Why Does Horse Sweat Appear Foamy?

A horse’s sweat can appear lathery or foamy because it contains latherin, a substance not found in human perspiration.

Latherin reduces the surface tension of water and aids moisture in moving away from the skin to the surface of the horse’s coat. This improves evaporation and cooling, a necessity considering the horse’s need to shed a large amount of heat during and after strenuous exercise.