What Is Histamine?

Histamine is a chemical that your immune system releases to send messages between cells, according to MedlinePlus.

While histamine is best known for causing an allergic reaction when your body responds to an allergen (a foreign substance), it’s also responsible for many other important functions, per Cleveland Clinic, including:

• Sending messages to the brain
• Telling stomach cells to make stomach acid
• Regulating the sleep-wake cycle
• Helping with cognitive function
• Triggering a response to an injury or infection

Histamine is present throughout the body, but it is mainly stored in mast cells and basophils, according to an article published in StatPearls. Mast cells are white blood cells that are mostly present in loose connective tissue, such as in the lungs, under the skin, in the intestines, near blood vessels, in nerves, and close to lymph vessels. Basophils are another type of white blood cell that form in the bone marrow. When they mature, basophils travel through the bloodstream to damaged tissues in order to heal them after injury.

Normally, histamine works to protect you from foreign pathogens, notes MedlinePlus. But in some people, when the body is exposed to an allergen such as dust, pollen, or dander, the immune system mistakenly thinks the substance is harmful and overreacts. Nemours KidsHealth explains that, in an effort to protect your body, your immune system releases histamine and other chemicals into the bloodstream.

When histamine is released, it acts on the eyes, throat, lungs, nose, skin, or gastrointestinal tract, according to Nemours. The chemical can cause allergy symptoms, such as a runny nose, sneezing, itching, swelling, and watery eyes. Cleveland Clinic notes that if the immune reaction is severe, it can lead to anaphylaxis, which can be life-threatening.

Histamine is also involved in food allergies, according to MedlinePlus. If you eat or drink something you’re allergic to, histamine can trigger symptoms, such as vomiting, diarrhea, or difficulty breathing.

According to Cleveland Clinic, the effect of histamine depends on which receptor it binds to. There are four types of histamine receptors in our bodies:

• H1 receptors are present throughout the body, including in brain cells, smooth muscle cells of airways, and blood vessels. When these receptors activate, they can cause allergy symptoms, such as a runny nose, sneezing, and congestion. Additionally, they can trigger anaphylaxis symptoms, such as itchy skin, low blood pressure, expanding blood vessels, constricted airways, flushing, and increased heart rate. H1 receptors also regulate sleep-wake cycles, body temperature, emotions, memory, and food intake.
• H2 receptors are primarily found in the stomach, smooth muscle cells, and heart cells. When activated, they can cause stomach acid secretion, low blood pressure, flushing, headache, increased heart rate, tightening of airways, and stimulation of mucous glands in airways.
• H3 receptors are found in nerve cells. They regulate the release of histamine and other chemicals, such as dopamine, norepinephrine, and acetylcholine.
• H4 receptors are present in the bone marrow and hematopoietic cells (immature cells that can develop into different types of blood cells). Researchers believe H4 receptors are a factor in inflammatory conditions and autoimmune diseases.

According to StatPearls, some allergic conditions that are related to the release of histamine include:

• Atopic dermatitis (eczema), an inflammatory skin condition that causes dry skin, rashes, scaly patches, and itchiness
• Contact dermatitis, a skin reaction that occurs when someone comes in contact with an irritant, such as fragrances, cosmetics, metals, or plants
• Allergic conjunctivitis, in which eyes become swollen, itchy, red, or inflamed because of a reaction to an allergen
• Allergic rhinitis (hay fever), an allergic reaction that can cause sneezing, a runny nose, congestion, itchy eyes, and a sore throat.
• Allergic asthma, a condition that occurs when allergens trigger asthma symptoms.

Histamine intolerance means you have too much histamine in your body, per the Cleveland Clinic. According to a study published in April 2021 in Nutrients, histamine intolerance primarily happens when a person has low levels of diamine oxidase (DAO), the enzyme that helps break down digested histamine.

In an analysis of patients’ records published in July 2019 in Intestinal Research, authors point out that symptoms of histamine intolerance vary greatly and often mimic those of other conditions. Some common signs may include:

• Bloating
• Digestive issues
• Headaches
• Flushing
• Congestion
• Watery eyes or itchy nose
• Heart palpitations
• Dizziness
• Low blood pressure
• Hives
• Tightening of airways in the lungs

A study published in March 2022 in Biomolecules found that the following factors could contribute to histamine intolerance:

• A gene mutation
• Certain medications, such as blood pressure meds, phlegm reducers, antiarrhythmics, antiemetics, antibiotics, or antidepressants
• Other medical diseases, such as allergic conditions or inflammatory bowel disease (IBD)
• A diet rich in certain foods that trigger histamine release
• Bacterial overgrowth

If doctors suspect a histamine intolerance, they may recommend following a diet low in histamine-rich foods, according to a study published in 2020 in Biomolecules. The authors of this paper also note that supplements to boost DAO may be helpful for some individuals, but more research is needed to confirm these findings.

Some common histamine-rich food include:

• Seafood
• Sauerkraut
• Smoked meat
• Bacon
• Cheese
• Pickles
• Spinach
• Eggplant
• Tomatoes
• Alcohol

Though histamine intolerance has been studied extensively in recent years, there is some debate in the medical community about how to approach the condition. The 2020 Biomolecules study shows there are still many unanswered questions when it comes to effectively diagnosing and treating high levels of histamine in the body.

According to the Cleveland Clinic, some medicines that can protect against histamine levels in the body include:

• H1 antihistamines These medicines work by blocking H1 receptors and are commonly used to treat symptoms of allergies.
• H2 antihistamines They block H2 receptors, which trigger stomach acid release. H2 antihistamines are typically taken to help digestive problems, such as peptic ulcer, indigestion, or gastroesophageal reflux disease (GERD).
• Epinephrine It’s used for severe allergic reactions or asthma attacks to open up airways.
• Corticosteroids Steroids can lessen the inflammatory effects of histamine.
• Supplements Some supplements, like vitamin C, copper, and vitamin B6 may possibly lower histamine levels.