Eosinophils are white blood cells that are part of the immune system

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Eosinophilia is an increased number of eosinophilic white blood cells. It is a sign of certain medical conditions, including allergies, asthma, infections, immune disorders, and some types of cancer. Eosinophilia can be associated with symptoms like a rash, swelling, or trouble breathing.

If you have eosinophilia, you might already have a known cause or need to undergo tests to identify the cause. Treatment is aimed at alleviating the underlying medical condition and reducing the effects of the excess eosinophils.

This article will discuss symptoms that can accompany eosinophilia, causes, treatment, tests that may be performed, and when to see a healthcare provider.

Eosinophilia can be part of an allergic reaction


Symptoms of Eosinophilia 

Eosinophils trigger an inflammatory reaction by releasing chemicals that directly destroy infectious organisms and signal other white blood cells and proteins to arrive at the site of infection. These actions are helpful when you have an infection. 

Some medical conditions cause excess eosinophils to circulate throughout the body or to accumulate in certain areas of the body, such as the skin, intestines, or lungs.

Eosinophilia often doesn't cause specific symptoms, especially during an infection. The symptoms you may experience with eosinophilia are usually the symptoms of the infection.

Sometimes eosinophilia causes symptoms that are related to the chemicals they release.

Symptoms can include: 

  • Swelling 
  • Rash 
  • Itching
  • Abdominal discomfort
  • Diarrhea
  • Congestion
  • Runny nose
  • Cough
  • Wheezing

Get Immediate Medical Help

Get immediate medical attention if your symptoms are progressing rapidly, if you are having trouble breathing, or if you have swelling of your mouth or throat.

Causes of Eosinophilia 

The most common causes of eosinophilia are asthma, allergies, parasitic infections, and certain medications. In these situations, the effects of eosinophilia are usually mild to moderate.

Common causes include:

  • Eosinophilic asthma: A type of adult-onset asthma in which lung inflammation is a prominent feature, common in people who have allergies
  • Aspergillosis: A fungal infection that usually affects the lungs
  • Chronic eosinophilic pneumonia: A type of pneumonia caused by recurrent or persistent eosinophils in the lungs
  • Eosinophilic esophagitis: A rare condition that causes trouble swallowing due to inflammation of the esophagus
  • Eosinophilic bronchitis: A type of bronchitis characterized by inflammation of the bronchi, without substantial bronchial narrowing
  • Drug allergies: A reaction to medications or supplements

Eosinophils are elevated in eosinophilic asthma, as well as asthma that is not specifically diagnosed as eosinophilic asthma.

Less common causes include:

  • Polyarteritis nodosa: An inflammatory disorder that affects arteries throughout the body
  • Lupus: An inflammatory condition that can affect many organs and tissues
  • Rheumatoid arthritis: An inflammatory disease that affects joints and other connective tissues throughout the body
  • Sarcoidosis: An inflammatory disease where clumps of cells accumulate in different areas of the body
  • Lymphoma: A type of white blood cell cancer
  • Acute or chronic graft versus host disease: A condition where transplanted tissue reacts against the body of the person who received the transplant
  • Idiopathic eosinophilia: A condition characterized by a high eosinophil count without an identifiable cause

Which Medications Can Cause Eosinophilia?

Some medications can cause varying degrees of elevations in eosinophils, and they may or may not cause associated symptoms. This medication side effect is not the same as an allergic reaction to the drug.

Medications that can cause high eosinophils include:

  • Non-steroidal anti-inflammatory medications
  • Penicillin, cephalosporins, Actzone (dapsone), sulfa-based antibiotics
  • Aloprim (allopurinol)
  • Tegretol (carbamazepine), Dilantin (phenytoin), Lamictal (lamotrigine), Depakote (valproate)
  • Viramune (nevirapine), Sustiva (efavirenz)

Your healthcare provider might not necessarily change your medication if your eosinophil count is only moderately elevated and if it isn't causing any bothersome symptoms or harmful effects.

