny magnets in a circle, effectively "capturing" the air. This causes water to spread out REALLY thin around the outside of the circle. Voila! Bubbles!
Bubbles push the dense water out and spreads it across a larger area. Then, any dirt that is water soluble comes in contact with the water and is dissolved.
Like the air molecules, non water soluble dirt molecules are also attracted to the non-water loving ions. The surfactant molecules surround the dirt in the same way as the air. Soap does not actually destroy or modify the dirt molecules, but breaks up dirt clumps in to small chunks and them imprisons it in a cell of water.
Both air and dirt are "captured" in this fatal chemical attraction. We call it cleaning. Conveniently, soap bubbles facilitate the spread of soap and water, allowing more dirt molecules to be captured along the way. This is why lather is good for cleaning.
The Mechanics of our Skin
Skin is kinda gross. What we call skin is a layer of dead cellsin a waxy base. Yuck. But there it is. That waxy part is what causes us to need to cleanse ourselves with soap.
As mentioned in an earlier post, some critters that inhabit our bodies do us good. Some do not. Our chemical and immune systems know the difference. Invaders are kept out by the system that holds our skin together. Our beneficial cohabitants are somewhat protected by our physiology. In short, when our skin is working, there are carcasses of dead invaders all over us. Yuck again.
Another fun fact about our waxy outer layer is that it attracts other waxy things. Grease, other waxy substances in our food and environment. Greasy things stick together. So along with carcasses, we have spare grease on us. Um, did I say Yuck yet?
Now assuming you are not fixing cars or using other petroleum based substances on a regular basis, this is the extent of our body dirt.
How do we get this stuff off of ourselves? You guessed it, we use salt surfactants.
Types of Surfactants
Soap is a surfactant, but not all surfactants are soap. The behavior of the salt depends on what chemicals are used to create the water loving and non-water loving ions. The definition of "soap" is that it is made from triglycerides, which are the fatty acids found in plants and animals, and a strong base. These chemicals occur naturally.
Non-soap surfactants are made from synthetic chemicals of all kinds, but mostly what we know as "detergent" is petroleum based. These detergents are very popular because of their strength in breaking down organic dirt. The problem is, detergents see our natural skin oils as just more dirt, and removes every bit of it.
This distinction is also important if you care about what you put on your skin. It has been discovered that what we put on our skin does sink in to our bodies. Periodically, rules about what chemicals can be used in detergents are instituted based on observations of damage or health risk, such as this recent rule change about phosphates in dishwasher detergent.
If you search the cleaning chemical industry materials, there is much discussion about using the cleaner that is right for the substance being removed and the surface being cleaned. Here is an example of a floor cleaning site that talks about protecting the surface AND your health by understanding the chemicals being used. SMART!
There are many other cleaners out there - chelating agents, solvents, strong acids and bases…. All have their use. Some cleaners do more than one thing. A common practice is to add a chemical that assists in transporting the cleaning agent deeper into the surface being cleaned.
Soap is for Humans
The saponification process just happens to create a surfactant that is appropriate for cleaning human skin. Properly made soap is strong enough to remove the very outer layer of our waxy selves and all the environmental grease and get rid of any bad bacteria, but does not penetrate the lower layers of our skin. It leaves our outer surface refreshed and healthy. By coincidence, one of the byproducts of the saponification process is glycerin - which attracts extra water for our skin. This allows our protective system to hydrate and refresh itself after cleansing.
Synthetic detergents are man's imitation of this natural cleanser called soap. Detergents are formulated to go deeper than soap. The process of making detergents necessitates chemical additives to make the product behave the way the manufacturing equipment needs it to.
To compensate, formulas are made to include moisturizers to that are man's attempt to emulate the action of glycerin (glycerin is considered too precious to include in soap). More chemicals are needed to preserve the additives that compensate for the overly aggressive cleaning action. This is why the list of ingredients in your cleanser is an unintelligible chemistry lesson.
The decision about what type of bathing cleanser to use should invoke some of the same thought processes as choosing your chicken (or plant protein, if you are vegetarian). You can buy chicken patties, which started out as chicken meat, and are then processed beyond recognition with chemicals and preservatives into a standard, convenient form (or buy soy meat-shaped items). Or you can buy chicken (or tofu), which is the actual food product being imitated by chicken patties.
Detergents will clean you, and they are cheap, but soap is the real thing for cleaning human skin. Handmade soap with all the natural ingredients intact and not processed beyond recognition is more than just a luxury - it is truly caring for your skin.
Good strong detergents are good for some things. Like in the washing machine. Cotton garments and other natural fibers might be worn down by the attack of the detergent, but they are just clothes. Torture your skin like you torture your jeans, and you may find skin is harder to repair and replace.