Men and women of all races have the same hair structure. All human hair consists of three main layers. The Cuticle, the Cortex, and the Medulla.
The outer layer of the hair is called the cuticle. It is made of long, molecular chains of amino acids (protein) and is the largest section of your hair.
It is designed to protect the inner layers of the hair shaft. The appearance of the hair’s cuticles has been compared to shingles on a roof or scales on a fish. In healthy hair, the cuticle scales lay flat. In damaged hair, the scales may be missing or broken. Cuticles that lay flat against the hair shaft do the best job of providing protection. Cuticles are often damaged by excessive mechanical manipulation such as brushing and/or using heat or chemical processing. Additionally every day elements, such as the sun or wind can cause wear and tear on a person’s hair and damage the cuticles as well. The cuticle layer is your hair’s armor; it protects the heart, or the cortex, the layer beneath the cuticle.
The second layer of hair is called the cortex, which is made up of long proteins that twist like a curly telephone cord. This is also the part of your hair that’s most responsible for its overall strength, elasticity, and color. Hair that’s dry and brittle does not hold good moisture content in its cortex. As a result, it will not be elastic enough to withstand the rigors of mechanical and chemical manipulation and will break very easily.
When you get split ends, or damage in midshaft, you’re seeing your cortex at its worse. The protective cuticle has been worn away and is now exposing your cortex. Once your cortex is exposed, the hair is damaged beyond repair. Since hair isn’t living tissue, it doesn’t have the healing properties that your skin does, hence, it cannot regenerate itself. Damaged hair can be patched up at best using various products, however, it can never be fixed. Damaged hair will either break on its own, or in the case of split ends will have to be trimmed.
The innermost or center portion of the hair shaft is called the medulla. It is composed of round cells, two to five rows across. Thick or coarse hair usually contains a medulla. Fine hair for the most part lacks a medulla, as does naturally blond hair. The purpose of the medulla has not yet been determined.