Eosinophilia happens when your body produces an unusually high number of eosinophils. Eosinophils are one of several white blood cells that support your immune system. Sometimes, certain medical conditions and medications cause high eosinophil levels.


What is eosinophilia?

Eosinophilia is an unusually high number of eosinophils in your blood (≥ [greater than or equal to] 500 eosinophils per microliter). Eosinophils are one of several white blood cells that support your immune system. They’re part of your body’s defense system against allergens and help protect your body from fungal and parasitic infections. Certain medical conditions and medications can cause high eosinophil counts.


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Is eosinophilia serious?

Depending on your eosinophil count, eosinophilia can be mild, moderate or severe. High eosinophil levels can indicate a mild condition such as a drug reaction or allergy, or a severe condition could cause it, including some blood disorders. Sometimes, high numbers of eosinophils crowd together at specific areas of your body, causing medical conditions linked to inflammation that can affect multiple areas of your body.

Symptoms and Causes

What causes eosinophilia?

Many conditions cause your eosinophil counts to increase in your blood. Some conditions, like seasonal allergies, asthma and reactions to medications are very common, and often aren’t very serious. Infections, especially from parasites, can also lead to eosinophilia. Problems with immune regulation can also cause eosinophilia, including autoimmune diseases like inflammatory bowel disease, autoimmune myocarditis, vasculitis and sarcoidosis. Blood cancers that make these cells inappropriately can also cause eosinophilia. Finally, genetic changes that are hereditary (passed on by your biological parents) can cause eosinophilia.


What can happen if eosinophil counts are high?

Sometimes, eosinophils cause inflammation in specific areas of your body. When this happens, it’s called an eosinophilic disorder or hypereosinophilia syndrome (HES). Specific eosinophilic disorders are named for the parts of your body that are affected. Eosinophilic disorders include:

  • Eosinophilic cystitis: This is a bladder disorder.
  • Eosinophilic fasciitis: This is a fascia disorder. Fascia is the connective tissue that runs throughout your body.
  • Eosinophilic pneumonia: This disorder affects your lungs.
  • Eosinophilic gastrointestinal disorders (EGID): EGID includes eosinophilic esophagitis, which affects your esophagus, as well as disorders that affect your colon (large intestine), stomach and small intestine.
  • Eosinophilic granulomatosis with polyangiitis (EGPA): This condition, also known as Churg-Strauss syndrome, affects your lungs, heart, sinuses and other organs.
  • Hypereosinophilic syndrome: This is a rare group of conditions linked to continuously high levels of eosinophilia. Hypereosinophilic syndrome typically affects your heart, central nervous system, skin and respiratory tract.

What are eosinophilia symptoms?

Eosinophilia doesn’t always cause symptoms. High eosinophil levels usually are from underlying conditions that cause many different symptoms.


Diagnosis and Tests

How do healthcare providers diagnose eosinophilia?

Healthcare providers typically discover eosinophilia during a routine blood test called a complete blood count (CBC) with a differential white blood cell count. Depending on your situation, your healthcare provider may do more tests to find out why your eosinophil levels are higher than normal.

Management and Treatment

How do healthcare providers treat eosinophilia?

Healthcare providers treat the underlying condition or issue that’s causing high eosinophil counts. For example, if you have eosinophilic esophagitis, your healthcare provider may prescribe steroids or other medications. If you have high eosinophil levels because you have allergies or chronic sinusitis, your healthcare provider may recommend allergy testing to find out what causes the allergic reaction that triggered eosinophilia. If a medication is causing eosinophilia, your healthcare provider will usually recommend stopping or avoiding it. If there’s an infection, your healthcare provider will treat it. If there’s a blood cancer, your healthcare provider will treat it.


How can I prevent eosinophilia?

Allergies are the most common cause of high eosinophil levels. You can prevent allergy-related eosinophilia with treatment to control your body’s allergic reactions. But there are times when eosinophilia may be a sign of an underlying condition that you may not be able to prevent.

Outlook / Prognosis

What can I expect if I have eosinophilia?

If you have high eosinophils levels, you may need treatment for the underlying condition causing your high levels. There are many causes, ranging from mild and completely safe to more serious. Talk to your healthcare provider to learn more.

A note from Cleveland Clinic

Eosinophilia happens when your body produces too many eosinophils. Eosinophils are one of several white blood cells that support your immune system. Many times, people learn they have eosinophilia when they have routine blood tests. A high eosinophil count typically isn’t a cause for alarm. Your healthcare provider may order additional tests to find out why your eosinophil levels are unusually high.

Medically Reviewed

Last reviewed on 05/12/2022.

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