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.
Hair fibers are composed of many layers with the three most commonly discussed layers being the medulla, the cortex, and the cuticle.
The central medulla is the only living layer of the hair fiber and contributes to the thickness of each hair fiber. The medulla does not extend the entire length of the hair fiber and with age, shortens and thins, leading to fine hairs.
The cortex is the middle layer composed of keratins and melanin and maintains the integrity of the hair fiber from root to tip. The cuticle contains melanin, a pigment that gives hair it’s color. A separate article describes how melanin can make hair colors from blonde to red to black. The cortex is what holds the negative charge of hair and allows the cuticle to adhere. The cortex is important for maintaining the moisture content of the hair fiber.
The cuticle, commonly targeted by hair products, is the outermost layer of the hair fiber. Under high magnification the scales of the cuticle resembles overlapping shingles on a roof. This layer is susceptible to everyday elements such as heat, sun, and chemicals. These added injuries cause mechanical damage and can alter the pH of the hair. These changes can alter the cuticle causing the individual scales to swell, soften, and open. This allows increased friction which complicates the hair fibers with tangling, knotting, reduced slip of the hair, and increased breakage.
Image of cuticle: Healthy on the left and Damaged on the right.