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About "Ask A Scientist!"

On September 17th, 1998 the Ithaca Journal ran its first "Ask A Scientist!" article in which Professor Neil Ashcroft , who was then the director of CCMR, answered the question "What is Jupiter made of?" Since then, we have received over 1,000 questions from students and adults from all over the world. Select questions are answered weekly and published in the Ithaca Journal and on our web site. "Ask A Scientist!" reaches more than 21,000 Central New York residents through the Ithaca Journal and countless others around the world throught the "Ask a Scientist!" web site.

Across disciplines and across the state, from Nobel Prize winning scientist David Lee to notable science education advocate Bill Nye, researchers and scientists have been called on to respond to these questions. For more than seven years, kids - and a few adults - have been submitting their queries to find out the answer to life's everyday questions.

Previous Week's Question Published: 28 June, 2006 Next Week's Question
Variety of chemicals in hair relaxers untwist strands
How do relaxers on your hair work?

As both someone who is a biochemist and has unmanageable curly hair, I think this question is good. First, we have to understand why hair is curly. There are two reasons:

One of the reasons hair is curly is because of hydrogen bonds between the proteins (keratin) that make up your hair; these bonds are weak and can be enhanced by water. That is why straight hair can curl when it is wet. The everyday shampoos and conditioners you buy in the store and use in the morning to straighten your hair (or at least "tame your curls") work because they keep moisture from penetrating the hair strands. These products do not do anything chemically to your hair except coat them with various types of oils that keep your hair from absorbing water. That is also why your hair feels especially soft and smooth after using these products. Another way to alter hydrogen bonds is with heat; electric straighteners work because of this principle. The platters on electric straighteners are flat so that when your hair cools it takes the shape of "flat" as the hydrogen bonds reform. The same thing occurs with curling irons, but since the heating element is circular, the hair stays curled as it cools. The effect of heat, however, is temporary, over time the hydrogen bonds eventually return to their original form and the hairs goes back to the way they were. This rearrangement happens because moisture in the air hydrates the proteins. Hydrating the proteins in hair causes your hair to swell and allows the proteins (which like to exist in water) to become more "at home," and your hair will take its original form again. This is also why (for those of us with curly hair) humidity gives our hair a life of its own and refuses to listen to us.

The main reason hair is curly is because the keratin proteins contain amino acids called cysteines. These cysteines link to each other by disulfide bonds (two sulfur atoms connected to each other). The more disulfide bonds, the curlier the hair. All hair has disulfide bonds but it is the shape of the hair strand itself which determines both how many and in what way the disulfide bonds are put together. Hair strands that are round have fewer disulfide bonds and the bonds are more aligned with one another thus the hair is straight. Hair strands that are flattened and look more oval like have a greater number of disulfide bonds, which are also connected askew, there fore the hair is more curly. The shapes of hair strands depend on the person, some people have round pores from which their hair grows, others have more flattened pores. Round pores make round hairs, flat pores make flattened hairs. As I said the shape of these hair strands are dependent on the person and are there fore difficult to permanently change but we can change whether or not hair is curly or straight by changing the disulfide bonds.

Relaxers simply break these disulfide bonds and cap them so that they cannot chemically reform. Classically, hair relaxers use a reducer or a base (the opposite of an acid) such as lye (sodium hydroxide) to break and cap these bonds. A good example of this method can be seen in the movie "Malcolm X" with Denzel Washington: Denzel nearly burned his hair off trying to straighten it. Unfortunately, sodium hydroxide can burn your skin and damage your hair. The gentler and safer commercial relaxers are still based on the same chemical reactions of breaking disulfide bonds and capping them. For instance, the "Imina P&G No Lye Conditioning Crème Relaxer Base-Relaxer Kit" by Procter & Gamble, according to their website, contains 5% calcium hydroxide a medium strength base. Where as "MPDiol Glycol Alkaline Hair Relaxer" by Lyondell, contains 5% sodium hydroxide, a very strong base.

Disulfide bonds are not affected by water so, when you break the bonds and cap them (in the case of relaxers) they will not go back to their original state. Perms which, intentionally curl hair, chemically increase the number of disulfide bonds by using an oxidizer to uncap the naturally caped sulfides in straight hair. As the name implies, these perms will stay "forever" curly. So, as you can see, one chemical (a reducer) can make your hair straight, while another chemical (an oxidizer) can make your hair curly. Using a combination of these chemicals in the right order allows you to be more creative with your hair. No matter what kind of hair you have, as long as you can break disulfide bonds with one chemical, shape your hair and then reform the disulfide bonds with another chemical you can get any hair style you want. Perms and relaxings both eventually go away, not because the bonds reform, but because your original hair simply grows in, replacing your straightened or curled hair with what you had originally. These chemicals, however, have a tendency to damage your hair, until eventually your hair starts to thin and break, so too much styling can be bad for your hair's health. Oh, and in case you were wondering hair sprays just glues your hair together.