According to The Natural Haven, the pH of shampoo ranges from 3.5 to 9 based on different non-alkaline brands. The Natural Haven's classifications are based on the manufacturer's stated pH levels and their own tested pH levels.
Most of the shampoos tested are concentrated between 5 to 6 pH levels, indicating low levels of acidity. Only Trader Joe's Nourish Spa was completely pure at pH of 7. In addition, alkaline soap-based shampoos tend to be more basic with pH levels of 10 and above. There are also shampoos that contain solids, which result in unreliable pH values due to their lack of water solubility.