Eosinophils play two roles in your immune system:

• Destroy foreign substances. Eosinophils consume matter flagged by your immune system as harmful. For example, they fight matter from parasites.
• Control infection. Eosinophils swarm an inflamed site when needed. This is important to fight disease. But too much can cause more discomfort or even tissue damage. For example, these cells play a key role in the symptoms of asthma and allergies, such as hay fever. Other immune system issues can lead to chronic inflammation as well.

Eosinophilia happens when eosinophils swarm a site in the body. Or when the bone marrow makes too many. This can happen due to many reasons including:

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

Certain diseases and conditions that can cause 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 — which causes tissues in the digestive tract to become inflamed.
• Drug allergy
• Eosinophilic esophagitis
• Eosinophilic leukemia
• Hay fever (also known as allergic rhinitis)
• Hodgkin lymphoma (Hodgkin disease)
• Hypereosinophilic syndrome
• Idiopathic hypereosinophilic syndrome (HES), an extremely high eosinophil count of unknown origin
• Lymphatic filariasis (a parasitic infection)
• Ovarian cancer — cancer that starts in the ovaries.
• Parasitic infection
• Primary immunodeficiency
• Trichinosis (a roundworm infection)
• Ulcerative colitis — a disease that causes ulcers and swelling called inflammation in the lining of the large intestine.

Parasites and allergies to medicines are common causes of eosinophilia. Hypereosinophilia can cause organ damage. This is called hypereosinophilic syndrome. The cause for this syndrome is often unknown. But it can result from some types of cancer such as bone marrow or lymph node cancer.

Often, your care team will find eosinophilia while running blood tests to diagnose symptoms you already have. So, it may not be unexpected. But sometimes it can be found by chance.

Talk to your care team about your results. Proof of eosinophilia along with other test results may pinpoint the cause of your illness. Your doctor may suggest other tests to check your condition.

It's important to know what other health conditions you may have. Eosinophilia will likely resolve with the right diagnosis and treatment.

If you have hypereosinophilic syndrome, your care team may prescribe medicines such as corticosteroids. Because this condition can cause major concerns over time, your care team will check up with you regularly.