What is Eosinophilia?


Eosinophilia is a medical term to describe a condition in which the body produces more eosinophils (a type of white blood cell) than is typical. Eosinophils are a component of your immune system and help defend your body against parasites, certain infections, and allergies.1,2 

Continue reading to discover more about the potential causes, symptoms, and treatment options for eosinophilia. Understanding eosinophilia can improve your ability to better recognise its signs, and if needed, seek appropriate medical care.

What are eosinophils?

Eosinophils are a type of white blood cell that are very important in the immune system. They are named after the staining characteristic of their granules (cell ‘pockets’ containing toxic proteins), which turn a reddish-pink colour whenever exposed to a dye called eosin. Eosinophils are produced in the bone marrow and circulate in the bloodstream, although they can be found in tissues.3

Their primary function is to protect the body from parasitic infections, especially those related to helminths, also known as worms, and certain protozoa by releasing toxic substances to destroy these parasites, limiting their spread. 

They also contribute to allergic reactions and asthma, as eosinophils are recruited to the affected area when our immune system encounters an allergen. Moreover, eosinophils are capable of influencing other immune cells through the production of substances and contributing to the immune balance.3,4

Although they are normally in low levels in the bloodstream, some disorders or infections can cause an increased eosinophil count, leading to eosinophilia. Properly monitoring eosinophil  levels can provide important diagnostic information and help doctors choose appropriate treatments.

Causes of eosinophilia

Eosinophilia is characterised by elevated levels of eosinophils, either in the blood or in tissues, and it can occur due to various causes. Usually, it can happen due to an underlying condition, as the most common include:

  • Allergic reactions: allergies to certain substances, such as foods, medications, insect bites or stings, and environmental allergens
  • Parasitic infections: caused by parasites like helminths or certain protozoa
  • Medications: antibiotics, allopurinol, sulfasalazine, some anticonvulsants, and anti-retroviral agents can trigger eosinophilia as an adverse drug reaction
  • Blood diseases: hypereosinophilic syndrome and eosinophilic leukaemia, are characterised by persistent eosinophilia
  • Solid tumours: including certain types of gastrointestinal, lung, and genitourinary cancers
  • Other conditions, including:
  • Unknown causes: when the cause of eosinophilia remains unclear, it is classified as idiopathic eosinophilia3,5,6

Signs and symptoms of eosinophilia

The signs and symptoms of eosinophilia depend on the underlying cause and which organs are damaged because eosinophilia is typically a symptom of a number of illnesses. Eosinophilia can occasionally go unnoticed, discovered only by standard blood tests. 

Because it can be caused by a variety of diseases, the symptoms are diverse, affecting organ systems such as the skin, the lungs, the gastrointestinal tract and the cardiovascular system. 

Symptoms may include:

  • Coughing
  • Dyspnea (shortness of breath)
  • Myalgia: muscle pain
  • Angioedema: swelling in the deeper layers of the skin
  • Rashes
  • Rhinitis
  • Pruritus: itchy skin
  • Fever
  • Night sweats
  • Exhaustion
  • Weight loss2,7

Eosinophilia can occasionally result in swelling of the spleen and lymph nodes. There may also be additional symptoms related to the illnesses that cause eosinophilia, but are not a direct result of eosinophilia itself.1,3

Management and treatment for eosinophilia

The underlying cause and the severity of the symptoms determine how to manage and treat eosinophilia. Eosinophilia treatment plans should be specific to each patient's needs and health. Consult a healthcare provider for an accurate diagnosis, proper therapy, and continuous management of eosinophilia.

A doctor may prescribe corticosteroids to reduce inflammation and suppress the immune system, or antihistamines or leukotriene inhibitors to moderate allergic reactions. It may also be necessary to take medicine that helps control eosinophil levels, like interleukin-5 antagonist monoclonal antibodies, depending on the severity of the eosinophilia. 

Additionally, avoiding certain triggers like allergens might lessen eosinophilic reactions. Having regular follow-ups to check on eosinophil levels can also help to lessen eosinophilia.1,8


To help determine the best course of action for care and treatment, the diagnosis focuses on figuring out what is causing the eosinophilia. Depending on the unique conditions and suspected underlying cause, the specific diagnostic procedure may change. Therefore, it is essential to seek medical advice to get an accurate diagnosis and a personalised treatment plan.

The diagnosis of eosinophilia can be done with a combination of a medical history assessment, a physical exam, and blood tests such as a complete blood count, which gives information about the different cells present in your blood, like eosinophils. 

Other exams may be requested according to the clinical history presented, including:

  • Serum tryptase
  • Vitamin B12
  • Specific immunoglobulins (antibodies)
  • Stool test
  • Imaging and ultrasound exams
  • Tests to check cardiac and pulmonary functions3,9

Sometimes, according to the suspected cause and symptoms, your healthcare provider may refer you to specialists such as haematologists, pulmonologists, allergists, or gastroenterologists for further evaluation.3,9


How can I prevent eosinophilia?