How to Treat Eosinophilia 

Usually, if you have a high eosinophil count, the specific cause of eosinophilia is treated. For example, asthma is treated with medications that help prevent flare-ups and symptoms. Inflammatory diseases are often treated with immunosuppressants, and cancer is often treated with chemotherapy or other interventions, such as a bone marrow transplant.

And, in some situations, you might also need treatment to reduce your eosinophil count. Treatment of eosinophilia can include steroids, myelosuppressive medications, and immunomodulators. These treatments reduce inflammation.

There are also medications that can specifically target eosinophilia to reduce the effects of these white blood cells. These include the monoclonal antibodies, mepolizumab, reslizumab, and benralizumab.

Are There Tests to Diagnose the Cause of Eosinophilia?

Eosinophilia is diagnosed with a complete blood count (CBC). This test measures the number and percentage of different blood cells in a peripheral blood sample. 

If you have eosinophilia, your healthcare providers would also look at the numbers of your other blood cells, which can help point to the cause of your elevated eosinophil count. For example, you might have a high or low overall number of white blood cells along with your high eosinophil count.

The normal bone marrow and peripheral blood contains between 1% and 6% eosinophils, with an eosinophil count in the peripheral blood of 500 eosinophilic cells per microliter.

Eosinophilia is defined as an elevation of the eosinophil count above 500 cells per microliter.

Other tests you might need would be determined based on the most likely causes. 

For example:

  • If you have signs of an allergy, you might have allergy testing to identify the substance that you are allergic to. 
  • If you have had exposure to a parasitic infection, you might need tests to identify the specific type of parasite, such as a stool sample. 
  • If there is concern about blood cancer, you might have a bone marrow biopsy. 

Sometimes, a repeat eosinophil count is done to help determine whether the underlying condition is resolving.

When to See a Healthcare Provider

You would not know that you have eosinophilia or any other sign of a blood abnormality unless you have a blood test. 

You should see a healthcare provider if you begin to:

  • Have a fever 
  • Feel sick, run down, or excessively tired 
  • Notice a lump or swelling on your body 
  • Experience symptoms of an allergic reaction, such as coughing, wheezing, or a rash

Get urgent medical attention if you have swelling of your throat or mouth, or if you have trouble breathing. 


Eosinophilia is an increase in eosinophils, a type of white blood cell. These cells help the immune system fight infections. They can temporarily increase as an infection is resolving. Sometimes eosinophilia occurs due to medical conditions, such as allergies, asthma, inflammatory disorders, cancer, or as a medication side effect.

The symptoms of a high eosinophil count can include swelling, rashes, itching, wheezing and more. You may also have symptoms of the causative disease.

Eosinophilia is diagnosed with a complete blood count (CBC), and the cause is diagnosed with various specific tests. Treatment includes therapy for treating the underlying condition, and you might also need treatment to lower your eosinophil count.

A Word From Verywell

It can be concerning to see an elevated eosinophil count on a lab report. Your healthcare provider will interpret what it means by looking at other lab results along with your medical history and physical examination.

Don't hesitate to ask your healthcare provider to explain it to you. If you are having symptoms or if there's concern that your eosinophilia is part of an underlying medical issue, you may need further testing and a treatment plan.

Frequently Asked Questions

  • What symptoms might I feel with eosinophilia?

    Your symptoms will depend on the underlying condition causing eosinophilia. In an allergic reaction, you may have a rash, stuffy nose, wheezing, cough, and more.

  • Is eosinophilia a sign of COVID-19?

    Sometimes COVID-19 is associated with eosinophilia.

  • Can eosinophilia cause cancer?

    Eosinophilia can have many different causes, including some types of blood cancer, but eosinophilia does not cause cancer to develop. Blood cancers often result in an elevation in the number of one or more types of white blood cells.

8 Sources
Verywell Health uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read our editorial process to learn more about how we fact-check and keep our content accurate, reliable, and trustworthy.
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By Heidi Moawad, MD
Heidi Moawad is a neurologist and expert in the field of brain health and neurological disorders. Dr. Moawad regularly writes and edits health and career content for medical books and publications.