July 21, 2020

What is Eosinophils?

Eosinophils are a type of white blood cell (leucocyte). They make up approximately 1-3% of a healthy individuals blood count.[1] Eosinophils are made in the bone marrow and contribute to the immune system, helping to fight off infection. Like basophils, eosinophils contain granules, making them a granulocyte. The granules contain substances designed to fight infections. Eosinophils, as well as basophils and mast cells, are also responsible for the mechanisms associated with the allergic response of the body.

Why take an Eosinophils blood test?

Because eosinophils are a part of the immune system, they are a good biomarker for infection. For example, an increased number of eosinophils in the blood is indicative of an invading pathogen which the body is trying to kill to prevent illness.

An increase in eosinophil numbers can indicate several diseases, commonly allergic types such as asthma, helminth worm infections or drug reactions.[2] An eosinophil blood test will measure the number of eosinophils in your blood and identifies the presence of allergic disease.

You can check your level of eosinophils together with other white blood cells within Forth’s Vitality and Ultimate blood tests.

What function does Eosinophils have in the body?

Eosinophils are good markers of infection or allergy. If the body is already fighting an infection, it is common for other infections to invade such as coughs and colds.

The functions of eosinophils are multifaceted. Their roles include:

  • Presentation of antigens
  • Release of mediators for acute and chronic inflammation
  • Degranulation upon the presentation of helminth worms or parasites[3]

Eosinophils cause tissue damage and inflammation in many diseases including asthma. They work alongside other immune cells including basophils and mast cells, all of which are important mediators in allergic responses.

How do changes in Eosinophils affect health and wellbeing?

Allergies such as asthma can affect your everyday life, particularly at certain times of the year. For example, if you are allergic to grass pollen, your symptoms may be more prevalent during June and July. Eosinophil numbers increase during a parasitic infection or allergy.

If an increased eosinophil count is because of a parasitic or worm infection, then the symptoms can make you feel quite unwell. Plus, an infection can cause a reduction in energy levels, making you feel weak and tired.

If you are worried about your immune system or just want to check where you fall on the range, you can test your eosinophils level with a simple at-home blood test.

What can cause Eosinophils to change?

There are several allergic diseases which are associated with increased eosinophil numbers. For example, allergic rhinitis, atopic asthma and atopic dermatitis all increase the number of eosinophils present in the blood. Allergies occur when the body’s immune system identifies a substance as if it is harmful. For example, an individual who is sensitive to outdoor allergens such as grass pollen may have an asthmatic reaction. When the substance responsible for the reaction enters the body, eosinophils alongside basophils and mast cells, are released. Once activated, their purpose is to help rid the body of the invading pathogen.

Eosinophils are unique granulocytes in that they can survive in the body for a prolonged period despite only having a short half-life within the blood of 8-18 hours.[4]

Eosinophil numbers also increase in the presence of some parasites, like helminth worms.


What are the most common symptoms?

An increase in the numbers of eosinophils is typical of atopic asthma. Symptoms of atopic asthma are:

  • Wheezing which sounds like whistling when breathing
  • Breathlessness
  • Coughing
  • A tight chest like a band tightening around it

A severe asthma attack may cause the following symptoms:

  • Severe and constant wheezing, coughing and chest tightness
  • Breathlessness so severe that you are unable to speak, eat or sleep
  • Fast heartbeat
  • Breathing faster
  • Blue lips or fingers
  • Drowsiness, confusion, exhaustion or dizziness
  • Fainting[5]

Common symptoms of a parasitic infection are:

  • Diarrhoea
  • Vomiting
  • Fever
  • Skin Rashes
  • Coughing

How to keep Eosinophils in the healthy range

Eosinophils are an important part of the immune system. They work alongside other granulocytes to help fight infection. They are also key mediators in the allergic response of the body. Although you may not be able to directly influence your eosinophil count, there are some steps you can take to keep your immune system healthy.

Nutrition is an important aspect of our immune status and deficiency in some nutrients can weaken the system. It is essential to eat a healthy, balanced diet incorporating the following macronutrients:

  • zinc
  • selenium
  • iron
  • copper
  • vitamins a, c, e and b6
  • folic acid[6]

Smoking has also been implicated in damaging the immune system. Therefore, it is important to stop smoking if you currently do, particularly as the damage is reversible if you quit.[7]

Exercise is key to a healthy lifestyle. However, participating in intense exercising can cause immunodepression during recovery. One exercise bout has the ability to change the white blood cell composition and this can remain changed even during recovery. Therefore, it is essential to have enough rest between exercise sessions to prevent illness and injury.[8]


[1] Lab Tests Online. (2017). Eosinophil. Available at: https://labtestsonline.org.uk/glossary/eosinophil

[2] Stone, K, D et al. (2009). IgE, Mast Cells, Basophils and Eosinophils. J Allergy Clin Immunol.

[3] Kovalszki, A and Weller, P, F. (2016). Eosinophilia. Prim Care: 43(4), pp 43(4).

[4] Mean Park, Y and Bochner, B, S. (2010). Eosinophil Survival and Apoptosis in Health and Disease. Allergy Asthma Immunol Res: 2(2), pp 87-101.

[5] NHS. (2018). Symptoms Asthma. Available at: https://www.nhs.uk/conditions/asthma/symptoms/

[6] ChandraRK (1997). Nutrition and the Immune System: An Introduction. American Journal of Clinical Nutrition: 66, pp 460S-463S

[7] Davis, M, M. (2017). Human Immune System Variation. Nature Reviews: Immunology: 17(1), pp 21-29.

[8] Peake, J, M., Neubauer, O., Walsh, N, P and Simpson, R, J. (2016). Recovery of the Immune System After Exercise. Journal of Applied Physiology: 122, pp 1077-187.

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This information has been medically reviewed by Dr Nicky Keay

Nicola has extensive clinical and research experience in the fields of endocrinology and sport and exercise medicine. Nicky is a member of the Royal College of Physicians, Honorary Fellow in the Department of Sport and Exercise Sciences at Durham University and former Research Fellow at St. Thomas' Hospital.

Dr Nicky Keay

Dr Nicky Keay

BA, MA (Cantab), MB, BChir, MRCP.