Eosinophils on a blood test: what high eosinophils (eosinophilia) mean
Eosinophils (absolute eosinophil count) (EOS / AEC) · CBC with differential · reported in ×10³/µL (same as ×10⁹/L or cells/µL ÷ 1000); also reported as % of white blood cells
Eosinophils are white blood cells that specialise in fighting parasites and in driving allergic inflammation, releasing granules packed with proteins that damage worms and, when misdirected, the lining of the airways, gut and skin. On an adult CBC with differential, most US labs call an absolute eosinophil count of 0–0.5 ×10³/µL (0–500 cells per microlitre), or about 0–6% of white cells, normal. The two most common reasons the count is high are allergic disease (asthma, hay fever, eczema) and a reaction to a medication; worldwide, parasitic infection is the leading cause, and in travellers and immigrants it should always be considered.
Most high eosinophil results are mild (0.5–1.5 ×10³/µL), come with an obvious allergic explanation and need no action beyond treating the allergy. The count becomes clinically important above 1.5 ×10³/µL (hypereosinophilia), because at sustained levels eosinophils can infiltrate and damage the heart, lungs, nerves and skin whatever the cause. A persistently very high count with no explanation is what justifies a specialist work-up for the rare hypereosinophilic syndromes.
This page explains how the number is derived, what the percentage and absolute count each tell you, the grades of eosinophilia and what each means, the real causes in order of how often they turn up, which markers a clinician reads it beside, and the diet and lifestyle levers with human evidence.
EOS / AEC at a glance
- Eosinophils are white blood cells that attack parasites and drive allergic inflammation; they make up a small share of white cells.
- Normal adult absolute eosinophil count: under 0.5 ×10³/µL (under 500/µL), about 0–6% of white cells; the count is lowest in the morning and highest at night.
- Mild eosinophilia (0.5–1.5 ×10³/µL) most often means allergy, asthma, eczema or a drug reaction; parasites are the leading cause worldwide.
- Hypereosinophilia (above 1.5 ×10³/µL on two tests a month apart) needs a work-up because sustained high counts can damage the heart and other organs.
- A low eosinophil count (0) is normal and usually reflects steroids, stress or acute infection rather than a disease.
- Next step: review allergies, medications and travel; repeat the count; if it stays above 1.5, expect stool tests, IgE, cortisol, a blood film and often a referral.
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What EOS / AEC measures
The eosinophil result is part of the white cell differential on a complete blood count. Automated analysers identify eosinophils by their large, bright granules and report them as a percentage of white cells and as an absolute eosinophil count (AEC), the percentage multiplied by the total white cell count. Because the normal count is small, a percentage of 8% can be a normal 0.4 ×10³/µL when the white count is low or an abnormal 1.0 ×10³/µL when it is high. Only the absolute count should be interpreted.
Eosinophils spend only a few hours in the blood before entering tissues, especially the gut lining, lungs and skin, where they live for days to weeks. The blood count is therefore a window on a much larger tissue population and can underestimate tissue eosinophilia: eosinophilic oesophagitis, for example, often has a normal blood count. Counts also follow a daily rhythm driven by cortisol, lowest in the late morning and highest around midnight, so the time of a draw can shift a borderline result.
Normal range for EOS / AEC
Reference ranges vary between labs and by age, sex and pregnancy. Use the range printed on your own report.
