Here’s a quick science lesson in hair – we promise it’s interesting and will help you understand your hair more!
Hair is a filament made mostly from protein (keratin) and is produced in the follicle. The follicles are found in the dermis (2-5mm into the skin).
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.
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Hair contains 3 layers:
The cuticle is the outermost layer, consisting of scale-like overlapping cells formed from dead cells. They give the hair shaft strength.
The cuticle can be damaged by excessive heat (straightening irons etc) and by chemical damage (like bleach). Environmental factors like the sun and wind, plus excessive brushing and harsh handling will also damage the cuticle.
The cortex is the fibrous middle layer of hair. This consists 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 (melaline) that gives hair its colour.
The medulla is the most inner layer of the hair structure, consisting of sparse cells and air bubbles. Its role in humans is unknown, however in animals it helps to control body temperature.
The 3 Stage Hair Growth Cycle:
There are three stages to the growth cycle of hair. The entire cycle can be as short as 1 year or as long as 7 years, with the average growth cycle being 4 years.
Because we’re all individual, our growth cycles will differ from person to person. However, many factors can also interrupt the cycle and induce hair into the Telogen (hair shedding) stage. It is understood that the protein FGF-5 triggers the hair to change from Anagen to Catagen and then to shed.
The Anagen Phase: (growing phase – lasts 1 to 7 years)
- 80-90% of hair is in the Anagen phase
- Hair growth is approximtely 1.25 cm a month however can vary from person to person
- The hair bulb produces melanine (the hair colour pigment) in the growth cycle
- The blood supply provides nutrients and minerals to the hair
The Catagen Phase: (transition phase – lasts 1 to 3 weeks)
- 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 up towards the surface when the new hair is formed
- Approximately, 2-3 % of hair is in this phase
The Telogan Phase: (resting phase – lasts up to 3 months)
- 10-15 % of hair is in Telogen phase
- Up to 100 hairs a day can be shed in a normal Telogen phase – don’t freak out, this is normal!