Hair! Our bodies are covered in it, we spend a lot of time, money and effort on it and it can communicate volumes about us to others. In this blog I look more closely at the hair fibre what it is made of and share some interesting facts about hair, OK I think they are interesting, but then I find hair very interesting :-).
In school I originally learned that hair was on our bodies to regulate temperature but was confused by what I observed, people who evolved in hotter climates had thicker and more hair than people who evolved in cold regions, think Africa versus Scandinavia. I am overly simplifying here, but hair does create an insulated layer of air that helps to keep our delicate bits e.g. our head that hosts our brain, regulated; not too hot. This protective remit extends to the all important UV protection as the skin underneath is more easily prone to UV damage than the hair. Now it started to make more sense and further wondered in generations to come will we stop growing hair altogether as technology clothes our bodies, regulates our homes/offices and even in the future may control the climate.
Back to the present day, in order for hair to perform its function it has a very complex structure. The structure is made from a protein called keratin which is the same protein our nails are made from. It is also common in animals too from rhinoceros’ horn to whale baleen, it is strong stuff.
Keratin itself is made from building blocks of amino-acids, about 85% of the total hair and there are about 20 different amino-acids our bodies produce in growing hair. These amino-acids are essential-acids which means you need to feed the body protein (any protein) for them to be able to form. That does not mean if you eat more or less protein you get more or less hair, our bodies are very good at regulating what it needs from our food sources.
The hair’s structure consists of three layers; 1) the cuticle, 2) the cortex and 3) the medulla. We all have a cuticle layer, the hard, protective outer layer. We all have a cortex which is the bulk and main part of the hair. But not everyone has a medulla and even if they do, that does not mean that every single hair on their head will contain a medulla, it is generally found in thicker hair.
The Cuticle Layer; even with a simple magnification it is possible to see the scaly surface of the hair’s cuticle. The unusual hardness of the cuticle may even leave groves on much-used combs. The cuticle layer or should I say layers form a scale like pattern similar in appearance to fish scales, containing on average between 8-12 layers and is the same in all humans. The cuticle accounts for only 13.5% of the entire hair fibre volume. This thin effective cuticle makes a really hard shield protecting the fibrillar part of the hair shaft against damage from the outside while still allowing moisture to pass through its unique composition.
- Outer cuticle: The A-layer with its fatty layer known as the F-Layer a molecular layer of lipids on the outer most cuticle layer forming a boundary between the air/water and the hair form the outermost part of the cuticle called the Epicuticle. Conditioning products try to mimic F-layer as it also helps to not only protect the hair but also prevent moisture loss from within. The cells in this outer surface are formed of high-Sulphur proteins condensed to form a highly cross-linked shield capable of absorbing short wave ultra-violet radiation of the sun and also creating a mechanical stiffness.
- Inner cuticle: The Exocuticle is also made from Sulphur rich proteins filling about half of cell volume and the Endocuticle which is made up of softer cells lower in Sulphur allowing this layer to absorb moisture and the transfer of ingredients into the hair.
- Inner most layer; Cuticle fringes are the layers where the cuticle meets the cortex.
Generally; the hair is hydrophilic but the outer most surface is hydrophobic (water hating)
The Cortex has another structure which is (OK personal alert) fascinating, the individual amino acids join together at a molecular level forming chains called polypeptide chains. One particular amino acid our hair is rich in is cysteine this amino acids forms the strong bonds between the molecules called disulphide bonds which give the hair it’s rigidity and resistance. We learn a lot about these bonds when perming, straightening and relaxing hair and they are also affected when we bleach the hair. The polypeptide chains form a coiled shape known as an alpha helix. The alpha helix or in the case of a single strand of hair the alpha keratin twists together to form a protofibril. The protofibrils join together into a multi-stranded cable that is called a microfibril and hundreds of these microfibrils are cemented into an irregular fibrous bundle called a macrofibril.
This twisted structure is so strong it has been copied for generations in making ropes, have a look at an old rope and you will see the individual twisted strands coming together into the larger twists of the rope and the greater the quantity of twisted strands coming together the larger this rope. The same is with the hair, the macrofibrils intertwine into larger macrofibrils which join together to form the cortex cells (cortical cells) and finally making the cortex or main body of the hair fibre. As with the rope analogy the number of macrofibrils twisting together will influence the size of our hair.
The different amino-acids bring different properties and have a unique function within the hair, Alanine is lipophilic (it likes oil), Serine is hydrophilic (it likes water), both influencing as well as others the hydroscopic nature of hair, I like to relate this to how our hair changes in different humidity. It also gives us the ability to wash, condition and style our hair. Glutamic Acid is anionic (negatively charged) whereas Arginine is cationic (positively charged) influencing the hair it’s pH, click here for my blog on pH. When we talk about chemistry, pH is very important as both the hair’s pH and the product’s pH need to work in harmony; delivering results we want without or at the very least minimising the damaging to the hair.
The remaining 15% of the cortex is made up of 10-13% water which varies based on the humidity of the environment you are in and this water is vital for its physical and chemical properties influencing elasticity and how our hair responds to the products we put on it. For instance, 90% relative humidity, as in foggy weather or in tropical regions, our hair could potentially stretch up to twice its original length and it swells by about 16% in diameter. Our hair is dynamic, it will behave differently e.g. it could be limper, frizzier, curlier or static depending on the environment or the time of the year. The final percentage of the hair is made up of lipids, melanin, and trace elements; tiny amounts of vitamins, nitrogen, sulphur and even metals like zinc and iron.
The Medulla; is the third type of hair cells in our hair; the medullary cells are located in the centre of the hair. The medulla forms an additional inner plane of reflection, which may contribute to hair shine. Thick, especially dark hair of European or Asian origin always has a medulla. The original function of the medulla is to enhance the thermal insulation properties of hair and because this central honeycomb structure has no bearing on the products we use or develop it is a nice to know rather than a need to know. One observation that is quite interesting is that when hair containing a medulla turns grey/white, the medulla gets larger resulting in a smaller cortex area which could potentially explain why some thicker hair types appear translucent when coloured artificially. We often assume it is the hair resistance to colour but it could also be that the hair has a reduced capacity to contain sufficient dyestuff.
My big revelation when studying the hair was that it has its own chemistry and that chemistry is unique to all of us which helps explain when we put a controlled chemistry e.g. a an oxidative hair colour, it will react with our hair’s unique chemistry resulting in no two colours behaving or looking the same. That’s why so many products exist, we all need to find our hair’s perfect chemical partner.
Next time I will take a closer look at the hair’s melanin.
Caroline