| Group | Typical range (×10³/µL (same as ×10⁹/L or cells/µL ÷ 1000); also reported as % of white blood cells) | Notes |
|---|---|---|
| Adults, absolute count | 0.0–0.5 ×10³/µL (0–500 cells/µL) | Some labs use 0.05–0.5 or 0–0.45. Eosinophilia is defined as above 0.5 ×10³/µL. |
| Adults, percentage | 0–6% of white blood cells | 1–4% is typical. Always use the absolute count. |
| Children | 0.0–0.7 ×10³/µL | Slightly higher in young children; mild rises with eczema and hay fever are common. |
| Pregnancy | Similar or slightly lower | Eosinophils fall during labour and immediately after delivery. |
| Mild eosinophilia | 0.5–1.5 ×10³/µL | Usually allergy, asthma, eczema or a drug. |
| Moderate eosinophilia (hypereosinophilia) | 1.5–5.0 ×10³/µL | Needs a cause found; organ damage becomes possible if sustained. |
| Severe eosinophilia | Above 5.0 ×10³/µL | Prompt specialist evaluation. |
High eosinophils (eosinophilia)
A high eosinophil count means the body is producing more eosinophils, almost always in response to the cytokine IL-5 released during allergic reactions, parasitic infection or certain drug reactions. Mild eosinophilia (0.5–1.5 ×10³/µL) with hay fever, asthma, eczema or a recently started medication is expected and not harmful in itself; the count falls when the allergy is controlled or the drug stopped.
Counts above 1.5 ×10³/µL that persist on two tests at least a month apart are called hypereosinophilia and need a cause found, because eosinophils at these levels can infiltrate the heart (eosinophilic myocarditis and endomyocardial fibrosis), lungs, skin, gut and nerves regardless of why they are raised. If no secondary cause is found and there is evidence of organ involvement, the diagnosis is hypereosinophilic syndrome (HES), a rare group of disorders, some driven by a treatable gene rearrangement (FIP1L1-PDGFRA) that responds to imatinib. Most people with a high count never reach this territory.
Common causes
Allergic disease: asthma, allergic rhinitis, eczema
The most common cause in the US. IL-5 from activated T cells raises eosinophil production; counts are typically 0.5–1.0 ×10³/µL and track with symptoms and pollen seasons. Eosinophilic asthma is now a treatment category with its own biologic drugs.
Drug reactions
Antibiotics (penicillins, cephalosporins, sulfonamides), allopurinol, anticonvulsants (carbamazepine, phenytoin, lamotrigine), NSAIDs and many others can raise eosinophils, with or without a rash. Eosinophilia with fever, rash and liver involvement two to eight weeks after a new drug is DRESS syndrome, a medical emergency.
Parasitic infection
Tissue-invading helminths such as Strongyloides, hookworm, Toxocara, filaria, schistosomes and Ascaris are the leading cause worldwide and in anyone who has lived in or travelled to endemic areas. Strongyloides matters most because it can persist for decades and become life-threatening if steroids are later given. Protozoa (Giardia, amoebae) do not usually raise eosinophils.
Eosinophilic gastrointestinal disorders
Eosinophilic oesophagitis, gastritis and colitis cause food to stick, reflux-like symptoms, pain or diarrhoea; the blood count is often normal or only mildly raised because the eosinophils are in the gut wall.
Skin diseases
Atopic dermatitis, urticaria, bullous pemphigoid and scabies all cause mild to moderate eosinophilia.
Adrenal insufficiency (Addison disease)
Cortisol normally suppresses eosinophils, so a loss of cortisol lets the count rise. Eosinophilia with fatigue, low blood pressure, salt craving or low sodium should prompt a morning cortisol.
Autoimmune and inflammatory conditions
Eosinophilic granulomatosis with polyangiitis (EGPA, formerly Churg-Strauss) combines asthma, high eosinophils and vasculitis. Inflammatory bowel disease, sarcoidosis and some connective tissue diseases cause milder rises.
Lymphoma and other cancers
Hodgkin lymphoma and T-cell lymphomas release IL-5 and cause reactive eosinophilia; some solid tumours do too. Persistent eosinophilia with enlarged nodes, sweats or weight loss should be investigated.
Hypereosinophilic syndromes and eosinophilic leukaemia
Rare primary marrow disorders in which eosinophils are produced autonomously, often with counts above 5 ×10³/µL and organ damage. Tests include FIP1L1-PDGFRA and other gene rearrangements, tryptase, B12 and a marrow biopsy.
