Eosinophilia is a condition in which the body produces an abnormally high number of eosinophils, a type of white blood cell. The condition is often associated with allergies, asthma, and certain parasitic infections. Synonyms for eosinophilia include eosinophilic disorder, eosinophilic infiltration, eosinophilic syndrome, and hypereosinophilic syndrome. Other related terms include eosinophilic granulomatosis with polyangiitis (formerly known as Churg-Strauss syndrome), eosinophilic esophagitis, and eosinophilic cystitis. While these conditions share the common feature of elevated eosinophils in the body, they may differ in their presentation, causes, and treatment options. A medical professional should be consulted for proper diagnosis and treatment.