I remember reading a discussion of plastic illustrated with a bottle of shampoo. The author pointed out that both the plastic bottle and contents had many of the same ingredients, specifically petrochemicals. A while ago I wrote about soap and detergent. What’s shampoo?
The short answer: detergent with additives.
The molecules of both soap and detergent have a hydrophilic end, which attracts water, and a hydrophobic end, which avoids water.
I explained in more detail in my earlier article how they work, but basically the hydrophobic end attaches to oil and grease while the hydrophilic end attaches to water.
So the soap or detergent allows oil and water to mix. The oil goes down the drain with the water.
A word about hair
Have you noticed that you need to bathe and wash your hair even when you haven’t actually gotten dirty?
Skin produces an oily substance called sebum. Among other things, it coats and protects hair, but it’s greasy. After a while, it accumulates so much that strands of hair stick together and it starts to attract dust, pollen, and so on. So your hair looks dull and feels greasy.
Like all oily substances, sebum is hydrophobic. No matter how much you rinse your skin or hair, you can’t wash out the sebum.
Shampoo and its ingredients
Shampoo contains detergents, which work on the sebum on hair the same way as they do on hydrophobic substances on dishes, clothes, or anything else.
Soap or dishwashing detergent will get your hair just as clean as shampoo, but in washing away the sebum, it also washes away the protection for your hair, making it liable to damage. So besides detergent, shampoo contains conditioning agents and other protectants.
Shampoo also includes colorants and other purely aesthetic ingredients, thickeners, ingredients to hold the mixture together, ingredients to prevent bacteria and mold from growing in it, ingredients to make a rich foamy lather, and preservatives. Dandruff shampoo contains one of a variety of other ingredients. Some shampoo additives perform a useful function. Some do not.
The lather does nothing to help the cleaning or conditioning action of shampoo. Lather is important for washing your skin with soap, because that’s what captures the dirt and germs that get washed down the drain when you rinse.
Shampoo and other detergents work differently from soap. The only reason they make a lather is because consumers think it’s what makes them effective!
Manufacturers have certainly not made it easy for the public to be well informed. Consider the cliché “lather, rinse, repeat.” That instruction used to be on every bottle of shampoo.
When I was a child, people treated their hair with a variety of oily, greasy stuff. I can’t speak for women’s products, but I certainly remember a lot of men’s products.
A TV show I used to watch was sponsored by Wildroot Cream Oil, a hair care product. (Their jingle started, “Get Wildroot Cream Oil, Charlie,” and before I could read I thought Charlie was the last word of the product’s name.)
Some time later, I think, Brylcream came on the scene as an alternative to “greasy kid stuff,” but it was still some kind of goop men and boys were supposed to use when combing their hair to keep it looking combed all day.
When it came time to shampoo, all of that greasy stuff interfered with the lather. Rather than telling the public that the lack of lather didn’t mean that your hair wasn’t clean, manufacturers instructed consumers to put more shampoo on their heads.
Since their hair was almost certainly clean by that time, the only point of using more shampoo was to provide a showy lather so the consumer could be convinced it was working. That and the convenient fact that applying shampoo twice meant running out of it sooner.
Between using less goop in the first place and continued refinements in shampoo formulas, “repeat” is less justified now than it was 50 years ago. I looked at various brands of shampoo. Some say just “rinse thoroughly.” Others advise to “repeat if desired.” Some still have the instruction “lather, rinse, repeat.”
And, of course, lathering twice conveniently increases the need for conditioner. Presumably, since shampoo already contains conditioner, more conditioner isn’t necessary for people who lather only once. You’ll never learn that from any marketing department!
Alternatives to shampoo
For centuries, soap was the only game in town. As I said in my earlier article, soap has one big drawback (besides the unavoidable harshness of soap until fairly recently).
Minerals in the soap combine with minerals in the water to form soap scum. You know how hard it is to scrape it off your bathtub. If you use soap to wash either hair or clothes, the same scum forms, making hair or clothes look dull.
In my research for these articles, I came across a blog post touting a brand new eco-friendly alternative to detergent. No petrochemicals at all! It’s pure soap! What could be better? It’s pure, unalloyed, earth-loving bliss! That is, if you don’t mind dull, scummy hair.
I have searched for a scientific explanation of how it works, but haven’t found one. Anecdotal descriptions are almost uniformly positive. The exceptions seem to be people who didn’t dilute the borax in a lot of water. I use it myself and like the results just fine.
Most people who like to use borax for their hair use apple cider vinegar if they feel they need a conditioner.
How shampoo works / About.com Chemistry
Lather, rinse, repeat: hygiene tip or marketing ploy? / Laurie Goldstein (Fortune, October 11, 1999)