Soap as a shampoo?
So who is right? And can we easily tell?
I have some personal experience, but I wanted to gather as much information as I could on the subject… and I share all I know so far with you…
It is very attractive – soap as a shampoo! … it can be made easily at home and if you select the right oils, like castor oil or jojoba oil – as suggested in many recipes for soap shampoos – it must work!
Let’s get rid of commercial shampoos full of dangerous Sodium laureth sulphate and open the gates for simple soap!
If only it was that easy…
A little bit about hair structure
Hair has a complex structure and it is covered with keratin cuticle. Keratin is a protein and proteins are by nature acidic (pH<7). This means it does not like alkaline conditions (pH>7). It changes its conformation as acidic bonds within keratin change and keratin layer opens.
Here are some bites of information I have mined so far from different sources – funny, the best sources seem to be patent applications, always summarizing the state-of-the-art knowledge. We can make kind of a shampoo evolution from those, which I did – see below. But I am continuously searching for scientific references…
Alkalinity and (soap) shampoo evolution …
The idea of soap as shampoo is not new, actually, in the first edition (1923) of Poucher’s book Perfumes and Cosmetics, with especial reference to Synthetics, the shampoos, except for the dry shampoos, are all based on soap, and formulated using soap powder or made in situ from alkalis and natural oils.
Later, with new no soap detergents being available, soaps are quickly forgotten. However, it seems that still in 1940’s the detergents are mainly alkaline, to cite the European patent application http://www.freepatentsonline.com/EP0437114.html
The use of citric acid in hair compositions has long been known, for example, US 2 255 341 refers to a “lemon” hair rinse, used to restore an acid pH, following the more alkaline shampoo treatment generally used in the 1940’s.
Here we see that applying acidic rinse was wildly used in order to restore natural hair conditions…
With long hair mode in 1960s, it becomes evident, that alkaline shampoos damage hair – to cite J. Grey 
When long hair became more popular in the 1960s, there was an upsurge in demand for shampoos that could be used frequently. The anionic surfactants of the time, at often alkaline pH levels, tended to strip sebum and damage the cuticle…
… I just would like to know why it took men long hair to realize this…
In consequence, alkaline detergents are therefore not a good choice for damaged hair, as the US patent US3996146 from 1976 states:
The acid pH, clear shampoo formulation of this invention is especially beneficial for damaged, bleached or cold-waved hair. The deleterious effects of shampooing damaged hair with alkaline detergent systems are avoided by maintaining the clear shampoo formulation within the acid range.
It seems that alkalinity is a big NO for hair skin with medical condition (dandruff), and that if using an alkaline shampoo, a separate acidic treatment must be used after such a shampooing, as described in the US patent application from 1992 US5132107:
It is assumed that the substance of the corneum (the protein keratin) through a normal alkaline shampoo obtains a “woolly” stereochemically open surface structure, which is advantageous for cleansing, but also promotes reinfections and growth of established skin flora. This has as a consequence for instance that dandruff is quickly reestablished and is returning regularly irrespective of the treatment with such a shampoo…
It has been foud that by a subsequent second treatment with an acid rinsing liquid surface proteins of the skin can be made to coagulate by which they obtain a “closed” stereochemically densely clustered structure… at the same time a more natural pH is obtained.
From the above, we can also read, that skin keratin reacts by changing its structure to woolly and open surface. We can assume that similar thing happens on the hair (I am searching for a scientific journal source of this statement…).
From the above it is clear that we do not want alkaline things on our head and hair. If we do, we’d better use some acidic rinse, like vinegar.
ATTENTION – the acidic rinse can be quite fun to make – do not try to pour over your head simple table vinegar, you wouldn’t be very happy about the smell and it is also unnecessarily strong…
Rather play around with different herbal infusions, to which you add a bit of vinegar. pH meter can help to find out how much you need.
One would believe this is it, HOWEVER. there is another important factor to consider:
Soap creates with calcium and magnesium ions of hard water so called SOAP SCUM. It is very difficult to rinse it from anywhere, imagine from your hair!
So what happens when you shampoo with soap in hard water?
- Because of soap alkalinity, your keratin will change to “woolly” stereochemically open surface structure
- Soap will create scum with hard water – already difficult to rinse per se (have you ever seen the nice bath tub ring after bathing with soap?)
- Because of the open surface structure of keratin, soap scum will even more attach to hair
You can imagine what happens if you have in addition DAMAGED hair… I can say, as my hair was once bleached and very damaged and I lived in a region with hard tap water. My hair grew out, so I enjoyed a bit more soap shampooing with hard water, however, the best it is now – we have moved to a region with soft tap water.
Over all conditions, my bleached and damaged hair did not really like soap shampooing – whatever hardness the water was.
Make an experiment
Buy a bottle distilled water and try once shampooing and rinsing with your tap water and once with distilled water. If your tap water is hard, you will definitely feel the difference!
Is soap shampoo right for you?
Here is a small scheme I have created, based on my personal experience, discussions from forums (personal experience of others) and all I have studied about the subject so far.
Please, take into account that finally it can be very individual. I guess there might be much more conditions to take into account. If I write “you might like it”, that does not mean it is good for your hair in long term!
I would love to read your opinion and your experience, please, leave me a comment below!
 Gray, J. Hair Care and Hair Care Products. Clinics in Dermatology 2001;19:227–236