Shampoo is slightly acidic to neutral depending on the brand, with levels that range from 4.8 to 7 on the pH scale. Hair conditioner tends to be even more acidic, with pH levels ranging from 2.8 to 7.
The pH (or potential/power of hydrogen scale) is the measure of how acidic or basic a substance is. The scale ranges from 0 to 14, with 7 being neutral. Acidic substances do not attract as much hydrogen, so they are less than 7 on the pH scale. Basic substances attract more hydrogen, so they are greater than 7 on the pH scale. Human hair and skin tends to be naturally acidic, with a pH of 4.5 to 5.5.