Why Is Milk White?: & 200 Other Curious Chemistry Questions (2013)

How do they make shampoo in different colors?

The main detergents in most shampoos are sodium lauryl sulfate and sodium lauryl ether sulfate (sometimes called sodium laureth sulfate). These are white solids or powders in their pure form, and when dissolved in water they form a thick liquid that is very slightly off-white, like lemonade.

Shampoo manufacturers generally like prettier colors than that. They may add natural colors like tea extracts and plant dyes such as henna, beta carotene, and annatto, but these may require additional preservatives to keep them from spoiling during storage.

The Federal Food, Drug, and Cosmetic Act regulates food and cosmetic colorings, among other things. Some colors do not require certification by the FD&C because they are “Generally Recognized As Safe,” or GRAS. These include such things as caramel color, beet juice, cochineal extract, saffron, mica, and beta carotene.

Unlike the colors that do not need to be certified, which contain a mixture of different compounds, each FD&C certified color is a pure compound. There are seven lists of colors. The first list is colors that are allowed in foods. The second list can be used in drugs and cosmetics. The third list is for only externally applied drugs and cosmetics. The other lists either exempt colors or add further restrictions.

The first list contains the FD&C colors. You may have seen these in the ingredients list on foods you have eaten.

· FD&C Blue #1

· FD&C Blue #2

· FD&C Green #3

· FD&C Red #3

· FD&C Red #40

· FD&C Yellow #5

· FD&C Yellow #6

The colors in the second list are not to be used in foods, and so the F is not included in the name. Some examples are:

· D&C Green #5

· D&C Orange #5

· D&C Red #6

· D&C Red #7

· D&C Red #21

· D&C Red #22

· D&C Red #28

· D&C Red #30

· D&C Red #33

· D&C Red #36

· D&C Yellow #10

Carmine (also known as cochineal extract) is one color that may surprise many people. It is made from the body and legs of a female scale insect that lives on cactus plants. Almost onequarter of the dry weight of these insects is carminic acid, which the insects produce to prevent other insects from eating them. This is mixed with aluminum or calcium salts to make the red dye called carmine. You have probably eaten something colored with this dye, made from little tiny bugs.