to make skin-friendly soap is hard. Vegetable or animal source fat differs from batch to batch. Differing composition due to source and amount of vegetable matter, animals, type of animals. A chemist has to get a sample of the bulk mix of all rendered fat in the reaction vat, hopefully more than 1000 gallons.
Titrate the sample with sodium caustic, which in the industry is about 55% solution. Or caustic potash, 45% solution. Scale up the amount of the caustic, add to the vat on the low amount side. Watch the consistency, take pH. No possibility for sodium or potassium-based soap to attain the gentleness of baby shampoos. Once the fat-caustic based soap is used for washing, the fatty acid does its job of suspending the soiling matter, uncoupling from the +OH hydroxide ion, since the pH of tap water is different from the soap's optimal pH, and the +OH ion contributes to the excess of alkalinity of water, and all together attacks skin.
Ionic soaps which are more friendly to the skin use weaker bases, like amines, and the resultant acid-base is more natural to the tap water pH.
But non-ionic soaps are still the best. Labelling still can't be interpreted as chemically correct. "Non-soap" may mean non-ionic, or non-ionic surfactant, or it could mean cationic surfactant, in either case it's a high-tech product optimized for right pH in the wash.
Last time i checked the Fa brand soapless soap was the best. Other than baby soaps.
