Sunday, May 16, 2010
Chemistry of your hair: Straight, curly, and frizzy hair!
Any textbook you read on curliness of hair will usually start with the disclaimer - "curl or crimp is not well understood" - meaning even the scienticians really aren't sure why this happens because there are so many factors at play.
There are three basic factors they think affect the curliness of your hair - the shape of the hair follicle (think of this as the mold for your hair strand), the distribution of disulphide (or disulfide) bonds, and the growth of your specific hair strands.
Remember the A-layer and the exocuticle? They are partially composed by sulphur rich proteins like cystine. In straight hair, these disulphide bonds are evenly spread out over the hair shaft. In curly hair, they are distributed more on one side than the other, leading to a kink or curl.
This is how a perm or relaxing treatment works - it breaks down the disulphide bonds and reforms them with a neutralizer. When you straighten or curl your hair with an appliance, you're re-arranging them temporarily. For those of us who can't take a curl or can't straighten our hair, well, you've got some powerful bonds on your hair!
As for the hair growth, our hair strands grow in a helix shape - if opposite sides of the hair grow at different rates, you'll see a twist or curl in the hair strands.
So why did you start life off straight and end up curly? Pick an option above. No, wait, your follicle shape and size won't change, so it's likely something to do with either the sulphur rich proteins in your hair or the growth pattern changing.
What's the deal with frizzy hair? Blame your genes! Your hair fibres roll themselves around the axis of the hair shaft, and there are different growth patterns around this axis, like with the curly girls. The frizziness comes out of the absorption of water in the endocuticle. It can absorb water from the atmosphere, which plumps up our hair strands. If you have hair with more disulphide bonds on one side or have hair that grows differently, you'll see frizziness there. But frizzy hair doesn't absorb water uniformly - again, you'll have more water on one side and less on the other, so you get that uneven look that leads to the frizzies! (The nice thing is we can deal with this issue with silicones and other anti-frizz products.)
Join me shortly for more about our hair - what defines "good condition"?