Which hair structure is considered the innermost layer?

The innermost layer of the hair structure is known as the medulla. This cylindrical core is found at the center of the hair shaft and is composed of loosely arranged, unorganized cells that may contain air spaces. The medulla is often present in coarser hair types but may be absent in finer hair.

In contrast, the cortex is the middle layer of the hair shaft and is responsible for the strength, color, and texture of the hair. It contains tightly packed cells and the majority of the hair's pigment is located within this layer. The cuticle is the outermost layer, formed by overlapping scales that protect the inner layers of the hair from damage and environmental factors.

The dermis is not part of the hair structure itself; rather, it is a layer of skin that houses hair follicles, among other structures. Understanding these distinctions is crucial in cosmetology, as they relate to hair health, treatment, and care.