Hair is an important part of the body’s structure. It is made up of a tough protein called keratin. It grows in the same way as other tissues, from a stocking-like structure underneath the skin known as a hair follicle. Blood vessels nourish the cells in the follicle and deliver hormones that modify hair growth and structure at different times of life.
The cells in a hair follicle divide rapidly and push the stem of the root upward to form the shaft of the hair. As the stem moves up, it is cut off from nourishment and begins to develop a hard, protein-filled substance known as keratin. As the keratin grows, it becomes filled with dead cells that die and are replaced by new cells.
When the keratin has grown to its full length, the hair shaft is formed. It has two or three layers: The Inner Layer – Medulla
This innermost layer of hair contains the keratin that makes it supple, smooth, and strong. It also has pigmenting cells responsible for giving hair its color.
Its surface is covered by a protective layer of squamous cells, called the cuticle. This layer protects the keratin and melanin from damage caused by friction, sunlight, or chemicals.
When a strand of hair reaches the surface of the skin, it begins to form an outer layer of cells called the epidermis. This outer layer contains sweat glands that produce and secrete the oils needed for healthy hair.
These oils help moisturize the skin and trap tiny particles like dust and dirt around the eyes and ears, so the body’s immune system can fight infection. It also helps the body maintain a consistent temperature.
Most hair is still growing when it reaches the surface of the skin; however, it can also be shed, or “molted.” The amount of hair that grows at any given time varies. This is because the hair follicle cycles between anagen (growth phase) and catagen (transitional phase).
Human hairs are unique in that they have microscopic characteristics arranged in patterns and distributed throughout their various regions that permit a skilled examiner to distinguish them from one another. These differences allow hairs to be identified in a variety of situations and are especially useful when examining hair samples taken from victims of crime or other types of investigations.
The morphology of human hairs can also serve as an indicator of group membership or other social roles in which the hair is displayed. For example, hairstyles that are short on top and trimmed to a particular length may signal group membership in a society or organization. This type of identification is sometimes referred to as a “haircut.”
The age of an individual can also be determined by the microscopic appearance of hairs. This can help investigators identify certain individuals, such as infants or elderly people, who are more likely to have finer and less distinctive hairs.