What Are Basophils?

Medically Reviewed by Carmelita Swiner, MD on April 30, 2023
3 min read

Basophils are one of the several kinds of white blood cells you have in your body. These blood cells make up less than 1% of all of your circulating white blood cells and are the least abundant in all mammals. Basophils are a part of your immune system and are created inside of your bone marrow.

There are five kinds of white blood cells in your body, also called leukocytes. These cells, listed from most present to least, are:

  • Neutrophils
  • Lymphocytes (B cells and T cells)
  • Monocytes
  • Eosinophils
  • Basophils

White blood cells are made inside your bone marrow and can be found in your blood and lymph tissues. White blood cells help your body fight off infections and illnesses.

Basophils were first identified in 1879 by researcher Paul Ehrlich. Because basophils aren’t as abundant as other blood cells in humans, scientists at the time thought that they didn’t have much importance. However, around 100 years later, it was noted that there are a few different functions of basophils.

Basophils have a short life span, usually only one or two days. Because of this, research on basophils was often difficult in the past.

These white blood cells are mononuclear cells, so they have one round nucleus. Basophils are also granulocytes, or white blood cells that have granules, or small particles, attached to them. These small particles are filled with enzymes, like histamine, that are released during allergic reactions

Basophils are the only white blood cells circulating around your body that contain histamine. During an allergic reaction, histamine is responsible for many of the typical symptoms of allergies, like a runny nose or sneezing.

The role of basophils was poorly understood for a long time. However, research now shows that basophils function similarly to mast cells. These are white blood cells that are found in the connective tissues throughout your body.

Basophils play a part in "immune surveillance". This means they have the ability to help detect and destroy some early cancer cells. Another important function of basophils is that they release the histamine in their granules during an allergic reaction or asthma attack.

Allergic reactions. Once histamine is released into your bloodstream, it can trigger symptoms in several places. Histamine can act on your:

  • Eyes
  • Throat
  • Lungs
  • Nose
  • Skin
  • Gastrointestinal tract

When your body has an allergic reaction to something, basophils are called upon to react to the inflamed or affected part of the body. To help fight symptoms of an allergic reaction, you can take antihistamine medications.

Protective functions. While these white blood cells are mainly known for causing allergic reactions in people, another function of basophils is to help protect the body. They help protect against:

  • Microbial pathogens
  • Viruses
  • Helminths, or parasitic worms that infect your gastrointestinal tract
  • Venoms from some snakes, scorpions, Gilas, and honeybees

Varying levels of basophils in your blood are associated with different medical conditions. You can learn about your white blood count by having a blood differential test or complete blood count.

A CBC test can check your levels of the five white blood cell types to check for conditions like:

Normally, basophils account for 0.5% to 1% of your white blood cell count. A basophil level that is higher or lower than this amount can point to something irregular.

To perform a differential blood test, your health care provider will ask for a blood sample. A drop of your blood is placed on a glass slide so that it can be inspected under a microscope. Dye is added to the blood so that the different types of white blood cells can be distinguished.

A machine or your health care provider can count the number of each type of white blood cell in the sample, and the results are given a percentage or proportion.

High basophil level. Higher levels of basophils are linked to certain conditions or basophilic disorders. If your percentage is higher than normal, the cause could be one of the following:

  • Chickenpox
  • Allergic reaction
  • Collagen vascular disease
  • Chronic myelogenous leukemia, a kind of bone marrow cancer
  • Bone marrow diseases
  • Hyperthyroidism 

Low basophil level. Low levels of basophils can indicate other basophilic disorders. Some of these include:

  • Cancer
  • Acute infection
  • A serious injury
  • Thyrotoxicosis, a thyroid disorder

Performing a CBC test to determine the amount of basophils in your blood is quite low-risk. Some people may experience discomfort or feel lightheaded while the blood sample is being taken, while others might only feel a quick prick or stinging sensation.