Although shampoos vary in acidity and alkalinity, most shampoos range from 5 to 7 on the pH scale. The best shampoos are those that are slightly acidic to neutral. The higher the pH number, the harsher the shampoo on a person's hair.
The pH scale measures the acidity or alkalinity of a substance. The scale starts at 0 and increases to 14. The lower end of the scale is acidic and the high end is alkaline. Neutral pH is indicated by 7.
Different shampoos have different pH numbers. The best ones are those that are in the neutral or near-neutral range of the scale. Consumers should avoid shampoos with a high pH as those are more alkaline and tend to be too harsh for healthy hair care.
The specific type of shampoo varies depending on one's hair type and condition. For example, hair that has been color treated tends to be extremely dry. To compensate for this, the scalp naturally produces more oil. Using a shampoo that is pH-balanced helps keep the amount of oil in check and keeps hair looking healthy and clean rather than oily and dirty.
The pH number is not often indicated on the label of the shampoo. As a general rule of thumb, however, baby shampoos tend to run at a pH of 7 while daily adult shampoos average 5.5.