How does hair grow?

To the question "How does hair grow?" you're probably thinking, "It doesn't!" and believe me, I share your point of view. However, an understanding of how hair is formed and how it grows is crucial to understanding why we lose our hair and how - potentially - we might one day be able to start growing it again.

The first thing to know is that hair, which we've already seen is made from a protein called keratin, grows from a "follicle". A follicle is sometimes described as a pouch or sac and is comprised of various parts - the pear shaped "papilla" at the base, the "hair matrix" which surrounds the papilla and is where cell division takes place (a process which is mainly responsible for creating the hair itself), the "root sheath" and the "hair fiber". A sebaceous gland which produces sebum and tiny muscle fibers called "arrector pili" are attached to the follicle.

So, those are the basic building blocks, how do they work together to produce a growing hair? The crucial thing to realise here is that hair doesn't just grow, it grows in phases, the main phases being anagen, catagen and telogen. Here's a quick rundown of what happens in each of these phases:

Anagen - In this stage the cell division in the follicle mentioned above is taking place rapidly and this causes the hair to grow (about 10cm per year). Hair on the head (and let's face it, that's the area most of us are interested in) remains in this phase for around 2-3 years, occasionally longer - even as much as 6 years. Around 85% of hair is in this phase at any one time.

Catagen - This phase is known as a transitional phase and lasts for around 2 to 3 weeks directly after the anagen phase. The hair follicle shrinks and the lower part is destroyed.

Telogen - The resting phase. The hair does not grow during this period and for head hair this phase lasts about 100 days. 10-15% of hair is in this phase at any one time. When this phase is complete the anagen phase is entered once more and a new hair begins to grow, pushing out the old hair if it has not already been shed. It is normal to lose around 50-100 hairs for this reason each day.

That's it, basically. Simple, isn't it?!