Q1: How does soap work?
Castile soap and shampoo bars are both soaps. I guess there is an expectation that soap works differently from shampoo but it does not. Soap and shampoo clean with the same principle. They both contain surfactants which can dissolve oil (I will link the surfactant article only once today lol...here it is). In actual fact very similar to SLS, soaps are anionic (meaning negatively charged) surfactants.
Q2: Are soaps milder than shampoo?
Not necessarily (Journal of the American Academy of Dermatology, pp 35-41, 1979). Irritation of the skin is based on removal of oil from the skin. The oil layer removal causes dryness and itching. The more effective the soap or shampoo is at removing oil, the more irritation it will cause.
Q3: Is soap an effective cleanser?
Yes soap is an effective cleanser with a proviso. Soap works best with soft water. Hard water contains minerals such as calcium which react with the soap. This creates what we know as soap scum which is quite difficult to get rid of. As long as you have soft water, soap is an effective cleanser.
Q3: What about the fact that soap is alkaline?
This is an interesting point and I will discuss it tomorrow so as to avoid making this article overly long. Yes skin and hair are slightly acidic while soap is alkaline (talking traditionally made soap like castile soap - it is possible to have synthetic soap which is neutral or acidic). Tomorrow we will look at this pH story in detail, namely
1. Is there scientific evidence that pH can raise or close cuticles?
2. Is there scientific evidence that pH can cause relaxing of hair?
3. Is there scientifc evidence that pH can irreversibly damage skin or hair?
Image Credit: Dr. Bronner's on Amazon