You have probably taken an antihistamine at some point during your life when your allergies started to flare up, but have you ever stopped to ask yourself, “What exactly is a histamine?”

A histamine is a neurotransmitter that helps your body respond to foreign invaders such as germs and bacteria. If histamine levels become too high, you can experience symptoms often associated with allergies. Or, if they approach dangerously low levels, you can go into anaphylactic shock.

How Is Histamine Produced and Stored?

Histamine is produced when a carboxyl group is removed from the amino acid called histidine. The reaction is catalyzed by an enzyme.

When histamine is formed, it is either used immediately or stored for later use in mast cells or white blood cells. Histamine is often stored in areas that are prone to infection or injury, such as your feet, hands and skin, so that it can be quickly released if necessary.

What Do Histamines Do?

When a foreign body enters the body or when the body sustains an injury, histamine is released and works to protect the body. The body will release immunoglobulin E, an antibody. Once the histamine is released, it helps the body in a variety of unique ways depending on which receptors it interacts with.

The Four Histamine Receptors

Histamine can come into contact with four different types of receptors, and depending on which it interacts with, the body will produce a different physiological response.

  1. H1 Receptor: Making the body alert and awake, the H1 receptor is especially important during the fight-or-flight response. H1 receptors can also cause symptoms typically associated with allergies, such as nasal congestion, runny nose, irritated skin, swelling in the joints, hives and broncho-constriction.
  2. h4 Receptor: The h4 receptors, found in the epithelial cells lining the stomach, work to stimulate the generation of gastric acid and can also cause smooth muscles to relax.
  3. H3 Receptor: Interaction with the H3 receptors, which are located in the brain, will cause the histamine production to halt immediately once enough histamine has been released into the blood stream. H3 receptors also decrease the release of hormones such as serotonin, acetylcholine and norepinephrine, actions thought to be related to proper sleep.
  4. H4 Receptor: A reaction with the H4 receptor allows for regulation of white blood cells located in bone marrow, cells which are very important for immune system response.

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