What is the role of the medulla in hair?

The medulla serves as the innermost layer of the hair shaft. In terms of structure, it is positioned at the center, surrounded by the cortex and cuticle. This layer is particularly significant because it can vary in presence; it is often absent in fine or very thin hair strands, while coarser hair types typically contain it.

The presence or absence of the medulla can influence other characteristics of the hair, such as its overall strength and texture. Thus, understanding the role of the medulla is crucial for cosmetologists, especially when considering hair types and their unique properties.

The other options represent different functions or components related to hair structure. The outer protective layer refers to the cuticle, which safeguards the inner structures. Moisture retention primarily involves the hair's cortex and external treatments rather than the medulla. Temperature regulation is not a function of the hair itself but rather pertains to the scalp and body thermoregulation in general.