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Kerosene, fuel oil and other light oil products were used to break down foam. The first defoamers were aimed at breaking down visible foam at the surface. Entrained air bubbles are agglomerated, and the larger bubbles rise to the surface of the bulk liquid more quickly. This causes rupture of the air bubbles and breakdown of surface foam. It has affinity to the air-liquid surface where it destabilizes the foam lamellas. An essential feature of a defoamer product is a low viscosity and a facility to spread rapidly on foamy surfaces. Generally a defoamer is insoluble in the foaming medium and has surface active properties. A variety of chemical formulae are available to prevent formation of foams.

They cause defects on surface coatings and prevent the efficient filling of containers. In industrial processes, foams pose serious problems.

The additive is used to prevent formation of foam or is added to break a foam already formed. Commonly used agents are insoluble oils, polydimethylsiloxanes and other silicones, certain alcohols, stearates and glycols. Strictly speaking, defoamers eliminate existing foam and anti-foamers prevent the formation of further foam. The terms anti-foam agent and defoamer are often used interchangeably. A defoamer or an anti-foaming agent is a chemical additive that reduces and hinders the formation of foam in industrial process liquids.