Hair Structure and Hair Life Cycle
Hair is composed of strong structural protein called keratin. This is the same kind of protein that makes up the nails and the outer layer of skin.
Each strand of hair consists of three layers.
- An innermost layer or medulla which is only present in large thick hairs.
- The middle layer known as the cortex. The cortex provides strength and both the color and the texture of hair.
- The outermost layer is known as the cuticle. The cuticle is thin and colorless and serves as a protector of the cortex.
Structure of the hair root
Below the surface of the skin is the hair root, which is enclosed within a hair follicle. At the base of the hair follicle is the dermal papilla. The dermal papilla is fed by the bloodstream which carries nourishment to produce new hair. The dermal papilla is a structure very important to hairgrowth because it contains receptors for male hormones and androgens. Androgens regulate hairgrowth and in our scalp hair, Androgens may cause the hair follicle to get progressively smaller. This leads the hairs to become finer in individuals who are genetically predisposed to this type of hair loss.
Simply, each strand has three phases of hair growth. Each strand on your head is at its own development stage. When this cycle is complete, a new strand will grow in its’ place and the process starts all over again. Thankfully, you’ll never get all the strands on your head reaching its’ terminal growth at the same time or all your hair will shed simultaneously, leaving you bald (cue the hat/wig/balaclava – or a smile for the brave ones).
I’ll break down each stage of hair growth for you:
- Anagen: Growth Phase – Each strand on your head has its own individual rate of monthly growth for a time period (on average two to six years at a time). To a certain extent, the rate your strands grow and how long this lasts is dependable on your genes but your environment and how you personally look after your hair are also highly influential. So, the longer your hair stays in this phase, obviously the longer it will grow.
Here’s a fact for you – at any given time, around 85% of hair on our head is in this phase.
- Catagen: (or transitional phase) This period lasts approximately two weeks. Your hair follicle shrinks by a sixth and the dermal papilla ‘takes a breather’ by cutting your strand off from its’ nourishing blood supply.
- Telogen: (or resting phase) During this final stage lasting between one to four months, the hair doesn’t grow but remains attached to the follicle while the dermal papilla stays dormant. The papilla and bottom of the follicle reconnect and a new hair now reforms. The old hair strand is pushed out by your new strand, which is what causes the natural process of shedding.