The Role of Basophils in Your Body

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A basophil is a type of white blood cell that is a part of your immune system. They make up only around 1% or less of all white blood cells but are among the largest. The cells not only provide frontline defense against infection but are also involved in processes like inflammation and allergy.

This article details the structure and function of basophils as well as the diseases and conditions associated with high or low basophils.


Verywell / Laura Porter


Basophils are a type of white blood cell, also known as a leukocyte. White blood cells play in role in the body's immune defense and protect the body against infectious disease and foreign invaders.

Like all blood cells, white blood cells arise from stem cells in the bone marrow. In a process called hematopoiesis, the stem cells develop into different types of blood cells, including white blood cells, red blood cells, and platelets.

Basophils belong to a category of white blood cells that are called granulocytes because they contain tiny granules. The granules in basophils are made up of different chemicals, including histamine and heparin. When needed, basophils will break open (degranulate) to release these chemicals as part of the body's immune defense.


Basophils are part of the innate immune system. This is the immunity you are born with as opposed to immunity you later develop after infection or vaccination.

As part of the innate immune system, basophils do not make you immune to an infection you have had in the past. They are simply among the frontline cells that attack any foreign agent that enters the body.

Basophils are most effective in protecting against bacteria and parasites, including parasites like ticks and worms.

Action of Basophils

Basophils help trigger inflammatory reactions. Inflammation is the body's natural response to anything that might cause it harm. It is the body's way of signaling the immune system to heal and repair damaged tissues as well as defend itself against foreign agents.

The granules inside the basophils contain histamine and heparin, among other things. Each has a different role:

  • Histamine is a vasodilator, meaning that it causes blood vessels to widen. This brings more immune cells to the site of an injury or infection.
  • Heparin is an anticoagulant (blood thinner). It is produced by the body to prevent blood clots from forming at the site of an injury or infection.

Basophils also indirectly attack foreign agents by binding to a type of white blood cell called B-cell lymphocytes. The binding causes B-cells to release antibodies called immunoglobulin E (IgE) into the bloodstream. IgE has strong action against parasites and venoms.


Basophils are part of the body's frontline immune response. They are involved in triggering inflammation in response to injury or infection and play a role in releasing antibodies to fight parasites like ticks and worms.

Abnormal Counts

The composition of white blood cells is measured with a test called a white blood cell (WBC) count, of which basophils account for between 0.5% to 1%. The actual number of basophils is measured with a test called the absolute basophils count (ABC) described in cubic millimeters (mm3).

A normal ABC is between 15 and 50 mm3. When the count is outside of this range, it is considered abnormal. These abnormalities are described as either basophilia (high basophils) or basopenia (low basophils):


High or low basophils can occur with certain diseases or in response to certain treatments. An abnormally high basophil count is known as basophilia, while abnormally low basophils are called basopenia.

Basophils' Role in Allergies

An allergy is an abnormal response by the immune system to a substance or event that is otherwise harmless. The histamine released by basophils is one of the main causes of allergy symptoms. When the body is exposed to an allergen (allergy-causing substance), basophils and related cells called mast cells will break open.

The release of histamine causes blood vessels to widen, which causes fluid to leak into surrounding tissues. This can lead to redness and swelling of the skin in the form of rash, hives, or angioedema as well as nasal symptoms and breathing problems as those tissues swell and become inflamed.

Histamine is also involved in itching. It does so by attaching to proteins called H1 receptors in the skin, triggering abnormal sensations in surrounding nerve fibers.


Basophils play a role in allergies. When called by the immune system, basophils will break open and release histamine into the bloodstream. Histamine is one of the main causes of allergy symptoms.


Basophils are a type of white blood cell called a granulocyte. As part of the innate immune system, basophils are one of the frontline defenders against diseases, including parasites.

High basophils (basophilia) may be caused by infections, autoimmune diseases, and cancer, while low basophils (basopenia) may be caused by acute infection, severe allergies, medications, and cancer treatments. Basophils also play a role in allergies by releasing an allergy-causing chemical called histamine into the bloodstream.

Frequently Asked Questions

  • What is a basophil?

    A basophil is a type of white blood cell. Although basophils are the least common white blood cell, they are the largest in terms of size. Basophils, along with neutrophils and mast cells, are classified as granulocytes because they contain granular chemicals that help fight infection.

  • What is the function of basophils?

    Basophils store chemicals that help coordinate the immune response. This includes histamine that helps trigger inflammation and heparin that prevents blood clots. When called upon, basophils will degranulate (break open) to release these chemicals.

  • What role do basophils play in allergies?

    Histamine, a chemical released by basophils as part of normal inflammation, can sometimes be released when the immune system overreacts to an otherwise harmless substance (known as an allergen). When this occurs, the rapid swelling of blood vessels and tissues can trigger the respiratory, skin, and gastrointestinal symptoms of allergy.

  • What is a normal basophil count?

    Basophils account for between 0.5% and 1% of your total white blood cells. A normal absolute basophil count, calculated by multiplying the percentage of basophils by the total white blood cell count, is between 0 and 300 cells per microliter (μL).

  • What does it mean if my basophils are high?

    Basophilia is an abnormally high basophil count. On its own, basophilia is not diagnostic of any medical condition but can help inform the diagnosis. Possible causes include:

  • What does it mean if my basophils are low?

    Basopenia is an abnormally low basophil count. Causes include:

    • Ovulation
    • Urticaria (hives)
    • Angioedema
    • Hyperthyroidism
    • Hypersensitive drug reactions, such as Stevens-Johnson syndrome
    • Anaphylaxis
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