Hypereosinophilic (hy-per-ee-o-SIN-o-phil-ik) syndrome (HES) is 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, the excess eosinophils enter various tissues, eventually damaging your organs.

The most common targets are the skin, lungs, digestive tract, heart, blood and nervous system. Untreated, HES can become life-threatening.


Early symptoms of HES may include fatigue, cough, breathlessness, muscle pain, rash and fever.


Some varieties of hypereosinophilic syndrome tend to run in families. Other types have been associated with certain types of cancers, infections or other health problems.

Risk factors

HES can affect anyone. But it occurs more often in men, usually between the ages of 20 and 50.

Hypereosinophilic syndrome care at Mayo Clinic

April 27, 2022

Living with hypereosinophilic syndrome?

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