What is Hair Made of? And How Does it Grow?

Like your skin, understanding the different layers of your hair is essential—so you can better care for it, help it grow, and make it as healthy as possible. A common question from Nutrafol customers is: 

“What are the different layers of my hair, and why are they important?”

Your hair is made up of two structures: the hair follicle and the hair shaft. The hair follicle is the point from which your hair grows, while the hair shaft is the hair you see above the skin—the hair we wash, style, brush, and see in the mirror. This is also called the hair strand.

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.

Those who have thicker, fuller hair can thank the medulla. The medulla is the innermost layer of the hair. It consists of a soft, thin core of transparent cells and air spaces. Thinner hair types do not have a medulla layer, resulting in less thickness and finer hair. This does not mean that finer hair can’t be strong and healthy. 

Damaged hair can affect our ability to grow thicker, stronger, longer hair. It’s important to support your hair with the right scalp care products, an outlet for physical and emotional stress, and a daily hair routine that fits your lifestyle.