Causes

Eosinophils play two roles in your immune system:

• Destroying foreign substances. Eosinophils can consume foreign substances. For example, they fight substances related to parasitic infection that have been flagged for destruction by your immune system.
• Regulating inflammation. Eosinophils help promote inflammation, which plays a beneficial role in isolating and controlling a disease site. But sometimes inflammation may be greater than is necessary, which can lead to troublesome symptoms or even tissue damage. For example, eosinophils play a key role in the symptoms of asthma and allergies, such as hay fever. Other immune system disorders also can contribute to ongoing (chronic) inflammation.

Eosinophilia occurs when a large number of eosinophils are recruited to a specific site in your body or when the bone marrow produces too many eosinophils. This can be caused by a variety of factors, including:

• Parasitic and fungal diseases
• Allergic reactions
• Adrenal conditions
• Skin disorders
• Toxins
• Autoimmune disorders
• Endocrine disorders
• Tumors

Specific diseases and conditions that can result in blood or tissue eosinophilia include:

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

Parasitic diseases and allergic reactions to medication are among the more common causes of eosinophilia. Hypereosinophila that causes organ damage is called hypereosinophilic syndrome. This syndrome tends to have an unknown cause or results from certain types of cancer, such as bone marrow or lymph node cancer.