Your hair consists of two or three layers: the cortex, medulla, and cuticle. The cuticle is the outermost layer, and it is composed of flattened cells that overlap like the tiles on a terra-cotta roof. It helps to protect the hair shaft from damage and adds shine.
The follicles that give rise to straight hair are oval-shaped and the follicles that produce curly hair are curved, with a primary c-shaped curve at the top and a secondary curve at the bottom. Both hair types serve many purposes. For instance, hair in the nose protects the ears from dust, and the hair around the eyes helps to prevent sweat and particles from getting into the eyes. The eyebrows are also important, as they serve as sensory input.
The cortex of your hair consists of long proteins. The cortex resembles a curly telephone cord. It is elastic, and stretching it straightens out the coiled proteins in the cortex. The cortex also contains pigments that give hair its color, which are tucked into the strands and protected by the translucent cuticle cells.
Researchers believe that hair has its origins in the common ancestor of mammals. This ancestor was a synapsid, but fossils of synapsids rarely provide evidence for soft tissues, such as hair. In contrast, the basal synapsid stock bore transverse rows of rectangular scutes, a feature similar to that of modern crocodiles. This means that hair could not have originated earlier than 299 million years ago.
Hair is a biomaterial composed of keratin and other proteins that make up a filament that covers the human body. It protects the human body from external factors and influences social and sexual interactions. Despite its ubiquity, hair has many uses and is a valuable biomaterial. Its functions include producing sebum, apocrine sweat, and pheromones.
A hair follicle contains three layers of cells. The inner root sheath (IRS) is the innermost layer and is made of cuticle cells. These cells interlock with the hair cuticle and anchor the hair shaft to the hair follicle. The outer root sheath is a layer of cuboidal cells that resembles the epidermis at the infundibulum. This layer is keratinized and becomes multilayered in the upper portion of the hair bulb.