Key concepts
Chemistry
Water
Oil
Surfactants
Foams

Introduction
We lather our scalps with shampoo all the time. But what exactly makes a good shampoo? You might be surprised to hear 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 is best for the consumer. One of these tests assesses the foaming behavior of the shampoo. 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?

Background
Although many different shampoo products are available in stores, they all have the same purpose: to clean dirt and greasy oil from your hair and scalp. How can shampoos remove all this built-up oil? For this, shampoos contain specific ingredients called surfactants, which are the main ingredients in shampoos besides water. Surfactants have a useful chemical structure that has a hydrophobic (water-repelling) tail and a hydrophilic (water-loving) head. This property allows them to react with both water and oil, which normally doesn’t mix with water.

Read More: scientificamerican.com