Hypereosinophilic (hy-per-ee-o-SIN-o-phil-ik) syndrome (HES) refers to a group of blood disorders that occur when you have high numbers of eosinophils — white blood cells that play an important role in your immune system. Over time, these high numbers of eosinophils enter various tissues, causing inflammation and eventually damaging your organs, most commonly targeting the skin, lung, heart, blood and nervous system. Hypereosinophilic syndrome can become life-threatening if not treated.
HES can affect anyone, but it occurs more often in men, usually between 20 and 50 years of age. Symptoms of HES vary, depending on what part of your body is affected. Skin symptoms include itching and rashes, for example. If your lungs are affected, you may be short of breath and have a cough.