The science of hair

I don't know about you but hair is a major annoyance in my life.

I have inherited parts of my mum and dad's hair (in terms of DNA). Being mixed that is my dad's thick curly afro hair crossed with my mum's dark lusciously thick straight shiny hair. This has left me with thick frizzy hair that certainly has a mind of its own. Looking around and seeing people with tame hair, I definitely was a little jealous but overtime that love hate relationship has ended and I have grown used to my unruly unpredictable hair.

This however doesn't mean it isn't an annoyance in my life. I have to make sure I don't wash my hair too often as it becomes overly dry, I can only brush it before I shower with lots of coconut oil for the knots, I have to put it up in a bun when I sleep, brushing takes an hour of my life which is extremely painful even with a tangle teaser and the floor of the whole my room ends up looking like a Yeti. Yes I have more rules and structure to my hair routine than my entire life.

After nearly 3 years straighteners free, I have started wondering; how is my curly hair structurally different to someone with straight hair?  How do straighteners eliminate this difference for a few hours? How about chemicals? What does the future hold?

Human hair comes with all sorts of textures and shapes. 

How is my curly hair structurally different to someone with straight hair?

Hair is more complex than it seems. As early as 22 weeks old foetuses we reach the peak of our number of hair follicles, as they have all developed by then and when lost during our lifetime are not regenerated. Simplified, the growing hair shaft is what we see as hair and the follicle is located beneath the epidermis into the dermis where it is surrounded by blood vessels for nurishment and nerves. These two elements make up our hair. It is the difference in these that alters the curvature of our hair.

1) The follicle of a straight hair and curly hair differs. Straight hair follicles are rounded (symetrical follicle) and curly hair follicles are oval (asymettrical follicle), with a correlation of flatter oval follicles with increasingly curlier hair.  

2) The manner in which the follicle tunnels into the scalp also differs. Straight hair follicles tunnel through the scalp into the dermis vertically whereas curly hair follicles tunnel at an angle causing the hair shaft to grow curly.  The angled growth also causes limited lubrication as it ceases sebum secreted by sebaceous gland to travel up the hair resulting in dry or frizzy hair.

Hair follicles of different hair types.

3) The hair shaft is composed of keratin. Produced by keratinocytes, keratin is a vital component of hair. It is a protein composed by the combination of 18 amino acids, most importantly cysteine. Cysteine has a sulfur containing chemical group that allows it to form strong disuphide bonds with other sulfur containing molecules such as other cysteines in the hair shaft causing curling of the hair. Curly hair has an uneven distrubution of keratine in the hair shaft; accumulated near the inside edge of a curled hair, beneath the curve causing more disulphide bonds to occur in curly hair.  Hair shape is dependent on protein protein interaction. 

4) But of course genetics is very important!

How do straighteners eliminate this difference for a few hours? How about chemicals?

The increased number of disulphide bonds in curly hair are taken advantage of to change the structure  of the hair to the straight style wanted. By acting on this, hair can be altered temporarily (short or long term). Heat is an easy way of breaking disulphide bonds. When disulphide bonds are broken by the heat, keratin chains can be moved and hair becomes malleable to form the style wanted which is straight.  Bringing us to hair straighteners. However due to oxidation, mositure causes hair to revert to it's original shape therefore hair straighteners are not a permanent technique.

During relaxing hair/chemically straightening hair, a mixture of chemicals break the disulphide bonds permanently. Strong reducing agents which are bases/alkaline eg sodium or calcium hydroxide, thioglycolate or bisulphate break the disulphide bonds, the hair is kept straight and the acid is added to stop the disulphide bond cleavage reaction and allow the disulphide bonds to reform in the straight shape. Although currently the only permanent solution, this technique damages hair. 

What does the future hold?

A safer future alternative may be drugs...

Even if you're born with symmetrical follicles, there are ways in which straight hair can turn curly. Scientists have found that a cellular receptor called EGFR clusters on the outer root sheath of a follicle and appears to regulate the growth of hair. Certain cancer drugs that inhibit these receptors may cause a patient to develop curly hair as a side effect. Therefore inhibitors to EGFR may be used as a way to get curly hair and a promoter to EGFR may be used as a way to straighten hair.