Anne says…Real soap is NOT problematic for all people, either on skin or on hair. Many just don’t like the feeling on hair, but if you happen to, just use shampoo every few washes to prevent buildup. And as for skin, many people have zero problem with a high pH wash off product. For those who do, there are other options yes. Sad to see this answer jump onto the bandwagon of disregarding soap without a full answer, and it just isn’t the whole truth to say that “Regular soap is not good for skin”.
The Beauty Brains respond:
Anne’s comment comes to us from our recent post on using bar soap on hair. I agree that my original answer wasn’t detailed enough so I’ll try to correct that here.
I certainly don’t blame Anne for defending bar soap since she’s affiliated with Dot & Lil, a company which sells vegetable oil based soaps. But it’s well documented that soap is more drying to skin than surfactants. In fact, plain old ivory soap is used to dry out skin in moisturization testing!
Soaps and synthetic surfactants can dry skin
Of course that’s not to say that surfactants are perfect and that they do no harm. Anything which solubilizes oils has the potential for stripping the skin. Some surfactants, like sodium lauryl sulfate, don’t rinse well because they can interact with skin protein. The residue they leave behind is irritating so some people.
BUT, surfactants (which typically have a pH in the range of 5-7) do not upset the skin’s acid mantle as much soap which has a pH in the range of 9-10. If the mantle is washed away or neutralized by alkaline agents then the skin is more easily damaged or infected. That’s because, without the mantle, the skin cells start to separate and allow more moisture loss which in turn causes tiny cracks in the skin where bacteria can enter. Once the mantle is depleted and the pH of skin gets above 6.5 you’re much more prone to damage and infection.
There are number of studies such (see below) that have evaluated the harshness of cleansers and have consistently found that soap is worse than surfactants.
The Beauty Brains bottom line
All cleansers have the potential to strip oils from your skin but soap has been shown to be more drying, harsher, and more disruptive to the skin’s protective acid mantle than many surfactants.
References
Interactions of cleansing bars with stratum corneum proteins
Journal of the Society of Cosmetic Chemistry 46, 301-320 November/December 1995)
Forearm wash test to evaluate the clinical mildness of cleansing products
Journal of the Society of Cosmetic Chemistry 39, 355-366 (November/December 1988)
Soap and detergent bar rinsability
Journal of the Society of Cosmetic Chemistry 37, 89-97 (March/April 1986)