What Are Basophils?

Written by Alicia Racelis, PhD, WebMD Editorial Contributor
Medically Reviewed by Poonam Sachdev on April 27, 2025
8 min read

Basophils are the rarest type of white blood cell (WBC). Sometimes called granulocytes, the cells hold tiny granules full of histamine. Basophils can also trigger your allergic reaction. They can protect you from parasites and help heal cuts, too.

Basophils normally stay in your bloodstream. Once active, they quickly release the granules. These histamine particles are a key part of allergy symptoms.

If basophils enter your gut, airways, or skin, it may mean you have allergies or another medical problem. In fact, doctors use basophils to diagnose some blood cancers (such as leukemia). Learn about the properties, function, and levels of basophils.

Less than 1% of your white blood cells are basophils. Key basophil properties help diagnose some medical conditions. Your doctor can test your basophils. They'll look at the number of basophils in your blood sample. 

Here are some other properties to identify basophils:

Basophil size. Basophils are roughly half the size of a cloud droplet. They're about 5-10 micrometers (μm). 

Basophil color. You can see your basophils under a microscope. Special dyes (Wright-Giemsa) stain the granules dark purple. The granules contain histamine, heparin, and peroxide.

Cell center (nucleus). The center (nucleus) of the basophil looks like the letter S. The cell's center has two lobes. 

Location and life span. After about seven days, basophils grow up from stem cells. Basophils mature in your bone marrow. Your bone marrow is the spongy center of your bones. Basophils enter your bloodstream to live about 60 hours, but they usually don't get into your tissues.

Cell surface markers. Key cell surface proteins (markers) can identify basophils. These markers can help diagnose certain blood cancers (leukemia). Here are a few common cell surface markers on basophils: 

  • CD-123, also called interleukin-3 (IL-3) receptor alpha chain, is a common marker for acute myeloid leukemia (AML).
  • CD-193, also called chemokine receptor 3 (CCR3), plays a role in allergy.
  • CD-203a helps keep cell growth in check.

Basophils mainly function (work) to release histamine granules. The granulocytes have other key functions:

  • Protect you from allergens
  • Fight off parasites
  • Repair cuts
  • Help get rid of blood clots (release heparin granules to dissolve clots)

Basophils usually supply histamine to an area. In fact, basophils are the only white blood cells with histamine. And histamine helps your body flush out and clean an area by: 

  • Raising blood flow
  • Slightly opening blood vessels to leak out plasma (clear fluid in your blood)
  • Washing the area with more blood flow
  • Causing swelling and inflammation to heal the site

Basophils release other chemicals such as cytokines. These signals bring other immune cells to the area. This can prompt allergic reactions, too. You can get allergic reactions in your skin, airway, or gut. And rarely, basophils show up in cancer.

Allergic reactions 

Basophils are activated during an allergic reaction. The allergen (invader) can trigger histamine release. The histamine raises blood flow to the tissues.

Histamine. It also causes swelling and inflammation. Histamine helps your body get rid of the allergen. Sometimes, the area can be itchy, too. 

During an allergic event, may get a runny nose or sneeze. It's the histamine causing your allergy symptoms. You can also get histamine symptoms in your:

  • Eyes
  • Throat
  • Lungs
  • Nose
  • Skin
  • Gastrointestinal tract (gut)

Basophils can make histamine during an asthma attack, too. To help fight histamine symptoms, ask your doctor about an antihistamine. 

Cytokines. Cytokines such as IL-4 and IL-13 also support your allergic response. These signals bring other immune cells to fight off infection. And IL-4 helps your B cells make antibodies. B cells help fight infection as part of your immune system.

Immunoglobulin E (IgE). It's a type of antibody made by B cells. IgE can help get rid of allergens. A small amount of IgE coats your stomach and airways, too.

But if you have allergies, your immune system can make too much IgE. IgE can bind to allergens, which are chemical invaders. Basophils attack the IgE-allergen complex to release histamine. 

Histamine causes inflammation in the area. It also promotes blood flow and healing, too. 

Basophils and IgE likely work to rid your body of certain venoms. Histamine release can cause muscle spasm, inflammation, and sweating. Basophils may help your body process venoms from:

  • Snake
  • Scorpion
  • Honeybee

Protective functions 

Basophils can also play a part in "immune surveillance." This means basophils can:

  • Detect and destroy invaders like parasites
  • Find and kill cancer cells
  • Repair and form scar tissue (heal cuts)
  • Release heparin to prevent blood clots

IgE, cytokines, and basophils can work together to kill parasites. Basophils make IL-4 and IL-13 to fight infection. IL-4 may help protect you from parasites, too. Basophils can attack parasitic worms and ticks infecting you, such as:

  • Toxocara, a roundworm found in cats and dogs
  • Ascaris, a roundworm found in pigs
  • Strongyloides, a roundworm found in dogs
  • Schistosoma, a blood trematode (fluke) found in snails
  • Borrelia burgdorferi, the tick causing Lyme disease

On average, you'll have less than 1% of basophils in your blood. The other 99% of your white blood cells are made up of neutrophils, eosinophils, lymphocytes, and monocytes. 

Basophils, eosinophils, and neutrophils all contain granules, but basophils have the most. And the basophils mainly have histamine particles. 

Test for basophils

Your levels of basophils can change depending on your health. Less or more can mean infection or another medical condition. Your doctor may order a complete blood count (CBC) with a differential. This blood test counts the number of white blood cells in your blood sample and your basophils. 

Most often, a hematology (study of blood) machine counts your basophils. Basophils have special electrical and light properties. Some machines use light and high electromagnetic radiofrequency (RF) to detect basophils. RF is the same energy used for your cell phone or Wi-Fi.

