The Structure of the Hair
The Hair follicle is an opening in the skin from which the hair grows. It has a supply of blood vessels; the blood passing though these vessels will nourish the hair.
The hair bulb is situated inside at the base of the follicle, it is from this bulb that the hair shaft is developed.
The dermal papilla, inside the bulb, is the site of production and maintenance of hair growth. Further layers, including the inner and outer root sheath and matrix as shown above, surround the papilla.
The cells continue to produce in the matrix of the follicle, layers develop as a result of continuous cell division, to form the inner and outer root sheath then, ultimately the hair shaft. Together these structures comprise The outer root sheath and The inner root sheath, which contains The Henle layer, Huxley layer, and the cuticle of the inner root sheath.
The emerging hair comprises of layers which are known as the hair cuticle, the hair cortex and the medulla. The
portion of hair above the skins surface is termed the hair shaft. Although this is generally composed of three layers Which are the cuticle, cortex, and medulla. However, the medulla may not be present in all hairs, especially finer ones. The medulla is a layer of loosely connected cells in the centre of the hair. The larger spaces in this layer can influence colour and sheen of the hair.
As the process moves up to the mid follicle region, the dividing cells form a hard protein known as keratin, the formation of these hardening of cells is termed keratinisation. This is the part which is referred to as the hair shaft. Cells in the hair bulb produce colour pigment known as melanin, these cells are termed melanocytes, and these cells are carried into the cortex of the hair shaft.
Typical Hair Growth
The main part of a hair is actually dead tissue. However, the bulb of the hair is considerd as a living tissue, and the hair itself can be an insightful indicator of health.
Hair loss and damage can reveal influences, on the body from such instances as systemic disease, dietary changes, hormonal imbalances, skin conditions, genetic impact, medication, and lifestyle issues.
Hair growth begins at the hair bulb within the hair follicle found in the dermis, (the innermost layer of the skin) beneath the epidermis, (the outermost layer of skin). By the time, the hair has emerged from the follicle, the process of cell division and keratinisation is already complete. Therefore, the visible hair is considered as dead tissue.
Hair growth follows a typical cycle.
- Firstly Anagen - a period of growth that can last from two years to seven years. The hair is firmly anchored in place during this phase
- This is followed by Catagen - a transition phase lasting a few days, in the course of which cell division slows down and then ceases. The hair will become detached from its anchor during this phase.
- Finally, there is Telogen - a resting phase that lasts for approximately 100 days. The hair is now fully detached and can be easily removed.
- Following Telogen a new hair in Anagen will push out the resting telogen hair. This gives rise to normal shedding and a typical healthy person may lose about 30-50 hairs per day, with widespread variation between individuals.
Hair and its growth are nourished by the blood and are greatly influenced by the composition of the blood in terms of nutrients, hormones, and therapeutic drugs. (See Hair Nutrition)
Hair growth in other areas of the body differs in a number of ways.
- Anagen is relatively short, and Telogen relatively long therefore body hair grows only to a short length.
- Principally body hair - with the exception of pubic and axillary hair- is not hormone influenced.