Hair is protein fiber which grows from follicles which can be found in the dermis. Hair fibers have a structure which consists of several layers. Outside of the hair is called cuticle which consists of flat and thin cells which overlap one another like fish scales. Then comes cortex which contains keratin and melanin in rod-like cells. The middle of hair is called medulla which is opened and disorganized area at the center of the fiber.
As we can conclude, each hair is made up of these three elements – medulla, cortex and cuticle. In one word innermost region of the hair is medulla, middle layer of the hair is cortex, but the outer layer of the hair is cuticle.
The main bulk of the hair is made of long fibers which are twisted together, reminding the rope. This is the cortex, which is highly structured and organized layer which is responsible for mechanical strength and water uptake of the hair. As mentioned before, cortex contains melanin which colors the fiber, basing on the number, distribution and type of melanin granules, therefore, we can say that the cortex determines the color of the hair. There are two kinds of pigments in the cortex – eumelanin which gives brown and black color, and pheomelanin which gives yellow and red color.
The cuticle, as it mentioned before, is covered by scales, therefore, it can be several layers thick and it is responsible for flexibility of the hair. The cuticle is transparent, allowing the color of the cortex to be seen.
Human head has hundreds of thousands of follicles which are pore-like structures within the scalp. Hair begins to grow inside of the hair follicle by the papilla which is the only living part of the hair – hair which is visible on the skin surface has no biochemical activity, therefore, is it considered as dead. In one word, hair is made up of dead cells. As the new cells grow, older cells die and are forced through follicles towards the scalp. These dead cells are compressed to form a protein which is called keratin. The hair shaft which is seen on the skin is the keratin. It should be mentioned, that each hair consists of keratin, water and binding agent which holds the keratin and the water together.
The base or the bulb in the hair root contains cells which are responsible for producing of hair shaft. Hair follicle also includes sebaceous gland which is responsible for producing of oil which lubricates the hair and surrounding muscles called arrector pili muscles which cause standing up of hair or goosebumps.
Each of hair follicles produces many hairs during human lifetime. Human hair grows, stops growing, falls out and then starts to grow again. Of course, there can be several factors that affect this process of renewal, therefore, the hair does not grow back and causes baldness. Human hair grows for 1 to 7 years, and it can grow from 28 to 36 inches if it is not cut. In general there are three stages of hair growth – anagen, catagen and telogen.
Anagen is the stage which can last for a month or few years. It is the main stage of hair growing where papilla produces most hair cells. Catagen is the stage when the hair stops growing – the bulb of the hair shaft separates from the papilla and shrinks upwards. Telogen stage is known as hair falling stage, because then follicle stops hair growing and rests – the bulb shrinks and detaches from the bottom of the follicle, falling out from the head. It should be mentioned, that during telogen stage a new hair begins the growth phase, pushing the old one out of the follicle.
The shape of the follicle affects the shape of the cortex, but the shape of the fiber affects the straightness or curliness of the hair. For example, people with round hair fibers have straight hair, but people with oval or irregularly shaped fibers have wavy of curly hair.
Generally there are three types of the hair – African Caribbean, Asian and Caucasian (European). African Caribbean hair usually are very tightly curled and often very dark. Asian hair is mostly straight and lank, and it can be thick and strong. Asian hair color can be from medium brown to very dark. Caucasian or, in other words, European hair can be straight, wavy or even curly, and is varies in color from light blond to very dark brown.
Taking about hair texture, hair can be fine, medium or coarse. When we talking about fine, medium or coarse hair, we mean that each hair is like that. The texture of hair is determined, basing on its circumference and cuticle condition, for example, fine hair has smaller circumference than medium and coarse hair. The diameter of human hair varies from 0,017 to 0,18 millimeters. It should be mentioned, that the hair texture can vary greatly depending on hair color and racial type of human.
Hair density depends on the number of hair on the head, therefore, people with fine hair may have more hair on their head than people with coarse hair. Of course, the number of hair on the head depends on several factors, but on average owners of natural blond hair have 130 000 hair, owners of natural brown hair have 100 000 hair, owners of natural black hair have 100 000 hair, but owners of natural red hair have 80 000 hair.