What is the innermost layer of hair called?

The innermost layer of hair is called the medulla. This central core of the hair shaft is often composed of loose cells and air spaces, making it less dense than the outer layers. While not all types of hair contain a well-defined medulla, when it is present, it serves as a structural element that can affect the hair's overall strength and insulation properties.

Understanding the roles and characteristics of the hair layers is essential in the field of cosmetology, as it can influence decisions regarding hair treatments and styling. The cortex, which is the middle layer, plays a crucial role in providing hair with its strength and color, while the cuticle, the outermost layer, acts as a protective barrier. The dermal layer, mentioned in one of the choices, refers to the layer of skin beneath the scalp where hair follicles reside, but it is not a part of the hair structure itself.