Fancy Foams with Shampoo Science
Do you like your hair shiny and beautiful? The key to keeping your hair nice and clean is to use a good shampoo. But what exactly makes a good shampoo? You might be surprised to hear that every new shampoo has to pass lots of scientific tests before it is considered good enough to be sold. Many different shampoo recipes are compared to decide which one is the best for the consumer. One of these tests assesses the foaming behavior of the shampoo. You probably trust a shampoo that makes lots of foam more than one that doesn't make any foam at all! In this activity, you will become a cosmetic scientist and put different shampoos to the test. Which brand do you think creates the most foam and which foam lasts the longest?
Shampoo is by far the most common product used for hair treatment across all hair colors and lengths. Although many different shampoo products are available in stores, they all have the same purpose: to clean dirt and grease from your hair and scalp. If you have too much grease in your hair, it looks oily. How can shampoos remove all this built-up grease? For this, shampoos contain specific ingredients called surfactants, which are the main ingredients in shampoos besides water. Surfactants are unique chemicals as their chemical structure has a hydrophobic (water-repelling) tail and a hydrophilic (water-loving) head. This property allows them to react with both water and grease, which normally doesn't mix with water.
Although its cleaning power is probably the most important criteria for a good shampoo, there are many other aspects that decide the quality of a shampoo. Besides surfactants, there are also additives in each shampoo that optimize its look, feel, smell, or performance, such as additional foam builders, thickeners, conditioning agents, or preservatives. For example, the ability to create lots of foam and the stability of the foam is important because people associate more foam with more cleaning power. Although this is not necessarily true, a shampoo sells much better if it makes more foam. Therefore, additional surfactants that have a strong capability to produce foam are used as foaming agents.
Scientists constantly research new shampoo recipes and have developed specific tests to assess every new product they create. This allows them to compare different shampoo recipes to find the one formula that performs best overall. In this activity, you will perform such a test yourself and find out which of the shampoos in your selection creates the best and the longest lasting foam!
- A selection of different shampoos
- Cups (8 oz.), one per shampoo
- Kitchen scale
- Tap water
- Measuring spoon (1 tbsp.)
- Tall, narrow glass or vase (> 8 oz.), preferably with lid.
- Permanent marker, two different colors
- Paper and pen
- With the permanent marker, label each cup with the name of the shampoo you want to test.
- Make a 10% solution of each of your shampoo samples. To do this, put one empty cup on the kitchen scale and zero it. Add 20 grams of your shampoo sample and then add tap water to the cup until the scale reads 200 grams.
- Carefully mix the shampoo with the water by stirring with the spoon.
- Repeat steps 2 and 3 for all of your shampoo samples. Clean your mixing spoon between each sample.
- Get your tall, narrow glass, and carefullypour 50 mL (about 6 tablespoons) of the first 10% shampoo solution inside. When pouring the shampoo into the glass, do you already see any foam formation?
- Have a timer ready and set it to five minutes.
- Put the lid on the glass if you have one. Then take the glass between your hands and shake it very hard for ten times up and down. If you do not have a lid, use the palm of your hand to cover the glass and seal it off the top. Do your best to keep the shaking speed constant for all shampoos. What happens once you start shaking the shampoo solution?
- Immediately after you are done shaking, start your timer. Use a marker to make a mark on the glass at the level at which the foam phase starts (at the bottom, right above the liquid) and where it ends at the top. How much foam did the shampoo produce?
- To assess the foam stability, or to determine how fast the foam disappears, make another mark of the foam level (top and bottom) on the glass after five minutes using a different color. Note: The foam level is likely to change most at the interface between the liquid and the foam, not at the top of the foam layer. What happens to the foam over time? Do you have more or less foam after five minutes?
- After you have marked the foam levels, clean out the glass (make sure all the shampoo and foam is removed) and look at the different marks you made. Take a ruler and measure the distance between the top and bottom level of the foam layer at the beginning and after five minutes. Write your results down on your paper. How did your foam volume change over time? What do your results tell you about how stable the of the shampoo is?
- Remove the marks on your glass and repeat steps 1 to 7 for each of your shampoo samples. How do your results compare? Which shampoo made the most foam? How much foam disappeared for each shampoo within five minutes? Can you correlate the foaming behavior with a specific shampoo ingredient?
- Finally, repeat steps 1 to 7 with pure water. Do your results differ when using just water compared to the shampoos? If yes, why do you think this is the case?
Extra: Find out how long your foam lasts and increase the time you are monitoring the amount of foam in your glass. At what time point is the foam completely gone?
Extra: Many organic shampoo brands reduce the amount of surfactants and additives in their shampoo recipe, as these can potentially irritate the scalp. Compare an organic shampoo brand to a regular shampoo brand to see if they make the same amount of foam.
Extra: You can also make your own shampoo from recipes you find online. How does your home-made shampoo compare to the store-bought product?
Extra: What about additional tests that assess other shampoo properties such as its cleaning power? You can find instructions on how to do some other tests in the "More to explore" section.
Observations and Results
Did you create lots of foam? Most of the store-bought regular shampoo should have produced lots of foam once you started shaking it. You might have even seen a little foam formation already when you poured the shampoo solution into the glass. This is because these shampoos contain lots of surfactants and foam builders. When you shake the glass, you create lots of gas bubbles that get trapped in the shampoo solution and result in the foam you see. The surfactants or foaming agents facilitate the formation of foam and stabilize the gas bubbles in the solution.
However, the foam is not stable forever! In fact, you should have observed that the amount of foam quickly decreased over time. You probably saw that the bottom level of the foam quickly rose to a higher level because the gas bubbles in the solution eventually collapse. The volume of foam that you produce for each of your shampoos depends on how much surfactants and foaming agents they contain. Solutions that do not contain any of these substances, such as water, do not create any foam, which you should have noticed in your last test.
Ask an Expert
- Rinse out the glass and each of the cups you used and clean your work area.
- Shampoo, from How Products are Made at Madehow.com
- Secrets of Shampoo, Special to The Washington Post
- Types of surfactants in your shampoo, from hairmomentum.com
- Make Your Own Shampoo and Test How It Performs!, from Science Buddies
- Science Activity for All Ages!, from Science Buddies