The hair strand is made up of 3 different parts:
Both the cuticle and cortex are found in every hair type, while the medulla is only found in thicker hair types. Each layer of the hair strand serves a different function and is important to the look, feel, and health of your overall hair.
The cuticle is the outermost layer of the hair and is made up of overlapping cells that resemble fish scales, typically 6-10 layers deep. A healthy cuticle is smooth and flat, which makes hair shiny. It also has an incredibly important job—protecting the innermost parts of the hair from damage.
So, what can damage the hair’s cuticle? Chemical processes such as bleach and color treatments, and even environmental factors can cause the cuticle to lift, which leads hair to become dry, brittle, and weak—ultimately resulting in breakage.
The cortex forms the hair’s main thickness and color. It consists of long keratin filaments (hair proteins), which are held together by disulfide and hydrogen bonds.
The health of your cortex depends largely on the health of the cuticle protecting it. An unhealthy hair cortex may make hair feel rough and damaged—which can make hair tangle and knot easily.