What Are Histamines?

Medically Reviewed by Nayana Ambardekar, MD on August 14, 2022
3 min read

You've probably heard of antihistamines. They're medicines that tame allergy symptoms. But what are histamines?

They're chemicals your immune system makes. Histamines act like bouncers at a club. They help your body get rid of something that's bothering you -- in this case, an allergy trigger, or "allergen."

Histamines start the process that hustles those allergens out of your body or off your skin. They can make you sneeze, tear up, or itch -- whatever it takes to get the job done. They are part of your body's defense system.

When you have allergies, some of your triggers -- such as pollen, pet dander, or dust -- seem harmless. But your immune system sees them as a threat and responds.

Your body's intention -- to keep you safe -- is good. But its overreaction gives you those all-too-familiar allergy symptoms, which you then try to stop with an antihistamine.

When you come across your allergy trigger, your immune system knows it and launches a chain reaction to defend you.

First, it sends a chemical signal to "mast cells" in your skin, lungs, nose, mouth, gut, and blood. The message is, "Release histamines," which are stored in the mast cells.

When they leave the mast cells, histamines boost blood flow in the area of your body the allergen affected. This causes inflammation, which lets other chemicals from your immune system step in to do repair work. Histamines then dock at special places called "receptors" in your body.

The result? If your nose was affected -- say by pollen -- histamines prompt thin walls, called membranes, to make more mucus. You can get a runny or stuffy nose. And you'll sneeze. The mucus can also bother your throat and make you cough. Histamines can make your eyes and nose itch.

If you have a food allergy, histamines are in on that response process, too. When you accidentally eat or drink something you shouldn't, they'll work in your gut to trigger your allergic reaction.

Some foods are also naturally high in histamines. These include aged and fermented foods and alcohol (especially red wine). Some people may be sensitive to that.

"Histamine poisoning" can happen if you eat fish that weren't kept at safe temperatures and spoiled before you got them. Those fish can build up high levels of histamines, which can make you sick. Doctors call this "scombrotoxin fish poisoning," or SFP. It's not likely to happen with good food safety practices.

Many plants and animals also have histamines. For instance, they're in some insect venom.

If you're stung or bitten by an insect, your own histamines will also kick in as part of your defenses -- in this case, because you really are under attack.