People go to their doctor to get their eosinophils tested as part of a standard panel. Almost always, the results are not scrutinized, even though we know that you can be healthier and live longer when your results lie within optimal ranges. When I used to go to doctors and tried to discuss my results, they had no clue what these meant from a health perspective. All they cared about was whether they could diagnose me with some disease.
Read on to learn more about eosinophils, their roles in our health and disease, and how to lower their levels.
What are Eosinophils?
Eosinophils are a kind of white blood cell produced by the bone marrow. They are usually found in the gut, lungs, thymus, breast glands, and uterus. They are only in the blood for short periods of time [1, 2, 3].
When activated, eosinophils move into the affected tissue and secrete inflammatory substances that help destroy the foreign organism. Sometimes, the eosinophils can also cause damage to our tissues .
Eosinophils Help Balance the Immune System
Eosinophils are important for our health since they help keep the immune system balanced. They help control the response to foreign antigens, from both food and microorganisms (harmful and from the microbiota) in the intestines [2, 5].
Right after birth, their levels in the thymus increase, and they contribute to making the body nonresponsive to our own antigens .
Mast cells are a type of white blood cell that generates inflammation when activated. Eosinophils can activate mast cells .
Eosinophils Participate in Tissue Remodeling
Our tissues are under constant renovation, either by a natural process or as a consequence of an injury. For example, eosinophils help regulate the growth of breast gland ducts after birth in mice .
Eosinophil levels in the uterus vary in a cycle, reaching the highest level during ovulation in women. Eosinophils may help prepare the mature uterus for pregnancy. They may also contribute to tissue remodeling before delivery and after childbirth [11, 12].
Eosinophils Help Fight Infections
Eosinophils also help protect against future infections by bacteria, viruses, and parasites by activating acquired immunity (acting as antigen-presenting cells) .
Eosinophils protect us against infections caused by:
- Intestinal worms (helminths) and parasites such as Cystoisospora belli and Dientamoeba fragilis [16, 17]
- Viruses, such as human rhinovirus, parainfluenza virus, and respiratory syncytial virus [18, 19, 20]
- Bacteria, such as Pseudomonas aeruginosa and Staphylococcus [21, 22, 23]
- Fungi, such as Alternaria alternata 
The normal range of eosinophils is 0-0.5 x 10^9/L or less than 500 cells per microliter (mL) of blood (ranging from 0 to 7% of your total white blood cell count) .
However, sometimes, a lab result may be in the reference range, but not actually be in the optimal range. Reference ranges are not the same as an optimal range. This is why eosinophils even in the “normal” range can be unhealthy and indicate that certain processes in the body aren’t optimal.
Health Benefits of High Eosinophil Levels
Eosinophil blood levels are normally elevated when there is an infection. Other than being a sign of a responsive immune system, there are no health benefits from high blood levels of eosinophils.
Harms of High Eosinophil Levels
An above-normal level of eosinophils is called eosinophilia. Depending on how high the blood levels are, it can be :
- Mild (from 500 to 1,500 cells per microliter of blood)
- Moderate (1,500 to 5,000 cells per microliter of blood)
- Severe (more than 5,000 cells per microliter of blood)
Eosinophilia in the blood or tissues can be harmful since eosinophils have granules containing toxic molecules that are meant to kill pathogens. The toxic molecules can also damage the heart, brain, skin, intestines, or lungs when present in large quantities [17, 27].
Causes of High Eosinophil Levels
1) Allergies to Drugs
Some drugs that cause eosinophilia include:
- Antibiotics: Penicillins, cephalosporins, dapsone, and sulfa [29, 30, 31]
- Antiepileptics: Carbamazepine, phenytoin, lamotrigine, and valproic acid [29, 30]
- Antiretrovirals: Nevirapine and efavirenz 
- Others: Allopurinol and ibuprofen [29, 30]
In patients with allergies, eosinophil levels often mildly increase, as in:
- Asthma: Many eosinophils move to the lungs when molecules that cause allergy are present. Their response causes or increases the symptoms of asthma: airway obstruction caused by mucus and dead cells, and altered structure (airway remodeling) .
- Atopic dermatitis: There are elevated numbers of eosinophils in active atopic dermatitis inflammation sites. The molecules secreted by eosinophils are found in the skin of patients and contribute to causing skin lesions and inflammation [33, 34].
