Mast cells are your body’s alarm system. They look out for harmful invaders, like parasites. When they recognize something harmful, they send out signals that open your blood vessels, fill your tissues with fluid and contract muscles in your GI tract and airways. Sometimes, they activate when they shouldn’t, causing allergic reactions.
Mast cells are a part of your immune system. They’re made in your bone marrow, then move through your bloodstream into your tissues. The mature mast cells live in tissues throughout your body to help protect you from hazards around you. They can help fight infections and regulate your organs.
When your mast cells are overprotective, you may react to harmless things in your environment. This happens in people with seasonal allergies or allergic asthma. Mast cell activation can sometimes cause anaphylaxis, a serious allergic reaction.
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Mast cells act like an alert system. They protect your body from foreign invaders (pathogens like viruses, bacteria and parasites) and toxins (for instance, venom from snake bites or bee stings). They also fight off particles they think are harmful, even when they’re not. This causes allergic reactions.
Unlike many other types of white blood cells, they don’t destroy pathogens themselves. Instead, they sit in your tissues and wait for a message that something harmful is in your body.
Mast cells stand guard, ready to activate a quick response against invaders. They use surface proteins (receptors) that act like antennas to receive incoming immune signals. Other immune cells communicate which invaders to look out for, and sound an alarm if they find an intruder.
When your B cells (cells of your immune system) identify an invader, they become specialized to create lots of immunoglobulins (antibodies) to fight that particular invader. Immunoglobulin E (IgE) is the specific antibody made to alert the mast cells. IgEs quickly find and latch onto the IgE receptors on mast cells. The next time the same pathogen or allergen enters your body, the IgEs will catch it, like a fishing lure.
This will “switch on” (activate) the mast cells, which is kind of like pulling the fire alarm. But instead of fire doors closing, sprinklers spraying water and the fire department being alerted, the mast cells release histamine from their storage granules (degranulate). The shower of histamine causes a series of events that:
This can make your skin flushed, swollen or itchy. You might get a runny nose or sneeze and cough. You might even get diarrhea or vomit. In extreme cases, it can cause swelling of your airways and a life-threatening drop in blood pressure (severe anaphylaxis).
Mast cells also play a role in regulating your tissues and organs and keeping them in balance (homeostasis), including:
Unlike most of your white blood cells, very few mast cells are found in your bloodstream. You’re most likely to be exposed to something harmful by inhaling it, eating it or getting it in a break in your skin from injury. That’s why mast cells are mostly found in the tissues of your:
They also surround your blood vessels and nerves.
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Mast cells contain a nucleus (the “brain” of the cell) surrounded by hundreds of granules (storage pouches). The granules contain chemical messengers (mediators) that send signals to your body in response to something that might harm you. These include:
Mast cells have many receptors on their surface. These specially shaped proteins fit with other signaling proteins like a lock and key to activate the mast cells.
The most well-known mast cell receptor is the IgE receptor. Mast cells also have receptors for other antibodies (like immunoglobulin G or IgG) and ones that directly detect pathogens (toll-like receptors).
Some common mast cell disorders include:
Some rare mast cell disorders include:
The histamine released in mast cell disorders can lead to symptoms like:
If your provider thinks you have a mast cell disorder, they might check for signs of mast cell activation in your:
Your provider might do an allergy skin test or blood tests to identify triggers or look for signs of mast cell activation. A lab may do genetic testing to check for inherited conditions that might cause your symptoms.
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Treatments for mast cell disorders depend on your symptoms and what’s causing them. Treatments might include:
Since most people have never heard of mast cells until they’re making you sick, you might think mast cells are bad. But they actually help defend your body against harmful invaders and regulate your organs. So, most of the time, they’re good.
A note from Cleveland Clinic
Sirens are going off. Security’s on the scene. Your mast cells have sounded the alarm, and your immune system is rushing in to save the day. They’re a vital part of our body’s defense system, but you usually only notice mast cells when they’re a little too over-enthusiastic about their job. But they strengthen our defenses and help regulate our blood vessels and organs. So next time you sniffle, sneeze or itch, thank your mast cells for their vigilance.
Last reviewed on 05/16/2024.
Learn more about the Health Library and our editorial process.
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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