Lab timing
Counts peak around midnight and are lowest in the late morning; an evening draw can read 20–40% higher than a morning one. Recent stopping of steroids also causes a rebound rise.
Symptoms that can go with it
- Often none; the count is found incidentally
- Sneezing, itchy eyes, wheeze or cough in allergic disease and asthma
- Itchy rash, hives or eczema flares
- Fever, widespread rash and swollen glands after a new drug (DRESS syndrome: seek care urgently)
- Abdominal pain, diarrhoea, food sticking or weight loss in parasitic or eosinophilic gut disease
- Breathlessness, chest pain, palpitations, numbness or weakness with very high counts, which can signal heart or nerve involvement
Low eosinophils (eosinopenia)
A low or absent eosinophil count is usually normal and carries little clinical weight on its own, because the healthy range starts at zero. When it is noted, it most often reflects cortisol: either a steroid medication or the body's own stress response to acute infection, surgery or injury, which drives eosinophils out of the blood within hours. Eosinopenia during a febrile illness is in fact a well-studied marker pointing toward bacterial infection or sepsis rather than a viral one.
The result only becomes diagnostically useful when the clinical question is adrenal function (a normal or high eosinophil count in a critically ill patient on no steroids can hint at adrenal insufficiency) or when a previously raised count is being tracked on treatment.
Common causes
Corticosteroid medication
Prednisone, dexamethasone and high-dose inhaled or injected steroids reduce eosinophils to near zero within hours, which is partly how they work in asthma and allergy.
Acute infection, sepsis or physical stress
The surge of cortisol and adrenaline in acute bacterial infection, surgery, trauma or burns clears eosinophils from the blood. A count of zero in someone with fever makes bacterial infection more likely.
Cushing syndrome
Chronic excess cortisol from any source suppresses eosinophils persistently.
Time of day
Eosinophils are lowest in the late morning when cortisol peaks; a morning draw in someone with a borderline count can read as zero.
Alcohol intoxication
Heavy acute alcohol intake transiently lowers eosinophils.
Symptoms that can go with it
- None attributable to the low count itself
- Fever, chills or feeling acutely unwell when it reflects bacterial infection
- Weight gain, round face, easy bruising and high blood pressure if Cushing syndrome is the cause
Read it alongside
- Total white blood cell count — the absolute eosinophil count is percentage × WBC; interpret only the absolute number.
- Neutrophils — neutrophilia with eosinophilia suggests a drug reaction or inflammatory disease; isolated eosinophilia with a normal neutrophil count favours allergy or parasites.
- Basophils — raised together with eosinophils points to a myeloproliferative disorder or chronic myeloid leukaemia rather than allergy.
- Total IgE — high in allergic disease and in many parasitic infections; it supports an allergic cause but does not rule out parasites.
- Blood film — confirms the count, shows whether eosinophils look normal, and detects immature cells or blasts in primary marrow disorders.
- Morning cortisol — rules out adrenal insufficiency when eosinophilia comes with fatigue, weight loss or low sodium.
- Troponin and ECG — checked in hypereosinophilia because the heart is the organ most at risk from sustained high counts.
What usually happens next
- Go through every medication and supplement started in the past three months; stopping a culprit drug (with your prescriber) usually normalises the count within weeks.
- Tell your clinician about hay fever, asthma, eczema, hives, travel to or residence in tropical or subtropical regions, raw or undercooked food, and gut or skin symptoms.
- Repeat the CBC in 4–6 weeks, ideally at the same time of day; mild eosinophilia that resolves needs no further work.
- If the count stays above 0.5 ×10³/µL with no clear cause, or is above 1.5 at any point, expect stool examinations for ova and parasites (three samples), Strongyloides serology, IgE, cortisol, liver and kidney tests, a blood film and chest X-ray.
