Sunday, May 16, 2010

Chemistry of your hair: Straight, curly, and frizzy hair!

As I mentioned in the previous post, the shape of your follicles can have a great deal to do with whether you have curly or straight hair. As you can see, straight hair tends to come from very circular follicles, while curly hair comes from elliptical follicles. But there's more!

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"?


Anonymous said...

Hi! My name is Rachel and I am a high student. Right now, my partner and I are doing a project on the chemistry behind curly hair. One of the requirements for this project is to conduct an interview, but trying to find someone who is knows a lot about chemistry and hair and is willing to talk about it is a lot easier said than done! We would love to set up an interview with you, if at all possible. It would be quick and could even be over the phone or in an email. We both understand that you are very busy. Thank you for your time!


Anonymous said...

By the way, you can reach me at
Thanks again!


Kim said...

Is adding water good for curly hair? Should we be making lotions and creams for curly hair? Or should we just make anhydrous, oil-based products? What ingredients do you recommend for curly hair when formulating? Could you start a series on formulating for curly, damaged hair?

Susan Barclay-Nichols said...

Hi Kim. Yes, water is good for all hair types. No, you shouldn't be making lotions unless you're using cationic emulsifiers that double as hair conditioners as you aren't getting a benefit from a non-ionic emulsifier like Polawax. No, oil based products aren't great for curly hair as you want the positively charged emulsifiers we use to make water containing products to condition. Oils moisturize on the surface of the hair, which is great, but we really don't need as much moisturizing with oils as everyone would indicate. Add a bit of coconut oil to your hair product and see how awesome this inexpensive oil can be!

If you aren't sure about some of what I've said, can I encourage you to check out the hair care section of the blog or do a search for "hair care products" or "hair conditioners" to see more of what I've written in previous posts. Or just check out the many many many recipes I've written for all kinds of hair types by doing a search! I'm sure you'll find what you seek!