The appendage that projects from the epidermis is known as the hair shaft. The hair shaft is comprised of three layers: the cuticle, cortex, and medulla.
The cuticle is the hair’s outer most layer which has shingle or scale like cells that overlap. These cells work defensively to prevent damage to the hair’s inner structure and to control water content of hair fiber. The middle structure includes the cortex which provides strength, color and texture of the hair. The innermost structure is the medulla layer which is only present in large thick hairs. The shingle like cells of the cuticle layer point toward the ends of the hair and are raised during chemical processes. When the cells are raised, solutions are able to enter into the cortex layer.
The improper use of tools, heat, excessive manipulation and chemical over-processing can cause damage to the cuticle layer of the hair, weakening the integrity of the hair. To prevent hair damage, take a proactive approach to healthy hair care by scheduling an appointment with a licensed stylist.
The middle layer of the hair is known as the cortex, and it has many different functions. Approximately 90 percent of hair’s total weight lies within the cortex layer. Elongated cells form a fibrous substance that gives strength and elasticity to the hair. The cortex also houses the pigment (melanin) that gives hair its natural color. Services such as chemical hair relaxing, thermal styling, wet setting and hair coloring oxidation cause temporary and permanent changes to the hair. These changes take place in the cortex layer.
There are two types of melanin that can be found in the cortex layer of the hair: eumelanin and pheomelanin. Eumelanin produces brown and black color, and is the most prevalent type of melanin. Pheomelanin imparts yellow, blonde, red and auburn hues. Natural hair color derives from a peomelanin and eumelanin ratio combined with the size and number of pigment granules. When hair is gray, there is an absence of melanin pigment in the cortex layer.
The medulla, also referred to as the pith or marrow of the hair, is the innermost layer. Composed of round cells, this layer is normally found in thick and/or coarse hair. Naturally blonde and fine hair generally does not have a medulla. The function of this layer of hair does not affect the hair care services conducted by salon professionals.
Beneath the epidermis is a factory of structures working together to promote hair growth. The hair root, the portion of hair underneath the scalp’s surface, works with the dermal papilla, hair bulb, arrectorpili, sebaceous or oil gland and follicle in the formation of hair.
The dermal papilla contains the blood supply and nerves that produce nutrients for the hair. These vital nutrients are needed in order for hair to grow. The dermal papilla is shaped similar to a cone and sits inside the hair bulb.
The hair bulb is another important factory producer. It is located at the base of the hair strand, and its shape is like a club. It acts as a cover for the dermal papilla.
The arrectorpili is a familiar hair factory worker. Its colloquial name is goose bumps. This small muscle fiber lives in the bottom of the hair follicle. Changes in temperatures and fear often cause the muscle fiber to contract, making hair stand straight up. The results, goose bumps, last a few seconds.
The oil glands of the skin are called sebaceous glands. These glands are connected to the hair follicle and secrete sebum, an oily substance that lubricates the hair.