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Thanks for the advice.

Tonight, I did a search for research articles on irritability and skin damage.  You can see a list of the articles I found that compare surfactants at:

https://www.ncbi.nlm.nih.gov/pubmed/?term=SODIUM+COCOYL+ISETHIONATE
 
(Or go to pubmed.gov and type in sodium cococoyl esthionate (ISE) like I did)

What was interesting to me, in most of these studies, is that ISE was almost as irritating as SLS and required almost as long for skin recovery as SLS.  (So why then is ISE advertised as more mild, when research shows it’s so similar?)

What was also interesting was that the aionic surfactant, disodium laureth sulfosuccinate (SUL), was the least irritating, even less than cocamidopropyl betaine (CB) and the glucocides.

So this made me think of more questions:

These studies in the 90’s did not test SLSa (Lathonal).  Do you think it would be similar to SUL?

Do you think one could make a shampoo with only SUL or SLSa, plus some CB?

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Thanks for the replies.

The interesting thing is that the rest of my skin doesn’t seem to be particularly sensitive.  I have no problems with hand soap, or shaving gel or colognes.  There must be something different about the scalp environment.

The problem with modern shampoos is that in an effort to create the perfect product, they have added 15-20 or more ingredients.  This makes is really challenging to isolate which one (or more) of these ingredients are causing the sensitivity.  This is why I thought instead of trying to figure out which ingredients, among many, are the problem, that it would be nice if I can only start with one or two. 

I also have a co-worker that has a very sensitive scalp.  I am surprised that no one is making a “naked” shampoo with only one or two cleaners and nothing else, for people like us.  I bet there would be a small market for it.

If I create a solid bar with little to no water and it completely dries out between uses, is it still necessary to include a preservative?

It seems most shampoos include a small amount of fat, is there some reason why this is necessary or is this optional?