Friday, May 05, 2006

Beauty in a Bottle: How Do Shampoos Work? Part 3: Interaction with Hair

In previous posts , we've talked about the ingredients in shampoo and how they're mixed together. This post talks about how shampoo actually works to clean your hair.

The reason you want to wash your hair in the first place is because it's dirty - but how does it get dirty? There are several ways: The sebaceous glands in your scalp secrete natural oils (kind of chemically similar to olive oil) that make your hair feel greasy; then you 've got perspiration which deposits salts and other junk on your hair and scalp. On top of that mess you have smoke , pollution, and dust that your hair picks up from the environment. And let's not forget the styling residue from hair spray, gel, mousse, and putty you might have used. Now, you might think that getting this stuff off your hair would be simple, but the process of cleansing is really ingeniously sophisticated.

For the most part, all this residue on your hair is not very water soluble - in other words if you just rinse your hair in water you wouldn't get rid of it all. Enter the shampoo with its surfactant (aka detergent) molecules. These molecules are designed to remove these water insoluble contaminants by working as tiny chemical bridges. (They link oil and water together.)

If you were to look at these molecules under a microscope , you would see they consist of two parts: One end of the molecule is attracted to water, and at the other end to oil. This structure gives surfactants the unique ability to combine oil and water and it also allows them to create foam as well. This handy little piece of chemisty is the one of the most important properties of cosmetic ingredients and we'll talk about it more in a future post .

So, when the shampoo is applied to your dirty hair, these tiny chemical cleansers spring into action and "seek out" the drops of oil, dirt, and yesterday's Sebastion hair spray. The surfactants actually surround these contaminants and lift them off your hair. Once all the undesirable dirt is lifted off your hair the surfactants keep it suspended in the rinse water so it goes down the drain, not back on your hair.

So there you have it - that's how shampoo cleans your hair. And if you're wondering how a 2 in 1 shampoo cleans and conditions your hair at the same time, well, that's a different post!

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