The eosinophil is a cell of the immune system, with an arsenal of substances that can alter the balance that exists in the different organs where they are found. With the advent of monoclonal antibodies, concern about their depletion has become an important turning point in their formulation. For this reason, it is of vital importance to investigate the consequences of the mechanism of action of biological agents, in the short and long term. This review tries to show the role of eosinophils in both homeostasis and disease, and their relationship and interaction with monoclonal drugs in diseases focused on the Th2 profile. It is expected that this article can be useful when making the decision to start treatment with monoclonals, specifically anti-interleukin-5 or against its receptor