Explanation: How does sea foam form?

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When you shake up your warm drink, proteins and fats in the milk act as “surfactants” that trap air bubbles and make foam. There are surfactants in sea water, too, which come from proteins and fats in decaying marine life. When seawater is mixed by wind and waves, air is trapped by the surfactants and sea foam forms.

An infographic of sea foam showing that decayed marine life breaks down into surfactant molecules, which form the spherical micelles that lead to sea foam. For a full transcript of the infographic, please visit https://www.noaa.gov/education/resource-collections/special-topics/hands-on-science-activities/sea-foam/explanation. — Sea foam is made up of micelles, which are small spheres made of surfactants surrounding air. These surfactants are proteins and fats that came from decaying marine life, like plankton. (Image credit: Kaleigh Ballantine/NOAA Office of Education)

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Infographic transcript

How does sea foam form? Like filling up a bubble bath or steaming a latte, sea foam forms when certain molecules in the water are mixed until they’re frothy. In the ocean, DECAYING MARINE LIFE releases organic molecules, including proteins and fats, into the water. Some proteins and fats can act as SURFACTANTS. Surfactants have a hydrophilic or “water-loving” end that is attracted to water and a hydrophobic or “water-fearing” end that is repelled by water. This dual nature means that these molecules end up collecting on surfaces – the surface of the water, an air bubble, a particle of dirt, or a droplet of oil, for example. Surfactants form spheres called MICELLES with their hydrophilic ends in the water and their hydrophobic ends pointing toward the surface. In the case of sea foam, wind and waves mix the water, and surfactants form micelles around air bubbles, stabilizing them so the bubbles don’t pop right away. This is how sea foam forms.

“Surfactants,” short for “surface active agents,” are found in many places: soaps and detergents, industrial processes, foods, and even our own bodies! Let’s take a closer look at how they work.

One end of a surfactant molecule is polar. This end is called “hydrophilic,” or “water-loving,” because it orients toward water, which is also a polar molecule. The other end of a surfactant molecule is nonpolar. This end is called “hydrophobic,” or “water-fearing,” because it orients away from water.

This dual nature means that these molecules end up collecting on surfaces — the surface of the water, a small particle of dirt, an air bubble, or a droplet of oil, for example.

Surfactants group together around non-polar substances, forming spheres called micelles. When you wash your hands, for example, surfactants in soap form micelles around oil, dirt, and germs, which can then be rinsed away, leaving you with clean hands. In the case of sea foam or a foamy drink, micelles form around air bubbles that get trapped as the liquid is mixed. The micelles stabilize the bubbles and prevent them from popping right away.

A student crouching down in front of sea foam holding a handful of foam and smiling at the camera. — A student learning about sea foam formation grabs a handful of sea foam on the Oregon Coast. (Image credit: Courtesy Denise Harrington)