Yeast are microscopic fungi, single-cell organisms of the plant kingdom. Various species are abundant throughout the environment. Brewer's yeast contains essential B vitamins including biotin, minerals including zinc, and high quality proteins. These assist in the control of shedding and promote a healthy skin and hair coat.

Brewer's yeast has been fed to pets to control fleas as it seems to create an odor from the inside out that is unpleasant to fleas. This has not been confirmed through research. It has also been said the brewer's yeast will stimulate the immune system.