Preventing eosinophilia involves addressing its underlying causes. To reduce the risk or manage its associated conditions, it is important to take steps such as allergy management, infection prevention, medication awareness, regular check-ups, a healthy lifestyle, and following your healthcare provider's recommendations. Consultation with a healthcare professional is recommended to assess your specific situation and receive personalised advice on prevention and management strategies.3

How common is eosinophilia?

The prevalence of eosinophilia varies depending on the underlying cause and population being studied. Although eosinophilia may be common, underlying diseases such as autoimmune disorders, cancers, and parasitic infections will also affect the prevalence of eosinophilia.

Who is at risk of eosinophilia?

Eosinophilia is a condition that can occur in individuals of any age, gender, or ethnic background. Risk factors for developing eosinophilia include allergies, parasitic infections, autoimmune conditions, medications, environmental exposures, and rare blood disorders.

When should I see a doctor?

It is important to consult a healthcare professional if you have any concerns or symptoms related to eosinophilia. These include elevated eosinophil count, persistent or recurring symptoms, allergic reactions, suspected underlying conditions, questions about monitoring and management, and unexplained symptoms.


Eosinophilia is a condition characterised by an elevated number of eosinophils, a type of white blood cell, in the blood or tissues. 

It can occur due to various underlying causes, such as: 

  • Allergic reactions 
  • Parasitic infections 
  • Asthma 
  • Autoimmune diseases 
  • Medications 
  • Skin disorders 
  • Connective tissue diseases 
  • Blood disorders 
  • Solid tumours 
  • Unknown causes (idiopathic eosinophilia) 

Symptoms and management of eosinophilia can vary depending on the underlying cause and the  affected organs or systems. Management and treatment also depend on the severity of the symptoms. 

Diagnosis involves assessing medical history, conducting a physical examination, and performing laboratory tests. Consultation with specialists may also be required for further evaluation and management.


  1. Ramirez GA, Yacoub MR, Ripa M, Mannina D, Cariddi A, Saporiti N, et al. Eosinophils from Physiology to Disease: A Comprehensive Review. Biomed Res Int. 2018 Jan 28;2018:9095275. Available from: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5829361/ 
  2. Shomali W, Gotlib J. World Health Organization-defined eosinophilic disorders: 2022 update on diagnosis, risk stratification, and management. American Journal of Hematology. 2022;97(1):129–48. Available from: https://onlinelibrary.wiley.com/doi/abs/10.1002/ajh.26352 
  3. Kuang FL. Approach to the patient with eosinophilia. Med Clin North Am. 2020 Jan;104(1):1–14. Available from: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC7089574/ 
  4. Wen T, Rothenberg ME. The Regulatory Function of Eosinophils. Microbiol Spectr. 2016 Oct;4(5):10.1128/microbiolspec.MCHD-0020–2015. Available from: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5088784/ 
  5. Leverone N, Tran S, Barry J, Akuthota P. Diagnoses associated with peripheral blood eosinophilia: A 5-year review. Annals of Allergy, Asthma & Immunology. 2021 Nov 1;127(5):597–8. Available from: https://www.annallergy.org/article/S1081-1206(21)00571-8/fulltext 
  6. Kovalszki A, Weller PF. Eosinophilia. Primary Care: Clinics in Office Practice. 2016 Dec 1;43(4):607–17. Available from: https://www.sciencedirect.com/science/article/pii/S0095454316300501 
  7. Butt NM, Lambert J, Ali S, Beer PA, Cross NCP, Duncombe A, et al. Guideline for the investigation and management of eosinophilia. British Journal of Haematology. 2017;176(4):553–72. Available from: https://onlinelibrary.wiley.com/doi/abs/10.1111/bjh.14488 
  8. Olaguibel J, Sastre J, Rodríguez J, Del Pozo V. Eosinophilia Induced by Blocking the IL-4/IL-13 Pathway: Potential Mechanisms and Clinical Outcomes. J Investig Allergol Clin Immunol. 2022 Jun 15;32(3):165–80. Available from: http://www.jiaci.org/summary/vol32-issue3-num2501 
  9. Naymagon L, Marcellino B, Mascarenhas J. Eosinophilia in acute myeloid leukemia: Overlooked and underexamined. Blood Reviews. 2019 Jul 1;36:23–31. Available from: https://www.sciencedirect.com/science/article/pii/S0268960X18301188 
This content is purely informational and isn’t medical guidance. It shouldn’t replace professional medical counsel. Always consult your physician regarding treatment risks and benefits. See our editorial standards for more details.

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Inês Dias

Master's Degree, Molecular Biology and Genetics, Faculty of Sciences, University of Lisbon

Inês is a scientist in the field of Biomedical Sciences, with a wealth of experience in various laboratory procedures. Her expertise is evident in her work as clinical analysis technician, performing puncture procedures for the collection of biological samples. She has also played a key role in COVID-19 sample processing in a laboratory setting. Recently obtained her master’s in Molecular Biology and Genetics from the Faculty of Sciences at the University of Lisbon.

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