- Chronic sinusitis: The disease develops similarly to asthma, but the inflammation caused by eosinophils is more serious .
- Eczema and other skin diseases: High levels of eosinophils are found in skin lesions in urticaria, contact dermatitis, eczema, and prurigo, but not necessarily in the blood .
- Gut diseases: High levels of eosinophils due to allergy can cause inflammation of the stomach, esophagus or intestines (EGID). Some of these diseases include Crohn‘s and ulcerative colitis [37, 38, 39].
- Hay fever: Eosinophils are also in the nasal secretions of patients with allergic rhinitis .
Infections from intestinal worms, parasites, fungi, and viruses often cause an elevation in eosinophil levels. The organisms can be:
- Strongyloides stercoralis 
- Trichinella spp. 
- Ascaris spp. 
- Hookworms, like Ancylostoma duodenale and Necator americanus 
- Toxocara spp. 
- Cystoisospora belli 
- Dientamoeba fragilis 
- Sarcocystis spp. 
- Coccidioides 
- Histoplasma capsulatum 
- Cryptococcus spp. 
- Human T-cell lymphotropic virus type 1 
In several autoimmune diseases, there are high eosinophil blood levels as a reflection of the inflammation present, but eosinophils do not necessarily contribute to the disease .
Some examples are:
- Neuromyelitis Optica, an autoimmune disease where the optic nerve loses its isolating cover 
- Churg-Strauss syndrome, also known as EGPA, a disease that causes damage to the sinus, lungs, and kidneys 
- Sarcoidosis, an autoimmune disease where small lumps of cells (granulomas) form .
- IgG4-related disease, where almost every organ can have inflammatory lesions 
- Celiac disease, a disease where food containing gluten causes an immune response 
High levels of eosinophils can be produced by several kinds of cancerous solid tumors, such as of the stomach, colon, uterus, cervix, breast, bladder, pancreas, mouth, and brain .
In some forms of cancer of blood cells, high levels of eosinophils appear as a consequence of cancer, as in Hodgkin’s lymphoma .
In other cases, eosinophils are the main cancerous cell, such as:
- Acute and chronic eosinophilic leukemia 
- T cell lymphoma 
- Chronic myelomonocytic leukemia 
Diseases Caused by High Eosinophil Levels
In other cases, the presence of high eosinophil levels generates the lesions related to the disease, although the cause of the disease is not always known (idiopathic diseases) .
- Idiopathic hypereosinophilic syndrome 
- Myeloproliferative hypereosinophilic syndrome. There is often heart disease and enlargement of the spleen 
- Lymphocytic hypereosinophilic syndrome. There are often skin lesions and swelling of superficial lymph nodes. In some cases, cancer (lymphoma) might develop [50, 51]
- Episodic angioedema with eosinophilia (Gleich syndrome). Patients have episodes of urticaria (hives), fever, swelling of the skin, weight gain, and eosinophilia every 3 to 4 weeks 
- Familial hypereosinophilic syndrome. It is an inherited condition that might not cause any symptoms. It is mapped to chromosome 5q 31-33, but the specific mutation responsible is not yet identified 
Health Benefits of Low Levels
There are no health benefits from low levels of blood eosinophils since their absence is normal when there are no infections.
Harms of Low Levels
Low levels of blood eosinophils (eosinopenia) are rare. There are no characteristic diseases or symptoms in patients with no eosinophils .
However, in studies with genetically modified mice, the lack of eosinophils diminished the physical barriers (mucus) and protective lymphatic tissue (Peyer’s patches) in the gut, thus altering the composition of the microbiota .
The complete lack of eosinophils affected fat tissue, as well as genetically modified mice in a high-fat diet, had a higher percentage of body fat and lower response to insulin than control mice .
Causes of Low Eosinophil Levels
Glucocorticoids are anti-inflammatory drugs related to steroid hormones. They diminish the production, survival, and function of eosinophils .
When there is an acute infection, several substances are secreted to attract eosinophils to affected tissues. Blood eosinophil levels then rapidly drop. A complete absence of eosinophils is also seen in cases of sepsis [57, 58].
There are several cases of patients with asthma where no blood eosinophils are present .
