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The medulla, also known as the hair cuticle, is the innermost part of a strand of hair. It is surrounded by the cortex, which in turn is protected by the outer layer, thecuticle. Together, these three layers form the structure of the hair shaft.
The medulla can be hollow or filled with keratin and is not present in all hair types. Its exact function is not fully understood, but it is thought to contribute to thermal insulation and may play a role in the distribution of nutrients in the hair. The medulla is typically found in thicker hair, such as head hair or beard, and may be absent in finer hair such as that on the arms or legs.
The cortex is the middle layer of the hair shaft and is made up of long keratin fibers that are responsible for the strength, color and texture of the hair. The cortex also holds most of the moisture in the hair and can be chemically treated to color, bleach or reshape the hair.
The cuticle is the outermost layer of the hair shaft and consists of several layers of overlapping scales that protect the hair from damage. The cuticle determines how healthy the hair looks, and its integrity influences the shine and smoothness of the hair. Damaged or worn cuticle layers can lead to dry, brittle and dull hair.
Together, these three layers play an essential role in determining the properties and overall health of the hair. While the medulla may be responsible for the inner structure, the cortex and cuticle contribute significantly to the strength, elasticity and appearance of the hair.
