Hair is a filament made mostly from protein (keratin) and is produced in the follicle. These follicles are made up of a papilla, matrix, stem cells and sebaceous gland, all of which are required for hair growth. The thick, long hair found on our heads is called terminal hair and the fine, short hair on the rest of the body is called velus hair. Hair contains 3 layers:
The cuticle – The outermost layer consisting of scale-like overlapping cells five to twelve deep. It is formed from dead cells and gives the hair shaft strength and provides protection for the softer inner structures. The cuticle can be damaged by excessive use of heat such as straightening irons, and by chemical damage (colouring etc). Everyday elements, such as the sun or wind, brushing and harsh handling will also damage the cuticle.
The cortex – The fibrous middle layer of hair consisting of keratin filled, elongated cells that are cemented together with lipid rich, flexible keratin. This gives the cortex the properties of elasticity and a high tensile strength. The cortex contains the pigment (melanin) that gives hair its colour.
The medulla – The inner most layer of the hair structure consisting of sparse cells and air bubbles. It’s role in humans is unknown, however in animals it helps to control body temperature.
The Hair Growth Cycles – There are three stages in the hair growth cycle. The entire cycle can be as short as one year or as long as seven years with the average growth cycle being four years. As we are all different our growth cycles will also differ. Many factors can interrupt the cycle and force the hair into the Telogen stage (hair shedding). It is understood that the protein fgf-5 triggers the hair to change from Anagen to Catagen and then to Telogen
The Anagen Phase: Lasts 1-7 years – Growing phase
- 80-90% of hair is in the Anagen phase
- Hair growth is approximately 1.25 cm a month however can vary from person to person
- The hair bulb produces the hair colour pigment, melanin in the growth cycle
- The blood supply provides nutrients and minerals to the hair
The Catagen Phase: Lasts 1-3 weeks – Transition phase
- The hair detaches from the blood supply
- The detached follicle will slowly shrink to about 1/6 of its size
- The hair bulb stops producing the colour pigment
- The bulb will be pushed upwards towards the surface when the new hair is formed
- Approximately 2-3 % of the hair is in this phase
The Telogen Phase: Lasts up to 3 months – Resting phase
- 10-15 % of hair is in Telogen phase
- Up to 100 hairs a day can be shed in a normal Telogen phase.