I decided to try something new today and write a little about the science of hair and hair care. Let me know if it’s interesting or my engineering geekness is showing 🙂
There are three parts of the hair: cuticle, cortex, and the medulla. The cuticle protects your hair from damage and looks like a bunch of scales. The cuticle strengthens your hair; if your cuticle is damaged, your hair will be brittle. One way to test for cuticle damage is by shampooing, conditioning, and then combing. If the hair sticks to the comb and makes it difficult to move, your cuticle has damage. Another thing to take into account is the pH of shampoo or anything going into your hair. pH is a measure of acidity of a solution. More acidic solutions shrink and stiffen the cuticle whereas alkaline solutions soften the cuticle. Your hair needs to be a balance of acidity and basicity, but studies have shown that more acidic hair is healthier.
The cortex is the biggest part of the hair. It looks like an old school telephone cord. With this structure, it’s more elastic and flexible. (Side note: if your hair is not elastic, that means the cortex may be damaged). When a cuticle is damaged, you might have split ends, or frayed cortexes. The medulla is in the center. This is more common in thicker hair, as it’s just a spongy core.
Is the hair you see actually dead?
The hair starts underneath the skin in the follicle which is basically this tiny hole in your skin. At the bottom of this hole, there are cells that grow and make the hair. Once the hair leaves the skin, it’s dead as a doornail. So, the part you see (the shaft), is not alive. This means that you can’t really heal your hair once it’s damaged. Unlike a scab on your skin, there is no real healing mechanism.
How does my hair get shiny?
Sebum, or oil, keeps our hair shiny and fills gaps where the hair cuticles have been depleted. Sebum has wax and fats which smoothen the cuticles. When the cuticles are smooth, light can easily be reflected, making it look shiny. Curly hair has less smooth cuticles – making it look less shiny. However, too much sebum and your hair looks oily – and oil can stick dirt to your hair. Too much oil can also clog the follicle and prevent hair growth.
Shampoo uses soaps or detergents to get rid of the oil. Detergents are solutions of surfactants. Normally, as the old axiom says, oil and water don’t mix. Surfactants change the properties of the water so that it can first wet the oil. Shampoos with detergent are actually preferable because they are not alkaline and don’t leave calcium deposits, making your hair look dull and lifeless. Too much shampooing and the sebum that protects your hair is all gone, making your hair look dull and damaged. Conditioner on the other hand creates a waxy coating over the cuticle and strengths it as well. By putting a waxy coating over your hair, you’re making the cuticle smoother and making light easier to reflect off of it.
Why is my hair curly?
Curliness has two factors: the shape of the hair in the follicle and where the keratin proteins are. Keratin proteins make up your hair, skin, and nails. The cortex of your hair is made up protofibrils which is a collection of four keratin proteins. These keratin proteins are attached using hydrogen bonds (bonds of a hydrogen atom to an oxygen atom); this bond is relatively weak. For straight hair, these hydrogen bonds attach to other keratins at the same site, making a very uniform and organized hair. For curly hair, they attach haphazardly, causing bends and twists in the cortex and then in the hair. Since these hydrogen bonds are so weak, water can break them. When the hair redries, the hydrogen bonds will reform.
The hair’s form when dry will depend the form the hair is when it’s wet. If it’s air dried when someone is sleeping, the bonds will bond haphazardly as the wet hair is placed haphazardly. If it’s blow dried, the heat forces the hair to dry straighter. This is the reason braiding your hair when wet makes the hair curlier. The hydrogen bonds are a temporary hair shape determiner, but your natural texture comes from the amount of bridges that connect your keratin proteins are present in your hair. There is another bond that gives the hair its natural texture, disulfide bonds, or bridges attaching keratin proteins. Curlier hair has more bridges, causing the hair to bend to keep these bridges. When you get a perm, you add disulfide bonds to your hair, making your hair curlier.