What makes soap lather?

[Eonwe]

Does anyone know what makes soap and shampoo lather and get all foamy? I think it might be fun to make my own, and I’m not sure what ingredient causes this.

[Duck_Duck_Goose]

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Question:
Why does soap lather?

The following answer comes from Procter & Gamble’s Ivory Soap USA Correspondence team (yes, they have a whole team):
Lather is made from the bar solids and water. This is actually a result of air and water interfacing with the cleansing surfactants. That’s where friction between the bar and body (or washcloth) takes place.

Soap ingredients have water-loving and oil-loving parts. The oil-loving parts scoop up the oily soil from your skin and the water-loving parts suspend the oily soil so it can be rinsed away by water.

Some of the causes of poor lathering would be a high mineral content in the water, cool water temperatures, greasy or oily soils on the skin or leaving a bar in a soap dish or other location where it’s constantly bombarded by water.

Related web sites:
Soap as an emulsion from the University of Southern Mississippi
How Soap Works from Bockstanz, Inc.

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Question:
What makes soap lather?
–Felecia Harris,
Highland Springs, VA.

George Feighner, a chemist at Scientific Services, a cleaning products laboratory in Sparrow Bush, New York, responds:

Soap molecules are long chains of atoms that have two main parts: a polar “head” that is attracted to water molecules and repelled by grease, and a hydrocarbon tail that is repelled by water and attracted to grease. The hydrophobic (literally, “water fearing”) tails of the soap molecules naturally try to get out of a watery solution and collect at any available surface. When that surface is air, the soap molecules arrange themselves in an orderly layer, with the hydrophilic (“water loving”) heads in the water and their grease-loving tails in the air. Shaking a soap-and-water solution introduces pockets of air that, when big enough, appear as bubbles. A thin film of soap molecules coats each pocket, creating a bubble. When the shaking stops, the bubbles float to the surface. More soap and more stirring allow the formation of smaller bubbles. Foam or lather is just a conglomerate of these tiny soap bubbles. Although many people associate lather with the cleaning properties of soap, it is actually an incidental property resulting from the way the soap molecules are drawn to dirt and grease. In fact, too much lather is detrimental to laundering clothes because it can overflow a washing machine and hinder agitation. To combat this problem, chemists have invented detergents that do not lather.

RELATED WEB SITES:
For a brief introduction to the science of bubbles and soap from San Francisco’s Exploratorium, see: www.exploratorium.edu/ ronh/bubbles/bubbles.html.