Does the acidity of my shampoo make any difference?

Hair is composed largely of keratin, which is protein. Proteins are constructed from amino acids. Keratin is particularly rich in the amino acid, cysteine, each of which contains a sulfur atom. These sulfur atoms on adjacent keratin proteins can bond to one another, thereby making the hair shaft strong and resilient. Alkaline solutions, characterized by a pH greater than 7, can destroy these disulfide bonds. Acidic solutions, which have a pH less than 7, serve to protect these bonds, and consequently, the strength of the hair shaft. Thus, shampoos that are somewhat acidic are good for the health of one's hair and can even help moderate potentially damaging exposure to alkaline solutions.