Patients with a tumor on the thymus (thymoma) can have a complete absence of blood eosinophils .
Ways to Increase and Decrease Eosinophils
Increase Eosinophil Count
- Lower stress levels. Blood eosinophil levels decrease as our body secretes hormones (adrenaline and glucocorticosteroids) when we are under a lot of stress .
- Protect against infections. Having good hygiene habits and protecting yourself against infections can help keep eosinophils at a healthy level since blood levels diminish during acute infections .
- Stop smoking. Smoke lowered lung eosinophil levels in mice, although it did not change blood levels .
Decrease Eosinophil Count
Patients with persistent but benign high eosinophil levels do not need to undergo treatment to decrease their levels. However, periodical check-ups are advised .
Lifestyle Modifications to Decrease Eosinophil Levels
Some simple changes in lifestyle can contribute to lowering eosinophil levels:
- Protect against infections. Having good hygiene habits and protecting yourself against infections can help prevent a rise in eosinophil levels, since some infections, such as intestinal worms, elevated blood levels .
- Stop the use of drugs that elevate eosinophil levels. Allergy to some drugs elevates eosinophil levels. Stopping their use should normalize them .
Natural Ways to Decrease Eosinophil Levels
- Vitamin D. Blood eosinophil levels increase when there is not enough vitamin D. The use of vitamin D decreased eosinophil levels in 44 asthmatic patients in a study (DB-RCT) [61, 62].
- Vitamin A. In mice, lung eosinophils decreased with vitamin A deficiency, while blood eosinophil levels increased with the use of vitamin A. Also, vitamin A byproducts helped increase eosinophil tissue levels in cells [63, 64].
- Ginkgo biloba. The use of ginkgo biloba extracts along with fluticasone reduced eosinophil levels in a trial with 75 asthmatic patients and 15 healthy controls .
- Zinc. A diet with zinc supplements helped decrease eosinophil levels in a model of asthma in rats .
Several extracts from natural products help decrease eosinophil levels in a mouse model of airway allergy:
- Black pepper 
- Galacto-oligosaccharides (GOS) 
- Garlic 
- Ginger 
- Lycopene 
- Onion 
- Rosemary 
- Vitamin E (gamma-tocopherol) 
- Artemisia asiatica 
- Boswellia serrata 
- Pinellia ternata, Citrus reticulata, and their combination (Korean traditional medicine) 
- Black rice (Oryza sativa) 
- Butterbur (Petasites hybridus) 
- Jambolan (Syzygium cumini) 
- Perilla (Perilla frutescens) 
- Red sage (Salvia miltiorrhiza) 
- Curcumin as an addition to an antiparasitic antibiotic helped reduce the number of brain eosinophils in a mouse model of parasitic meningitis .
- Fenugreek (Trigonella foenum-graecum) helped reduce eosinophil levels in a mouse model of skin allergy .
Drugs That Decrease Eosinophil Levels
Please speak to your doctor about these medications before you try to use any of these drugs.
In cases where damage to tissues needs to be controlled, eosinophil levels can be decreased with:
- Anti-IL-5 antibodies decreased the number of eosinophils in clinical trials (DB-RCT with 24 and 32 patients with asthma) [85, 86].
- Glucocorticoids, either inhaled or intranasal [87, 56].
- Myelosuppressives, such as hydroxyurea or vincristine .
- Leukotriene antagonists, such as zileuton or zafirlukast [88, 87].
- Tyrosine kinase inhibitors (Imatinib is used in patients with FIP1L1-PDGFRA+ eosinophilia) .
- IFN-alpha .
- Lidocaine (a local anesthetic) [91, 92].
- Genes/SNPs That Influence Eosinophil Levels.
Genetics Related to Eosinophil Levels
Fusion Genes and High Eosinophil Levels
Mutations that cause the formation of a new gene by the combination of 2 different ones (fusion genes) can result in high blood eosinophil levels, such as:
SNPs and Low Eosinophil Levels
Low eosinophil blood levels are seen in:
- rs1129844 SNP in the eotaxin-1 gene (CCL11) 
- rs2302009 (a SNP in the eotaxin-3 gene (CCL26) found in Korean patients) 
Irregular Eosinophil Levels?
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