The pH in our skin determines how products are going to respond. pH determines the acidity or alkalinity on a scale of 0 to 14. Anything below 7.0 is acidic and anything above 7.0 is alkaline. Therefore, 7.0 is neutral which actually extends from 6.5 to 7.5.
The pH scale is on a logarithmic scale or it is a 10-fold change in pH. For example, if you have a pH of 8, it is 10 times more alkaline than a pH of 7. If there is a change in two numbers than the change is 100 fold. In other words, the pH of 8 is 100 times more alkaline than a pH of 10.
Our skin has an acid mantle of 4.5 to 6.2. This mantle protects our skin from the many assaults it faces everyday. The acid mantle is made up of sweat and sebum (oil) to protect the skin from certain bacteria and microorganisms. If the acid mantle lowers or rises to much, inflammation occurs. That is why it is important to maintain a healthy skin care regime.
The cleansers that we use on our skin are alkaline. They are generally a pH10. This allows the skin to be cleansed and be in a state to receive the cleaning. If you use soap on your face, and nothing else, then your skin is exposed to all the elements. It has no protection. You will then see comedones (blackheads) or milia (whiteheads) on your skin.