The Structure of Hair

Hair Layers

The structure of hair is made up of three layers:

• Cuticle - The outer layer
• Cortex - The middle layer or core
• Medulla - The inner layer

Properties of Hair

There are two physical properties of hair: Elasticity and Porosity. I'm sure you have heard of both of these at one time or another. I'm going to explain why they are important to the health and eventually length of your hair.

Elasticity

Elasticityrefers to the stretching of hair. It is shape, volume, and length based on force. Hair naturally stretches up to 30% when it is wet. In this case, water is the force that lengthens the hair as well as changes the shape and volume. As it dries, it goes back to its original length, shape, and volume. If you have curly hair, the change from wet hair to dry hair can be quite dramatic!

Over-stretching hair can lead to damage. Additionally, perming, coloring, and sunlight can all reduce your hair's elasticity. However, the thicker your hair is, the more resistant it is to stretching.

Porosity

Porosity is how much water can get in and out of the cortex of the hair. With normal, healthy hair, very little water can get in or out. This means that the cuticle is intact and acts as a shield to the cortex.

Overporous hair happens when chemicals enter the cortex and react with the protein keratin. Blow-drying, flat irons, curling irons, wind, and sun can all lead to over porous hair. This is due to the cuticle becoming fragile and allowing water to get in and out of the cortex eventually leading to dryness and split ends.