Hair is naturally about ph7. it is damaged if the ph goes below 3 or above 10. what do you think ph balanced shampoos do

Human hair and sebum  has a pH in the range from 4.5 - 5.0. The natural hair is slightly acidity in nature. Acidic nature of hair assist in preventing fungi and bacteria growth in the hair and scalp, as well it leaves the cuticle closed.

Now, if the hair is too basic in nature i.e. pH > 10,  it will cause the hair cuticle to open. On other hand, too acidic hair will cause the cuticle to contract. 

The pH balance shampoo assist in maintaining to pH level to slightly acidic side i.e. ~ 5. This ensures growth of healthy hair. 

Tolerance to high levels of salinity