What does a cross-section of a hair strand reveal?

A cross-section of a hair strand provides a horizontal view that allows for an examination of its internal structure, including components such as the cortex, cuticle, and medulla. This structural insight is essential for understanding the hair's properties, such as strength, texture, and potential chemical treatment reactions. By analyzing the cross-section, one can gain valuable information about the condition and characteristics of the hair, which is critical in hair care and treatment practices.

The other options, while related to hair, do not accurately describe what a cross-section reveals. The length of the hair shaft pertains to its linear measurement rather than its internal makeup. The density of the hair relates to how closely individual hair strands are packed in a given area but does not come from a cross-sectional view. The growth rate of hair is influenced by biological factors and is not discerned directly from a cross-section of a strand.