The Science of Hair

Parts of Hair

While you may only think about the hair that you see on your head, there are actually several parts to your hair, both inside and on top of your head.

Follicle – this is the root of the hair, that is underneath the skin. This is where the hair starts its growth.

Dermal Papilla – cells just under the hair follicle that bring blood and nutrients to the hair follicle as well as regulating hair growth.
Hair bulb – the rounded portion of the bottom of the follicle.
Blood vessels – nourish the scalp and hair, bringing key needed nutrients directly to where they are needed for growth.
Scalp – the skin on the top of the head.
Hair shaft – this is the part of the hair that that grows out of the head.
The hair shaft is made up of three layers:

• Cuticle – the outermost protective layer of hair
• Cortex – the main part of the hair, made up of keratin 
• Medulla – innermost layer of the hair shaft, found mainly in thicker hairs

There are two types of hair:

• Vellus hair – thin, fine hair that grows all over the body, usually lighter and shorter than terminal hair
• Terminal hair – these are the thicker hairs that are pigmented, such as the hair on our head

Hair Growth Cycle

Hair grows from the follicle, or root, underneath the skin. The hair is ‘fed’ by blood vessels at the base of the follicle, which give it the nourishment it needs to grow. Between starting to grow and falling out years later, each hair passes through four stages: anagen, catagen, telogen and exogen. At any given time, each hair is at a different stage of the hair growth cycle.

Over time, the length of the anagen stage decreases, making the hair weaker and thinning after each hair growth cycle. That’s why it’s important to ensure your diet is rich in key nutrients to maintain hair health.

Four Phases of Hair Growth: 

1. Growth phase (Anagen)– this is the longest phase of the hair cycle, lasting several years. In this phase, the hair is growing from the follicle.
2. Regression phase (Catagen) – the follicle starts to slow down growth and stops getting nourishment from the bloodstream. This phase can last a few weeks.
3. Resting phase (Telogen)– growth of the follicle has stopped. This phase can last from three months to a year.
4. Shedding phase (Exogen) – this stage is when the hair falls out, and the next cycle begins.

Now that you understand hair growth, let’s learn about hair loss. 

Everyone loses some hair every day. These are the hairs that are naturally in the shedding (final) phase of the hair cycle. It is said that is normal to lose 50-100 hairs every day. Hair loss above this baseline amount can be caused by numerous factors.