Have you ever sat at a hair salon and wondered why your hair and the hair on the heads of people next to you are so different not just in natural hair color but also texture? Well if you have, this post might just be your cup of tea; and if you never thought about it during your haircut session, it looks like you have a chatty stylist/something more fun to do than question things around you!!
(Image source: wikkimedia commons)
In order to understand why people have different hair colors and textures, we need to first take a look at the basic structure of a hair strand/shaft. We can broadly say that there are 3 main parts to the hair shaft. The outer most thick scale like structure is called the Cuticle. The cuticle layer is colorless and allows light reflection, so it plays a big role in having shiny lustrous looking hair 🙂 Over brushing of hair and too much friction can damage the cuticle (that is why they say backcombing is bod news in the long term).The Cuticle is followed by the Cortex which forms majority of the fiber mass of a hair strand. The Cortex contains spindle shaped cells which are aligned parallel to the central axis of the hair strand. Finally, at the center of the hair strand you have the loosely packed porous region called the medulla.
(Image Source: Wikkimedia Commons)
When it comes to hair color the Cortex is the most important layer. This layer in addition to the spindle shaped cells also contain the pigment cells (melanin). The type of melanin and its distribution in the Cortex determines the persons natural hair color. There are 2 types of Melanin pigments : Eumelanin and Pheomelanin. All human hair colors have both these types of pigments present, but its the ratio is which they are present which ultimately decides if you have blonde,red , brown or black hair.
Black to brown hair: A higher amount of Eumelanin pigment is found in these indivuduals as compared to Pheomelanin.
Red to Blonde : A higher amount of Pheomelanin (with red hair having the highest) compared to Eumelanin.
Grey Hair: No melanin pigments!
The type of hair you have on your head is greatly influenced by your race. Broadly there are 3 races: Mongoloid, Caucasian and Negroid, with all of them having very distinct hair types. It all comes down to the differences you see when you take the cross section of a hair strand/shaft. Scientists have found that mongoloid hair is straight and has a circular cross section. Interestingly, Caucasoid hair can be straight, wavy or curly but still give the same type of cross section; elliptical. Negroid hair on the other hand has a larger diameter and flattened elliptical cross section. So why is the cross section shape so important you might ask?
Lets go back to the hair cortex. We all know that keratin, a protein is the primary component of hair. Proteins are made up of amino acids and they link together to form longer chains. One of the amino acids involved in keratin strands is cysteine which has a sulfur group which is capable of forming bonds called disulfide bonds with other sulfur groups. Hence, the cysteine residues in adjacent keratin strands are able to form bridges or links through disulfide bonds. A very round shaft (circular cross section) allows less disulfide bonds, and those that are present are in line with one another, resulting in straight hair. The flatter the hair shaft(flattened elliptical cross section), the curlier hair gets, because the shape allows more cysteines to come in contact with one another and form the necessary disfulfide bridges. In other words, the more the interaction between the cysteine groups of different keratin strands, the tighter the curls get !!
Hence although we all have the same keratin protein in our hair, the cross section/ shape of the hair shaft plays a huge role in determining the type of hair you have!
Hope you enjoyed this post! In the coming weeks w’ll chit chat about the hair growth cycle, what happens when you get a straightening treatment etc 🙂
1. Chemical and Physical Behavior of Human Hair. Clarence R. Robbins.
2.Rodney D Sinclair.(2007) Healthy Hair: What Is it?.Journal of Investigative Dermatology Symposium Proceedings 12, 2–5.
3.Khumalo NP, Dawber RPR, Ferguson DJP (2005) Apparent fragility of African hair is unrelated to the cystine-rich protein distribution: a cytochemical electron microscopic study. Exp Dermatology 14:311–314