- Counts above 1.5 ×10³/µL that persist, or any count with chest, heart, nerve or skin symptoms, go to haematology or allergy-immunology, where tests for FIP1L1-PDGFRA, tryptase and lymphocyte subsets are considered.
- If steroids are ever planned and you have lived in an endemic region, ask for Strongyloides testing first; steroids can turn a silent infection into a dangerous one.
Diet, lifestyle and natural levers with evidence
What can move EOS / AEC once the cause is known. Nothing here replaces finding the cause.
Identify and avoid the allergen or trigger food
Strong evidenceIn adults with eosinophilic oesophagitis, a six-food elimination diet (dairy, wheat, egg, soy, nuts, seafood) produced histological remission in about 70% in a prospective trial, with reintroduction identifying the culprit food in most. For airway and skin allergy, allergen avoidance and treatment lower blood eosinophils in step with symptoms. Elimination diets work best with a dietitian and a plan to reintroduce foods.
Do not remove whole food groups long term without supervision; nutritional gaps and disordered eating are real risks.
Weight loss in overweight asthma
Moderate evidenceA 10-week randomised trial of dietary restriction, exercise or both in overweight and obese adults with asthma found that weight loss of 5–10% improved asthma control and reduced sputum eosinophils, with diet-induced loss showing the clearest effect on airway eosinophilic inflammation.
Vitamin D repletion in asthma
Moderate evidenceA Cochrane review of randomised trials found that vitamin D supplementation reduced the rate of asthma attacks needing steroids by roughly 35–40% in people with mild to moderate asthma, with the benefit largely in those who started with low levels. Effects on the blood eosinophil count itself are inconsistent; the lever is fewer flares, not a lower number.
Test and correct a deficiency rather than taking high doses blindly; above 4,000 IU/day needs monitoring.
Omega-3 fatty acids
Preliminary evidenceTrials of fish oil in asthma and allergic disease are mixed: some show modest reductions in airway inflammation and exercise-induced bronchoconstriction, others no benefit. A few small studies reported lower blood or sputum eosinophils with 3–4 g/day of EPA+DHA, but larger trials have not confirmed a reliable effect.
High doses increase bleeding tendency with anticoagulants.
Quercetin and other flavonoids
Preliminary evidenceQuercetin stabilises mast cells and reduces eosinophil recruitment in laboratory and animal models, and small human trials in allergic rhinitis have shown modest symptom improvement. No trial has shown it lowers the blood eosinophil count, so it should be seen as a possible adjunct for allergy symptoms, not a treatment for eosinophilia.
Can interact with some blood thinners and antibiotics; avoid high doses in pregnancy and kidney disease.
Food hygiene and footwear in endemic regions
Strong evidenceHookworm and Strongyloides enter through bare skin on contaminated soil; Ascaris and Toxocara through contaminated food and hands. Wearing shoes, washing produce, hand washing and avoiding raw freshwater fish and undercooked meat prevent the parasitic infections that are the leading global cause of eosinophilia. Existing infection needs antiparasitic medication, not diet.
When to see a clinician promptly
- An absolute eosinophil count above 1.5 ×10³/µL on any test, or above 0.5 that persists on repeat with no explanation.
- Eosinophilia with fever, widespread rash, facial swelling or swollen glands two to eight weeks after starting a new drug: this can be DRESS syndrome and needs same-day care.
- Chest pain, breathlessness, palpitations, numbness, weakness or new skin lesions alongside a high count, which can signal organ involvement.
- Unexplained weight loss, night sweats, enlarged lymph nodes or persistent diarrhoea with eosinophilia.
- Any eosinophilia in someone who has lived in or travelled to tropical regions, before any course of steroids is started.
Frequently asked questions
Is an eosinophil count of 0.6 bad?
A count of 0.6 ×10³/µL (600/µL) is mildly high and, in someone with hay fever, asthma or eczema, is expected and not harmful. It usually settles when the allergy is controlled. If you have no allergic condition, the useful steps are a medication review, a travel and symptom history and a repeat test in a month or two.
