Some people have eosinophils, a type of white blood cell, in tissues or in their blood. Eosinophils ordinarily play a role in immunity. This is why eosinophil levels may be elevated when you have an infection or inflammation.

However, if an individual has eosinophilia, he or she may experience a buildup of eosinophils in the intestines, skin, or lungs. This condition is often the result of an allergic reaction. For example, tissue eosinophilia can result from inhaling or ingesting the proteins found in dust mites, cockroaches, rats, and cats.

Now, what is eosinophilia? Read on to find out.

Eosinophilia is caused due to excessive production of eosinophils. These are white blood cells that play a role in a body's immunity. The normal range of eosinophils count in the bloodstream is between 0 and 450 cells per cubic millimetre of blood. When an allergic reaction occurs, eosinophils move into the affected area and release various toxins into the bloodstream. They attack substances such as foods and airborne allergens that the body mistakes for harmful invaders. When a person has excessive eosinophils in the body, it can lead to chronic inflammation and tissue damage.

When a patient's eosinophil levels are high, the patient may experience a wide array of symptoms depending on which organ is affected. For example, a rash may result when an individual's skin is affected. Wheezing and shortness of breath are common symptoms of lung disease, while shortness of breath and fatigue may be symptomatic of heart failure. Throat and stomach pain can indicate that the oesophagus or stomach is affected.

The causes can be related to some specific diseases and conditions that can result in blood or tissue eosinophilia, that are as follows –

• Acute myelogenous leukaemia (AML)
• Allergies
• Ascariasis, a roundworm infection
• Asthma
• Atopic dermatitis (eczema)
• Cancer
• Churg-Strauss syndrome
• Crohn's disease
• Drug allergy
• Eosinophilic esophagitis
• Eosinophilic leukaemia
• Hay fever or allergic rhinitis
• Hodgkin's lymphoma
• Hypereosinophilic syndrome
• Idiopathic hypereosinophilic syndrome (HES) occurs with extremely high eosinophil counts.
• Lymphatic filariasis, a parasitic infection
• Ovarian cancer
• Parasitic infection
• Primary immunodeficiency
• Trichinosis, a roundworm infection
• Ulcerative colitis, a type of inflammatory bowel disease

Diseases that involve various organs and systems are as follows –

• Skin
• Lungs
• Gastrointestinal system
• Neurological system
• Joints
• Connective tissue and muscles
• Heart

Eosinophilic disorders are often named where abnormal white blood cells, or eosinophils, are collected in the body. These include:

• Eosinophilic cystitis - A disorder involving the bladder.
• Eosinophilic fasciitis - A disease of the connective tissue throughout the body, its symptoms include many varieties of aches and pains.
• Eosinophilic pneumonia - A disorder involving the lungs.
• Eosinophilic colitis - A disease involving the large intestine.
• Eosinophilic esophagitis - A disorder involving the oesophagus.
• Eosinophilic gastritis - A disease involving the stomach.
• Eosinophilic gastroenteritis - A disorder involving both the small intestine and stomach.

When a doctor orders blood tests, high numbers of eosinophils may be noted. Further, they might order other tests to pinpoint the cause of these high levels. They are as follows –

• Liver function tests
• Chest X-rays
• Urine tests
• Further blood tests
• Tissue and bone marrow biopsies
• Stool sample testing

Individuals with eosinophil-mediated conditions are treated using a variety of medications, depending upon the cause of the disorder. For example, individuals with asthma are treated with inhaled corticosteroids and bronchodilators, anti-inflammatory medications for eosinophilic gastrointestinal disorders, and antihistamines for eosinophilic esophagitis. The FDA has approved medications that target eosinophils, specifically in asthma. In contrast, therapies for other related eosinophil-mediated conditions have been utilised off label to treat individuals but are still under investigation.

Many diseases involve an increase in the number of eosinophils, a type of white blood cell. These disorders range from allergic reactions to hormone imbalances. When one's number of these cells is only slightly elevated, symptoms are often not apparent.

When a person is highly allergic to something, the body sends ever-increasing amounts of eosinophils to attack the allergen. These eosinophils inflame nearby tissues, causing pain and damage to surrounding organs such as the heart, lungs, skin, and nervous system.