“pH” is an abbreviation for “potential hydrogen” and is a scale used for ranking the relative acidity or alkalinity of a liquid solution. The precise mathematical definition of pH is the negative logarithmic value of hydrogen ion (H+) concentration in the solution. pH = – log [H+]
A scale of zero to fourteen is used for pH, with 7.0 being a neutral solution (water). A number below 7.0 is considered to be acidic, with a lower number being more acidic, and anything above 7.0 is considered to be alkaline or basic, with 14 being the strongest alkaline value. Due to the logarithmic nature of the pH scale, a solution with a pH of 2.0 is ten times more acidic than one with a pH of 3.0. Human hair is a solid material, a composite of protein molecules with three distinct layers. The central portion called the medulla is not present in every hair and is usually just made up of air. The surrounding layer, known as the cortex, is composed of bundles of fibrous coils made of keratin protein molecules that supply the hair strand with its strength and elasticity. The cortex also contains particles of melanin, which impart color to the hair strand. The outer layer is comprised of multiple layers of overlapping, keratinized scales and is called the cuticle, which acts to protect the cortex and medulla. Hair and skin are both covered by a very thin fluid layer comprised of oil, salt and water, called the mantle, which is slightly acidic (pH = 4.5 – 5.0). This acid mantle is very important in maintaining the proper moisture balance in our hair and skin. It is also instrumental in making the cuticle scales lie flatter against the surface of the hair shaft, which makes hair smoother and shinier as the flat scales reflect light more coherently. Scales that lie more snugly against the hair shaft also prevent moisture loss more efficiently, which helps hair to be stronger and healthier. With the normal exposure to the environment as well as washing and styling, this acid mantle can become contaminated or removed and must be restored with the use of properly pH-balanced products.