The hair anatomy is the first topic apprentice hairdressers learn to start their career and I’m sure a lot of hair enthusiasts wonder why our hair allows us to change it into so many shapes when styling hair?
What is the function of hair on the scalp?
The main function of your beautiful locks of hair on your scalp is to protect the skull area from sun exposure.
While your hair is being your warrior by protecting your scalp, it can burn and become damaged from the UVA and UVB rays from the sun. The damage from the sun can also cause hair lightening, dullness, split ends and breakage in the long-term. This is why it is great to thank your hair for its protection of your scalp by nourishing it with sun protection sprays and after sun care treatments.
Not only does your hair protect you from the damaging effects of the sun, it also acts a heat insulation to keep the body warm. Alternatively when you’ve done a hard workout at the gym and sweated out all those toxins, the sweat is evaporated from your drenched hair and aids in cooling the body down.
And as we all know our hair plays an important role in our social environment. The texture, colour and way we style our hair attracts attention from others.
From the sleek pony that can come across in the workplace as ‘I mean business’ or sexy volumes waves for your hot date.
So I guess we can say our hair is our own personal hero.
When are the hair follicles formed?
All of the bodies hair follicles are formed by week 22, of a developing foetus.
Each person will have between 80,000 to 150,000 hair follicles on the scalp.
No new hair follicles are generated during the course of our lives.
Our scalps expand as we grow and during this process most people will notice the density of their scalp hair reduces because of this.
What is a hair follicle?
The hair follicle is the skin organ in the fat of the scalp that contains cells and connective tissues that produces hair. The structure contains several layers and each has separate functions:
Papilla - contains capillaries or tiny blood vessels that nourish the cells and is found at the base of the follicle.
Blub - is surrounding the papilla at the very bottom of the hair follicle. The cells of the bulb divide every 23 to 72 hours. It contains hormones that affect hair growth and structure during different stages of life.
Inner and outer sheath – are structures that protect and form the growing hair shaft.
Sebaceous gland - is vital because it produces sebum, which conditions the hair and skin.
Erector pili muscle - When this muscle contracts, it causes the hair to stand up which also causes the sebaceous gland to secrete oil. This action is better known as ‘goose bumps’ on our arms and legs.
What are the layers of a hair stand?
The hair shaft is made up of three layers of keratin, a hardening protein. Here are more details about those three layers.
Medulla (The Innermost Layer) - This nearly invisible layer is the most soft and fragile part of the hair. Depending on the type of hair, the medulla isn't always present.
Cortex (The Middle Layer) - Is the thickest hair layer. It contains most of the hair's pigmenting cells that are responsible for giving hair colour. The pigment in the cortex is melanin, which is also found in skin.
Cuticle (The Outer Layer) - Is formed from dead cells, overlapping in layers, which form scales that strengthen and protect the hair shaft against physical and chemical injuries.It helps aid in the removal of dirt and old cells from the scalp.
What is hair made out of?
Keratin - Hair comes in many different colours and textures but it’s all made of the same protein called keratin, which is also found in human skin, teeth, fingernails and toenails. Hard keratin is a structurally strong and remarkable protein that is resistant to wear and tear. A healthy hair can stretch up to 30% of its length, can absorb its weight in water and swell up to 20% of its diameter. A single scalp hair can hold a weight of 100g if it is in good condition.
Amino Acids - It is made up of long chains of amino acids. These chains are made up of the elements carbon, oxygen, hydrogen, nitrogen, and sulfur which are joined together by peptide bonds.
Peptide Bonds - Long chains of these peptide bonds are called polypeptide chains. The polypeptide chains are joined by side bonds.
Side Bonds - There are three types of side bonds: salt bonds, hydrogen bonds, and disulfide bonds.
Why do I need to know about these bonds?
Salt Bonds - Are broken by pH changes in the hair in both acid and alkaline direction. It is easily broken when a substance of a pH of 5.5 or greater is applied. Readjusting the hair’s pH will reform and stabilize these bonds. Salt bonds account for nearly 1/3 of the hair's strength.
Hydrogen Bonds - Are responsible for up to 30% of the strength and up to 50% of the hairs elasticity. They are the most flexible and are easily broken by water and heat to allow a temporary change to a new shape. Methods of the change of shape by stylings can occur by wet to dry and heat to cool.
Disulfide bonds - Are fewer, but are much stronger. These bonds cannot be broken by water or heat. Only chemicals agents can break these bonds, like perms, relaxers.
What are the terms for hair states of shape?
Alpha Keratin - Hair in its natural state of curly, wavy or straight is described as being in an alpha keratin state.
Beta Keratin - When hair has been shampooed or wet down, stretched and dried into a new shape it is described as being in a beta keratin state. Wetting the hair or humidity in the air will break the temporary bonds again and return the hair to its natural state.