Conditioners replace some of the natural oils, reduce tangling and make the hair shinier and easier to comb. Additives are put in shampoo to meet a particular need, such as to control dandruff. The pH of a shampoo has become an important factor in selecting the right shampoo for the right type of hair. The scale of pH is measured between 0 and 14. A neutral solution, one that is neither acidic nor alkaline has a pH of 7.
Water is an example of a neutral solution.
There is a thin film of moisture normally present on the hair follicles and scalp. When measured electromagnetically, the moisture is found to be mildly acidic, with a pH between 4.5 and 5.5. This protective film of moisture is called the acid mantle of the hair. This natural moisture gives hair roots and the scalp its slightly acidic nature, which helps the hair shaft maintain its resliancy, strength and outer coat. Soaps are much more alkaline than shampoos, with pH 10 or 11, which is why they should not be used on hair.