Which part of the hair is responsible for its strength?

The cortex is the part of the hair responsible for its strength. It is the thickest layer of the hair shaft, located between the outer cuticle and the inner medulla. The cortex contains a high concentration of keratin fibers, which provide the hair with its tensile strength and elasticity. This structural integrity is vital for withstanding various physical stresses, such as brushing and styling.

The other components of hair have different roles. The cuticle serves as a protective outer layer, helping to shield the inner layers from damage and moisture loss. However, it does not contribute to the hair's strength. The medulla, which is the innermost layer, is often absent in finer hair and doesn’t play a significant role in the overall strength of the hair. The follicle, on the other hand, is the structure from which hair grows but does not have a direct influence on the strength of the hair itself. It provides nourishment and support during the hair growth cycle rather than contributing to the strength of the hair strands.