Ace the California Cosmetology Exam 2026 – Style Your Way to Success!

The cortex is the part of the hair primarily responsible for its strength. It is the thickest layer, located between the cuticle (the outer layer) and the medulla (the innermost layer). The cortex contains fibrous proteins and is rich in melanin, which contributes to the hair's color and overall structural integrity.

The fibers in the cortex provide tensile strength, allowing hair to resist breaking and to withstand various treatments and environmental factors. Moreover, the cortex's unique structure can absorb moisture and helps maintain the hair's suppleness and flexibility. Therefore, the strength of hair largely depends on the condition and health of the cortex.

The other parts, while important in their own right, do not play the key role in hair strength that the cortex does. The cuticle protects the inner layers but does not contribute significantly to strength. The medulla's function is less understood and varies among individuals; it does not directly contribute to the hair's overall strength. The hair shaft is the visible part of the hair and comprises all three layers, but it does not uniquely determine strength relative to the cortex.