Other hematolgy machines use cytochemistry (cell chemistry). This method adds a special dye to your blood sample. Then, the machine uses light to detect the color of your basophils.

Number of basophils

‌The hematology machine can quickly count all your basophils. The machine can count tens to thousands of cells at a time. If your level is too high or low, the machine will flag your blood sample. Then, sometimes the laboratory counts your basophils using a microscope.

Here's a few common ways to measure basophils:

Absolute basophils. It's the total number of basophils in your blood sample. Absolute count multiplies the percent basophils by the total number of white blood cells in your blood sample. The absolute basophil number can depend on your age and medical condition, too.

For adults, the absolute basophil number usually ranges from 0.01 x 109 to 0.08 x 109 per Liter (L). But check the range with your laboratory report. Each laboratory can have a slight difference in the range. That's because they can use various counting methods.

Normal basophil count.Normally, basophils make up 0%-2% of your white blood cell count. Check your laboratory report. This percentage can change slightly. It can depend on the way your laboratory counts.

High basophil level. A higher number of basophils is called basophilia. It usually means more than 0.1 x 109 per L. Basophilia can also be more than 2% of all white blood cells. 

But check your laboratory report. The lab range can be slightly different. A high basophil level is above the range listed. With cancer, basophils can be more than 1 x 109 per L. 

Low basophil level. A low level of basophils is called basopenia. For an absolute count, it's lower than 0.01 x 109 per L. Check your laboratory report for the lowest range. This number can vary depending on the laboratory.

Basophilia means you have a higher number of basophils. Many common conditions can raise your levels. More basophils can mean you have:

  • Allergic reaction to drugs, food, or inhaled irritants
  • An infection, such as chickenpox, influenza, or tuberculosis
  • Hypothyroidism (not enough thyroid hormone)
  • An inflammatory condition, such as atopic dermatitis
  • A blood disorder, such as polycythemia vera
  • A blood cancer, such as chronic myeloid leukemia (CML) or others

Allergic conditions 

Basophils are higher during allergic reactions. Your body signals to other immune cells in the area. This can lead to allergic reactions to an invading substance.

Here are some common allergic conditions with basophilia:

Atopic dermatitis.Allergies can bring basophils into your skin. Often, atopic dermatitis raises your basophils. They release histamine and cytokines in your skin. These signals can cause intense itch, inflammation, and swelling. Higher basophils can contribute to flares and rash.

And the cytokines (IL-4 and IL-13) can break down your skin's barrier. Your skin can lose water, get dry, and itch.

Asthma. If basophils enter your airways, you may get asthma. You can also get chronic sinus problems (rhinosinusitis). IL-4, IL-13, and other immune cells can inflame your airways, too.

Sometimes, the basophils also cause nasal polyps. It's called a triad — chronic rhinosinusitis, nasal polyps, and asthma.

Cancer and basophils

Some types of myeloid cancers have higher basophils. Myeloid cancers affect your bone marrow and blood. These leukemias can include:

  • Chronic myeloid leukemia (CML) 
  • Acute monocytic leukemia (AML)
  • Acute megakaryoblastic leukemia
  • Acute basophilic leukemia

In the later phase of CML, basophils make up 20% or more of your white blood cells. More basophils in your bone marrow can stop other blood cells from forming. Instead, cancer cells are made. 

A very rare leukemia, acute basophilic leukemia, has basophils with coarse granules. These histamine particles can cause skin problems, larger organs, bone lesions, and other symptoms.

Basopenia means lower amounts of basophils. This can impact your body's ability to repair tissues. You may have lower basophils if you have:

  • Infections
  • Systemic lupus erythematosus (in which basophils get in your lymph nodes)
  • Hyperthyroidism (make too much thyroid hormone)
  • Chronic spontaneous urticaria (in which basophils cause itchy hives on your skin)
  • Scar tissue (fibrosis) in your heart, lung, or kidney
  • Hypersensitive allergic reactions (anaphylaxis)

Repair and scar tissue

Basophils usually release IL-4 and IL-13. These cytokine signals help repair your tissues. But with basopenia, scars (fibrosis) can form. You can have lower basophils if you have:

  • Rare blood cancer forming scar tissue in your bone marrow (myelofibrosis)
  • Fibrosis of the kidneys
  • Heart fibrosis (after heart attack)
  • Chronic obstructive pulmonary dysfunction (COPD)

Hypersensitivity

Although your allergic response is usually harmless, it can react too strongly. Studies suggest basophils may be involved. This hypersensitive reaction can be life-threatening (anaphylaxis).

Basophils are hard to test. The exact role basophils play in hypersensitivity is still unclear. The histamine in anaphylaxis likely comes from mast cells and basophils, though. Mast cells are also granulocytes, but they stay in your tissues.

When to see a doctor?

Get medical help right away for anaphylaxis symptoms. Get help if you have:

  • Lip, throat, or face swelling
  • Trouble breathing
  • Trouble swallowing
  • Hives or red rash
  • Cramps, diarrhea, or vomiting
  • Wheezing or chest tightness
  • Belly pain
  • Feeling of doom

What does a 1% basophil count mean?

A 1% basophil count is normal. Most people have 0.5%-1% of basophils.

Is 0.01 basophil normal?

Check your laboratory report to be sure, but 0.01 is likely normal. A 0.01 basophil likely means an absolute count. It depends on the laboratory, but the absolute basophil count ranges from 0.01 x 109 to 0.08 x 109 per Liter (L). 

What medical conditions can cause low basophils?

Many medical conditions can cause low basophils (basopenia). The most common reason for basopenia is infection. Systemic lupus erythematosus, hyperthyroidism, and anaphylaxis can also lower your basophil count.