Eosinophilia occurs when a white blood cell type–an eosinophil–is found in higher concentrations in the blood than average. These cells develop and mature in bone marrow and make up 1-6% of all white blood cells. They have two primary functions: to destroy viruses, bacteria, and parasites and to create an inflammatory response. The inflammatory response helps the immune system control its response at the site of infection. However, if the number of eosinophils is too high, the cells can build up in the tissues and cause damage to internal organs.
There are numerous causes of eosinophilia, and it may take several visits to the physician in order to determine the cause. Because the eosinophils may be found in multiple locations throughout the body, it may be necessary to see more than 1 specialist in order to determine the cause of eosinophilia. Sometimes the cause is easily treated and the eosinophilia is cured, and other times it can be due to a chronic condition.