In hair care, what contributes most significantly to the overall strength of hair?

The cortex is the middle layer of the hair shaft and plays a crucial role in determining the overall strength and elasticity of hair. This layer is composed of long chains of keratin proteins, which provide structural integrity. The cortex also contains most of the hair's pigment, contributing to its color and influencing its strength. Because of its dense, fibrous nature, the cortex absorbs moisture and buffers against environmental stressors, enabling the hair to withstand daily wear and tear.

While the cuticle layer, which is the outermost layer, provides some level of protection, it is comparatively thin and primarily serves as a shield against environmental damage. Natural oils produced by the scalp do help to moisturize and protect the hair but do not provide the structural strength that the cortex does. Environmental factors certainly can affect the condition and appearance of hair but do not inherently contribute to its strength. Thus, understanding the role of the cortex clarifies why it is the primary contributor to hair strength.