What is the most common cause of high eosinophils?
In the US and Europe, allergic disease (asthma, allergic rhinitis, atopic dermatitis) and drug reactions account for most cases. Worldwide, parasitic worm infection is the leading cause and should be considered in anyone with relevant travel or residence, even decades earlier, because some parasites such as Strongyloides persist for life.
Can stress or anxiety raise eosinophils?
No, the opposite. Stress raises cortisol, which lowers eosinophils. A high eosinophil count is not explained by anxiety. Counts do rise overnight as cortisol falls, so an evening blood draw can read higher than a morning one.
What cancers cause high eosinophils?
Hodgkin lymphoma and some T-cell lymphomas are the classic ones, because the tumour cells release IL-5. Chronic myeloid leukaemia and other myeloproliferative disorders can raise eosinophils alongside other cells, and chronic eosinophilic leukaemia is a rare primary cause. Some solid tumours of the lung, gut and cervix occasionally cause reactive eosinophilia. Cancer is an uncommon explanation overall.
Does eosinophilia mean I have parasites?
Not necessarily, but it should be considered. Worms that invade tissue (hookworm, Strongyloides, Toxocara, filaria, schistosomes) cause eosinophilia; gut-confined protozoa such as Giardia usually do not. If you have ever lived in or travelled to an endemic region, stool tests and Strongyloides blood serology are standard, because treatment is simple and missing it before steroids can be dangerous.
Can eosinophils be high with no symptoms?
Yes, often. Many people with mild allergy, a recently started medication or a quiet parasitic infection feel entirely well. That is why persistent unexplained eosinophilia is investigated even without symptoms, and why sustained counts above 1.5 ×10³/µL prompt checks of the heart and lungs: damage can begin before anything is felt.
What does eosinophilia with low cortisol mean?
Cortisol suppresses eosinophils, so a high eosinophil count with fatigue, weight loss, dizziness on standing, salt craving or low sodium raises the possibility of adrenal insufficiency (Addison disease). A morning cortisol and, if needed, an ACTH stimulation test confirm or exclude it. It is uncommon but important, because it is readily treatable.
How quickly do eosinophils come down after stopping a drug?
Usually within two to six weeks of stopping the culprit medication, although in DRESS syndrome the count and symptoms can take months to settle and sometimes need steroids. If the count is still raised two months after a suspected drug is stopped, the drug was probably not the cause and other explanations should be looked for.
References
- Blood differential test. MedlinePlus, US National Library of MedicineView source
- Eosinophilia. Mayo ClinicView source
- Eosinophilia. Merck Manual Professional VersionView source
- Roufosse F, Weller PF. Practical approach to the patient with hypereosinophilia. Journal of Allergy and Clinical Immunology (2010)
- Valent P, Klion AD, Horny HP, et al.. Contemporary consensus proposal on criteria and classification of eosinophilic disorders and related syndromes. Journal of Allergy and Clinical Immunology (2012)
- Gonsalves N, Yang GY, Doerfler B, Ritz S, Ditto AM, Hirano I. Elimination diet effectively treats eosinophilic esophagitis in adults; food reintroduction identifies causative factors. Gastroenterology (2012)
- Scott HA, Gibson PG, Garg ML, et al.. Dietary restriction and exercise improve airway inflammation and clinical outcomes in overweight and obese asthma: a randomized trial. Clinical and Experimental Allergy (2013)
- Martineau AR, Cates CJ, Urashima M, et al.. Vitamin D for the management of asthma. Cochrane Database of Systematic Reviews (2016)
- Riley LK, Rupert J. Evaluation of patients with leukocytosis. American Family Physician (2015)View source
- Vitamin D: fact sheet for health professionals. NIH Office of Dietary SupplementsView source
- Omega-3 fatty acids: fact sheet for health professionals. NIH Office of Dietary SupplementsView source
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