Not All Soaps are Created Equal

Not All Soaps Are Created Equal - 10 February 2017

A little while ago someone mentioned to me that they were using an inexpensive brand of supermarket soap and their family’s skin was having trouble with it. This set me thinking and I did a little investigation to figure out what was going on.

There are two main types of soap you can buy in your average New Zealand supermarket - either a detergent (often marketed as a “soap alternative” in Chemists) or soap. Broadly, the cleaning agents in them work by breaking down grease and making it easier to rinse off. They are both biodegradable in their pure form.

A detergent isn’t a bad chemical at all. Detergent is a catch-all phrase for a chemical that cleans grime. It is made of a long hydrocarbon chain with a sodium atom at one end, usually constructed from petroleum products, a foaming agent and alcohol. It is great for cleaning such as washing dishes and in situations where water is very hard. It is easy and cheap to make in the high volumes that the modern world demands. Where manufacturers want to use it to clean skin, they include ingredients to mask scent, moisturise skin and stop fungal or bacterial growth – and this is where the problems start for people with sensitive skin. Not only may they be sensitive to the detergent, but they may be sensitive to the additional ingredients put in to make the soap more usable. The only way to avoid this issue is to stop using soaps where the main ingredient is listed as detergent. New Zealand labeling laws can be confusing - if in doubt ask the manufacturer. My friend was already avoiding such soaps, so that wasn’t her problem.

The soap she was buying from the supermarket stated it was a true soap, not a detergent. Soap is made from fats, oils, lye (a very strong alkali that forms soap when mixed with fats and oils) and water. It has a slightly different chemical arrangement to detergent that means it is generally not as harsh, but it doesn’t dissolve entirely in hard water and so forms a cloudy scum. Modern soap makers are extremely careful about the proportions of lye in their soap, so we can rule out lye burns as the reason soap upsets skin. What else could cause it?

It turns out not all soaps are created equal. At the high end of the market they are handcrafted from scratch in small batches from pure fats and oils. If you can afford to use these every day you are very lucky. At the low end, they are made from pre-made soap “noodles” or “seeds” that are melted down to make soap bars. The quality of soap seeds varies depending on the quality of fat or oil they were originally made with, the amount of glycerol left in and the amount of time the soap was boiling while the glycerol was being removed.

The main difference between the two is glycerol. This is the chemical that gives soap its moisturising properties and means soap makers don’t need to add the moisturisers that are in detergent. Mass produced soap seeds have the glycerol that is formed when soap is created removed and used for other purposes – ironically, one of them is to make the moisturisers that you need to buy for the dry hair and skin created by your cheap soap. Handmade soaps leave the glycerol in; in fact, it’s difficult to remove without the right equipment.

Soap made from soap seeds is what was creating the skin problems for my friend. After using many types of soaps and going through a careful process of elimination, she solved her problem by inspecting the labels on the soap she buys for ingredients such as detergent, added glycerol and soap seeds. This costs her more in soap ($10 v $3), but less in moisturiser, conditioner, doctor’s visits and hydrocortisone. Overall, she has a considerable cost saving and a much happier family.