Overview
Hypereosinophilic syndrome is organ damage or dysfunction caused by an excess of disease-fighting white blood cells called eosinophils.
Hypereosinophilic syndrome (hy-per-ee-o-SIN-o-phil-ik) is rare. It can affect any tissues in the body. Common targets include the skin, lungs, digestive tract, heart and nervous system.
If a condition is found to cause hypereosinophilic syndrome, then treating the underlying condition also may lower eosinophil levels. Other treatments include medicines that reduce the number of eosinophils in the bloodstream.
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Symptoms
Symptoms of hypereosinophilic syndrome (HES) vary depending on what organs are affected. Early symptoms of HES may include:
- Fatigue.
- Cough.
- Shortness of breath.
- Muscle pain.
- Swelling in deep layers of the skin.
- Rash.
- Fever.
When to see a doctor
Many different conditions can cause the symptoms related to HES. See your healthcare professional as soon as possible if symptoms do not improve.
Causes
Eosinophils are important in fighting parasites and bacteria. They also regulate other immune system cells and proteins that cause allergic reactions.
HES occurs when high levels of these white blood cells last a long time. The cells themselves or their byproducts can move into organs, where they can cause damage or dysfunction.
Terms to know
You may hear the following terms regarding HES.
- Eosinophilia is a higher than typical number of eosinophils circulating in the bloodstream.
- Hypereosinophilia is a high number of eosinophils that lasts for an extended period, usually at least one month.
- Hypereosinophilia syndrome is organ damage or destruction caused by long-term high eosinophils.
Types of hypereosinophilia
Persistent increases in these white blood cells may be caused by a number of factors. General categories of hypereosinophilia based on cause include the following:
- Primary hypereosinophilia is caused by cancers of the bone marrow or blood that directly increase the production of eosinophils.
- Secondary hypereosinophilia, also called reactive hypereosinophilia, is caused by conditions that typically activate white blood cells, such as:
- Parasitic or bacterial infections.
- Allergies.
- Immune system disorders.
- Long-lasting inflammatory diseases.
- Drug reactions.
- Familial hypereosinophilia is an inherited disorder.
- Idiopathic hypereosinophilia has no cause that can be found. Most cases are idiopathic.
Risk factors
HES can affect anyone, but it occurs more often in men.
June 27, 2025
- Roufosse F, et al. Hypereosinophilic syndromes: Clinical manifestations, pathophysiology, and diagnosis. https://www.uptodate.com/contents/search. Accessed Nov. 18, 2024.
- Ferri FF. Hypereosinophilic syndrome. In: Ferri's Clinical Advisor 2025. Elsevier; 2025. https://www.clinicalkey.com. Accessed Nov. 18, 2024.
- Hoffman R, et al. Eosinophilia, eosinophilic neoplasms, and the hypereosinophilic syndromes. In: Hematology: Basic Principles and Practice. 8th ed. Elsevier; 2023. https://www.clinicalkey.com. Accessed Nov. 18, 2024.
- Eosinophil production and function. Merck Manual Professional Version. https://www.merckmanuals.com/professional/hematology-and-oncology/eosinophilic-disorders/eosinophil-production-and-function. Accessed Nov. 22, 2024.
- Marra AM, et al. Eosinophil-associated diseases: The allergist's and clinical immunologist's perspective. European Annals of Allergy and Clinical Immunology. 2024; doi:10.23822/EurAnnACI.1764-1489.339.
- Rosenberg CE, et al. Diagnosis and management of pediatric hypereosinophilic syndrome. Journal of Allergy and Clinical Immunology: In Practice. 2022; doi:10.1016/j.jaip.2022.02.007.
- Roufosse F, et al. Hypereosinophilic syndromes: Treatment. https://www.uptodate.com/contents/search. Accessed Nov. 18, 2024.
- Klion AD. Approach to the patient with suspected hypereosinophilic syndrome. Hematology, American Society of Hematology Education Program. 2022; doi:10.1182/hematology.2022000367.
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Hypereosinophilic syndrome