Eosinophils are a type of white blood cell that protect your body from parasites, allergens, foreign bacteria and outside organisms. Eosinophils are larger than most cells and make up less than 5% of all white blood cells in your body.
Eosinophils are a type of white blood cell (leukocytes). There are three types of white blood cells, all with various functions to help your immune system, including granulocytes, lymphocytes and monocytes. Eosinophils are one of three types of granulocytes, along with neutrophils and basophils. Eosinophils prevent foreign organisms from growing inside of host cells (parasites).
Cleveland Clinic is a non-profit academic medical center. Advertising on our site helps support our mission. We do not endorse non-Cleveland Clinic products or services. Policy
When an unfamiliar organism or particle enters your body, your white blood cells divide into special troops to locate and destroy the invader before it causes harm to other cells. Each type of white blood cell undergoes specialized training before leaving your bone marrow and traveling to your tissues where they watch for invaders to enter your body so they can destroy them. Eosinophil cells contain small sand-like granules that release a toxic protein to destroy and consume invading organisms. Eosinophils help your body defend itself from:
Eosinophils are a type of white blood cell that lives in your body’s tissues. The most common place to find eosinophils include:
Eosinophils are microscopic cells that are spherical. The cells are clear in your body but under a microscope, an acidic dye changes the cell’s color to be examined. The dye changes the cell to a purple or pink color.
Eosinophils are larger than other cells and stand out because of their two-lobed nucleus, which looks like two separate raindrops connected by a thread. The nucleus contains the cell’s DNA and floats in a protein that appears sandy in texture (granules).
Eosinophils are a type of white blood cell. White blood cells make up 1% of the cells in your body. There are less than 5% of eosinophils circulating among white blood cells in healthy adults.
Eosinophils form in the soft tissue of your bones (bone marrow). After maturing in your bone marrow, eosinophils travel to fatty tissue in your body, like your stomach.
Conditions that affect eosinophils are rare. There are two types of eosinophil conditions for both low and high cell counts.
Eosinopenia is the result of having a less than normal amount of eosinophils in your body. Types of eosinopenia include:
Often, if you have an occasional low number of eosinophil cells, it doesn’t pose a major threat to your health because other cells in your immune system compensate for the lack of eosinophils. Long-term eosinopenia is dangerous and requires immediate treatment from your healthcare provider.
Eosinophilia occurs when you have more eosinophils in your blood than normal. Your healthcare provider will diagnose a high eosinophil count based on where eosinophils are living:
Symptoms of eosinophil conditions often appear near the location of the disorder. General symptoms of eosinophil conditions include:
There are several factors that affect the number of eosinophils in your blood including:
A high eosinophil count can be the result of a contagious infection, but it is not always the primary cause of eosinophilia. Parasites cause eosinophil cells to increase and parasites spread from human-to-human contact or animal-to-human contact, especially from dogs and cats. Your healthcare provider will test for a parasitic infection to confirm the diagnosis and offer treatment options, which will reduce your eosinophil count to a normal level.
Diagnosing eosinophil conditions starts with a complete blood count test where your healthcare provider will examine a sample of your blood to count the cells in your body, specifically your white blood cells, to make sure those aren’t too high or too low. Other tests to check the health of your eosinophil cells include:
To target the location of the eosinophil condition, your healthcare provider may perform localized tests including:
A normal eosinophil count is between 30 and 350 cells per microliter of blood. A count is higher than normal with results of more than 500 cells per microliter of blood and low if it is less than 30 cells per microliter of blood.
Often, a one-time, low eosinophil count will not be a threat to your overall health, even if your count is zero. Your white blood cells in your immune system will compensate and produce more cells to make up for the lack of eosinophil cells in your body.
Your healthcare provider will classify a high count of eosinophils (eosinophilia) by severity based on the results of an absolute eosinophil count:
Although rare, having a consistently high eosinophil count can be an indication of cancer in your body. A high eosinophil count could relate to several cancers including:
If your healthcare provider suspects cancer, they will perform further tests to diagnose and treat the condition, like a biopsy, additional blood tests or imaging tests.
Treatment for conditions with a high eosinophil count varies depending on the location and severity of the diagnosis. Treatment to reduce a high eosinophil count includes:
Most high eosinophil count conditions are chronic and require long-term treatment and management.
Treatment for conditions with a low eosinophil count includes:
Your body will often detect a low number of eosinophils on its own and other members of your immune system will step up to compensate for the lack of eosinophil cells. Long-term treatment for an underlying health condition may be necessary if your low eosinophil count does not return to normal on its own.
Take steps to keep your eosinophil cells healthy by:
Acidophils are a less common name to identify eosinophils. The name “acidophils” comes from the term “acidophilic” (acid-loving), which specifically relates to how the granules in eosinophil cells change color when you add an acidic stain dye to the sample of cells under a microscope. The stain turns the cells a shade of pink or purple, making them easier to see.
A note from Cleveland Clinic
Eosinophils are an important part of your immune system to defend your body from outside invaders. Your healthcare provider will track the health of your cells through a blood test if they suspect your eosinophils are out of a normal range. Often, a low eosinophil count does not pose a threat to your overall health because other cells will compensate for the missing eosinophils to help your body function.
Last reviewed by a Cleveland Clinic medical professional on 07/05/2022.
Learn more about our editorial process.