It seems like it’s been forever since I’ve written a passion blog post! My last was an investigation of what exactly is in laundry detergent, how it works, and an intro to some of the chemistry behind why it works. In a similar vein, this week I’ll turn the microscope on something each of us uses (hopefully!) every day—shampoo. (Thanks to Sarah for suggesting the topic!) I have to say I’m a big fan of long showers, and sometimes you just don’t want to step out into the cold just yet, but you’re getting a bit bored just standing there. So what do you do? Read the shampoo bottle, of course (…or am I the only one?) The ingredients list is my personal favorite—I always try to pronounce the long, complicated chemicals and compounds, some upwards of 30 letters. But more importantly, I’ve always wondered what each does. What exactly is shampoo, and why does it need so many seemingly complicated ingredients to get some dirt out of my hair? Let’s find out.
Above is a picture of my the ingredients list of my personal shampoo bottle—Suave, to be specific.
The first shampoos were similar to typical bar soap, but as it turns out, modern shampoos are actually closely related to the laundry detergent I previously described. That’s not to say that they are identical, but they function on the same premise. They both use surfactants to get rid of dirt and grime, only this time the dirt is on your hair instead of your clothes.
Now let’s go through the list.
Water: The base into which all the other ingredients are added: the foundation of the shampoo.
Sodium Laureth Sulfate: A surfactant and foaming agent (it removes dirt and helps create that nice lather). SLES can cause skin irritation.
Cocamidopropyl Betaine: Another surfactant and foam booster. It’s name sounds like “coconut” because it’s derived from coconut oil.
Sodium Chloride: Table salt. But what’s it doing in your shampoo? It’s used as a thickening agent.
Fragrance: To make your hair smell fresh and clean (but shampoo manufacturers aren’t required to list the specific chemicals in their “proprietary” fragrances)
Tetrasodium EDTA: Full name: tetrasodium ethylenediaminetetraacetic acid (that’s “tetra-sodium eth-ul-lean di-am-mean tetra-aceetic acid” if you want to say it out loud). I actually used this chemical in my chem lab last semester. It’s technical term is a chelating agent. The problem with tap water is that it’s often “hard” (meaning that it has a lot of dissolved minerals). Water hardness depends on where your water comes from—what rocks and minerals it flows through and picks up on its way to your tap. Why is this a problem? Surfactants are attracted to these minerals, so they’ll go after them instead of targeting the dirt on your hair. That’s where tetrasodium EDTA comes in—it grabs on to the minerals allows the surfactants to work on the dirt on your hair instead.
DMDM Hydantoin: A preservative for the shampoo (who knew it shampoo could spoil…) It slowly releases formaldehyde in the shampoo, which prevents microorganisms from growing in it. This is a bit controversial because formaldehyde is a known human carcinogen (in much, much, much higher concentrations that in your shampoo), but it still has some risk.
Citric Acid: The acid that gives citrus fruits their sharp taste. It’s used in shampoo mainly to lower the pH (make the shampoo more acidic). It turns out that a slightly acidic (pH ~ 5.5) shampoo will make your hair follicles lay flat, making your hair feel smooth and shiny.
PPG-9: Here we go with the abbreviations again. Its name is polypropylene glycol, and it’s a chemical that seems to be primarily used in industry as a thickener and stabilizer, but other than that I could not find what it’s used for.
Methylchloroisothiazolinone and Methylisothiazolinone: (meth-ul-chloro-iso-thia-zol-linone) Used in combination (in a dilute form) as a biocide to deter the growth of bacteria and other organisms. In concentrated form, the chemical is so strong that it can burn human tissue. Some studies conclude that it is toxic, but it is not officially classified as known or probably carcinogen.
Mentha Piperita (Peppermint) Leaf Extract: A soothing agent and fragrance. (No, you still can’t eat it.)
That’s a lot of ingredients! It can be daunting to figure out what exactly manufacturers mix up to put in your shampoo bottle, and this has lead some people to advocate for the less frequent use (or non use) of shampoos. The rationale is that shampoos strip your hair and scalp of oils, which the body in turn compensates for by producing those oils at an even faster rate—a vicious cycle of shampoo use. If you didn’t use shampoo, your scalp would simply produce less oil. Some choose instead to wash their hair with baking soda, vinegar, or even honey or just warm water.
I don’t know about not using shampoo… I think I just wouldn’t feel “clean” if I didn’t use shampoo. But perhaps the projection of regular use of shampoo as a social norm has made us feel compelled to use it every day. What do you think?
Sources:
http://www.dow.com/polyglycols/ppgc/na/products/ppgs.htm
http://health.howstuffworks.com/skin-care/cleansing/products/tetrasodium-edta-in-cleansers.htm
http://www.takepart.com/article/2013/08/28/deconstructing-your-haircare-ingredients
All images from the respective Wikipedia pages of each compound. Used under public domain.
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