Histamine

What is histamine?

Histamine is a signaling chemical your immune system releases to send messages between different cells. Histamine has several functions, but it’s mainly known for its role in causing allergic and anaphylactic symptoms.

Allergies are your body’s reaction to a foreign protein. Usually, these proteins (allergens) are harmless. However, if you have an allergy to a particular protein, your immune system overreacts to its presence in your body.

A cascade of reactions leads to a release of histamine, which causes allergy symptoms. These symptoms are usually confined to one area of your body. If the immune reaction is severe, it causes anaphylaxis, which affects most of your body. Anaphylactic shock is life-threatening.

Your body mainly stores histamine in mast cells in tissues and basophils in blood. Mast cells are a type of white blood cell that’s present in connective tissues throughout your body, especially:

• Under your skin.
• Near blood vessels and lymph vessels.
• In nerves.
• In your lungs and intestines.

Basophils are another type of white blood cell.

What does histamine do?

Histamine regulates countless bodily functions and plays a key role in your body’s inflammatory response. The effect histamine has depends on which histamine receptors it binds to. Researchers have identified four types of histamine receptors.

H1 receptors

You have H1 receptors throughout your body, including in neurons (brain cells), smooth muscle cells of your airways and blood vessels. Activation of the H1 receptors causes the well-known allergy and anaphylaxis symptoms. It causes:

• Itchy skin (pruritus).
• Expanding of blood vessels (vasodilation).
• Low blood pressure (hypotension).
• Increased heart rate (tachycardia).
• Flushing.
• Narrowing of your airways (bronchoconstriction).
• Pain.
• Movement of fluids through blood vessel walls (vascular permeability).

Some of these bodily changes result in sneezing, nasal congestion and runny nose (rhinorrhea).

Outside of allergic reactions, H1 receptors also help regulate:

• Sleep-wake cycles.
• Food intake.
• Body temperature.
• Emotions.
• Memory.
• Learning.

H2 receptors

You have H2 receptors mainly in the cells in your stomach that release acid, smooth muscle cells and heart cells.

Activation of the H2 receptors leads to:

• Stomach acid secretion, which helps with digestion.
• Stimulation of mucous glands in your airways.
• Vascular permeability.
• Hypotension.
• Flushing.
• Headache.
• Tachycardia.
• Bronchoconstriction.

H3 receptors

H3 receptors are mainly involved in blood-brain barrier function. They’re found in neurons in your central nervous system. H3 receptors regulate the release of histamine and neurotransmitters like dopamine, norepinephrine and acetylcholine.

Researchers are currently studying H3 receptor antagonist medications for potential use in the treatment of neurodegenerative diseases.

H4 receptors

H4 receptors are present in your bone marrow and hematopoietic cells (immature cells that can develop into all types of blood cells). They play a role in the formation of certain blood cells.

They also play important roles in inflammatory disorders and autoimmune diseases.

What conditions involve histamine issues?

Histamine plays a central role in several allergic conditions, including:

• Atopic dermatitis (eczema).
• Contact dermatitis, which can happen due to contact with things like poison ivy, fragrances, metals (like nickel) and preservatives.
• Allergic rhinitis (hay fever), which can happen due to pollen, pet dander, dust mites, mold and cockroaches.
• Allergic asthma. The same allergens that trigger allergic rhinitis can trigger allergic asthma.
• Allergic conjunctivitis. This happens when the conjunctiva of your eyes becomes swollen or inflamed due to allergens.

What is histamine intolerance?

Histamine intolerance occurs when you have a high level of histamine in your body. It can happen if your body can’t break down histamine properly. It causes a variety of symptoms, including:

• Headaches or migraines.
• Nasal congestion.
• Fatigue.
• Hives.
• Digestive issues.
• Irregular periods.

How can you clear histamine from your body?

Healthcare providers recommend or prescribe the following medications to help manage histamine levels in your body:

• H1 antihistamines: These are a class of drugs commonly used to treat symptoms of allergies, such as those caused by pollen and pet dander. They do so by blocking H1 receptors. Antihistamines can be prescription or over-the-counter (OTC) medications. They come in several forms, such as tablets, liquids, creams and eye drops.
• H2 antihistamines: H2 antihistamines can help treat several digestive conditions, including peptic ulcer disease, gastroesophageal reflux disease (GERD) and indigestion (dyspepsia). They do so by blocking H2 receptors, which trigger stomach acid release.
• Corticosteroids: Steroids can help with the inflammatory effects of histamines and allergies. Many inhalers that help treat and prevent asthma, for example, have steroid medications in them.
• Epinephrine injections: These injections treat severe allergic reactions (anaphylaxis) or sudden asthma attacks. Epinephrine opens up your airways and increases blood pressure.
• Certain supplements: Studies show that vitamin C, copper and/or vitamin B6 supplements may help lower histamine levels. Talk to your healthcare provider before starting any supplements.

When should I see my healthcare provider about histamine issues?

If you develop signs of seasonal allergies or an allergic reaction, reach out to your provider, especially if your symptoms are affecting your daily functioning. They can perform allergy testing and recommend treatments. Also, see your provider if you have symptoms of histamine intolerance.

A note from Cleveland Clinic

While histamine plays important roles in regulating normal bodily functions like your sleep-wake cycle and cognitive function, it can also wreak havoc when your body overreacts to otherwise harmless allergens. If allergies are affecting your daily life, see a healthcare provider. They can conduct tests to pinpoint your allergies and prescribe medications.