Studies have shown that the pH of hair has a great effect on it’s resilience. The pH is measured from 1 to 14, with solutions closer to 1 being more acidic and solutions closer to 14 being more basic. Water is neutral at a pH of 7.
When hair is immersed in a solution between a pH of 4.5-6 the hair is less likely to break and has more stretch. When placed in extremely acidic or basic solutions, the hair has an increased likelihood of breaking.
The more basic the solution, the more the cuticle scales will swell and open leading to the abovementioned problems. The hair can soften and stretch thinner to the point of breaking.
With acidic solutions, the cuticle lays flat and allows for better light reflection which leads to the appearance of shinier hair. A flat cuticle also allows better slippage between individual hairs which helps reduce breakage. However, if the hair is too acidic, the cuticle scales shrink, harden, and the hair fiber will break when bent.
Chemists talk about solutions that are acidic and alkaline. This has been the basis of hair product formulation.