We spend a lot of time worrying about the style, colour and texture of our hair, but how many of us actually know what hair is? By learning about the structure, components and growth cycles of hair we can start to understand more about what our hair needs to be truly healthy.
So what is hair?
Hair is made up of the protein Keratin. This is a compound containing Carbon, Hydrogen, Oxygen, Nitrogen and Sulphur. There are three types of hairs found on the human body; Vellus hair which is fine and colourless, Intermediate hair that responds to hormones and grows on the pubus and axillary regions, and Terminal hair which is found mainly on the scalp (and will be our focus in this article).
Terminal hairs are themselves composed of three concentric layers:
- The Medulla – the innermost layer of the hair.
- The Cortex – the thickest portion of the hair composed of flat cells containing hard keration and melanocytes.
- The Cuticle – this is a single layer of flattened cells, and has the appearance of scales.
The granular pigments you can see in this diagram are the mix of blue, red and orange pigment that are naturally found in the hair. This determines the colour of your hair, and broadly varies with nationality and race. This is also the pigment that is altered when your hair is coloured. The outer cuticle layer itself has no colour, and without any pigment inside the hair appears white.
How does hair grow?
Hair grows from an indentation in the skin called the papilla which is nourished by a rich blood supply. As the hair grows through the different layers of skin it is protected by the follicle sheath, and lubricated along the way by oil from the sebaceous gland. This oil is called sebum and protects both the scalp and hair – this is the substance that can cause hair to look ‘greasy’.
There are three phases in the life cycle of a hair:
Anagen – this is the active period of growth. A scalp hair will actively grow for between 1.5 – 7 years, and the average rate of growth is 1.25cm per month. The growth slows down as the hair ages. By a length of 25-30cm the rate of growth slows drastically to little over half it’s previous rate. Hair rarely grows longer than 100cm.
Catagen – this is the end of the active growth period (anagen) and when changes begin to happen in the follicle. The hair stops growing and becomes detached from the base of the follicle. The hair bulb begins to break down resulting in the follicle becoming shorter. A small section of the root remains in contact with the papilla to form a new hair. This period of the hair breaking down takes about 2 weeks.
Telogen – this is the resting stage. The shortened follicle rests for 3-4 months before being ready to grow a new hair. At any one time approximately 13% of the hair is in this resting period. If all the hair entered this stage at once then the hair would moult, as with animals. In humans the follicles are at different stages of growth so there is constant shedding of about 100 hairs a day.
To keep hair as healthy as possible we therefore need to consider the health of both the hair itself (keeping the shaft hydrated and the cuticle smooth and conditioned) and the scalp (not stripping it of all its natural oils, or clogging the follicles with product build-up).