What is the main role of the hair cortex?

The main role of the hair cortex is to give hair its strength and elasticity. This inner layer of the hair shaft is composed of long chains of proteins that contribute to the overall structural integrity of the hair. The cortex accounts for about 90% of the hair’s weight and contains melanin, which provides color. The strength provided by the cortex is crucial because it allows hair to withstand various physical stresses, such as styling and environmental factors, without breaking. Elasticity, which refers to the hair's ability to stretch and return to its original shape without damage, is also primarily determined by the condition of the cortex.

While the protective outer layer of hair, known as the cuticle, does help shield the inner structures from damage and can contribute to shine, it's the cortex that plays the pivotal role in the essential characteristics of strength and flexibility that are vital for healthy hair.