If you develop a stuffy nose or headache after eating certain foods, it may not be because of an allergic reaction. Instead, you could have a histamine intolerance—when the body simply cannot process high levels of this runny-nose-causing, congestion-inducing chemical.

This may sound a bit confusing, since histamine is best known as the chemical that the immune system produces when someone with an allergy is presented with something they are allergic to. However, histamine is also found in certain foods in high amounts, and some foods release histamine stored in the body.

Diet alone can cause histamine levels to rise so high that someone with histamine intolerance experiences allergy-like symptoms without having an allergic reaction. It's also possible for someone to have allergies and histamine intolerance.

This article covers what it means to have a histamine intolerance, how it differs from an allergy, and steps you can take to minimize your symptoms.

Allergy vs. Intolerance
An intolerance—to a food or a chemical—is different from a true allergy. An intolerance usually occurs when your body lacks certain enzymes needed to digest or process a substance. An allergic reaction occurs when your body's immune system identifies and attacks an allergen.

Histamine Intolerance Symptoms
The most common symptoms of histamine intolerance include:1

Migraine headaches
Digestive symptoms, such as diarrhoea
Flushed skin
Hives
Worsening eczema
Congested, runny, or itchy nose
Red, itchy, or watery eyes
The severity of symptoms can vary from person to person.

Because levels of histamine can build up in the body, people who have allergies in addition to a histamine intolerance can experience more serious allergic reactions. These can include asthma attacks or even anaphylactic shock—a dangerous, rapid reaction that causes breathing issues and a life-threatening drop in blood pressure.

Elevated levels of histamine can also cause the heart to beat erratically and may be associated with serious chronic conditions like Crohn's disease.2

Recap
Because both conditions are triggered by high levels of histamine, symptoms of histamine intolerance are similar to those of allergies. Symptoms can vary from person to person, and those with both conditions are most likely to experience serious reactions.

Causes
Research has shown that a small portion of people—about 1% to 3%—have a histamine intolerance.3

Your body makes two enzymes in order to process histamine: diamine oxidase (DAO) and histamine-N-methyltransferase (HNMT).

DAO comes from the digestive tract and HNMT comes from the central nervous system. People with histamine intolerance often have low levels of either of these enzymes, most commonly DAO.

Without enough of the right enzymes to clear histamine from the body and maintain healthy levels, it can build up and cause symptoms that can mimic allergies.1

Some people have genetic mutations that decrease the amount or function of DAO. There's some evidence that inflammatory bowel disease and gluten sensitivity can also affect DAO levels.3

Foods that contain histamine can also contain substances that temporarily block DAO. Alcohol and certain drugs, including some blood pressure drugs and acid blockers, can also reduce the enzyme's activity.3
Diagnosis
Diagnosing a histamine intolerance can be challenging. Like other chemicals in your body, levels of histamine shift based on the speed at which your body processes it.

Eating a high-histamine food (or more than one at the same time) may be enough to cause symptoms one day, but may not be enough to do so on a different day.
Testing is needed to help form a diagnosis—a process that includes, and may even start with, taking steps to rule out other possibilities.

Review of Symptom History
If you repeatedly experience symptoms after eating foods that are high in histamine, it may be helpful to keep a food log and review it with your healthcare professional.

A record of the foods you eat and any symptoms you develop can help you and your medical professional track the pattern of symptoms and determine whether specific foods may be to blame.

Tests to Rule Out Other Conditions
Coming to a histamine intolerance diagnosis is often a process of elimination. This may be because your healthcare provider mistakes a histamine intolerance for something else at first.

It may also be because other conditions are far more likely than histamine intolerance, making testing for other possibilities first more sensible.

Traditional allergy tests are not effective for diagnosing histamine intolerance. This includes skin tests that measure reactions when small amounts of allergens are injected or applied to small breaks (or pricks) in the skin.

However, your doctor may use these tests to make sure specific allergens aren't causing your symptoms.

Furthermore, studies have shown that histamine may play a role in inflammatory bowel disease (IBD) and irritable bowel syndrome (IBS).4

If you are experiencing gastrointestinal symptoms, such as diarrhea, your healthcare provider may run additional tests to rule these two conditions out.5

These tests could include:

Blood or stool tests
Imaging, such as an X-ray or computed tomography (CT) scan
Colonoscopy
Endoscopy of the upper gastrointestinal tract
DAO Testing
A blood test to check your DAO levels may be useful, as it can determine whether they are too low.
Histamine Challenge
If a histamine intolerance is suspected, your healthcare provider may recommend a test called a histamine challenge.

For this test, you're given a dose of histamine and monitored for a response. This type of challenge is performed in a clinical setting in case you have a serious reaction.6
Recap
Diagnosing a histamine intolerance can be difficult, and in many cases is a process of elimination. Keeping a food log to track your symptoms can be helpful. Your doctor may run tests to rule out other conditions, such as IBS or a true allergy. A histamine challenge may be helpful to confirm the diagnosis.

Treatment
Like an allergy, the best way to treat an intolerance is to avoid the substance—in this case, histamine. A histamine-free diet may be enough to make your symptoms go away.1

While a histamine-free diet is the only true long-term treatment for histamine intolerance, there are a couple of other options that can help you manage symptoms. These may be particularly useful for those whose symptoms are frequent and severe.
Diet: Foods to Avoid If You Have Histamine Intolerance
Avoiding histamine-rich foods, or foods that trigger your body to release histamine, is an important first step. Maintaining a strict low-histamine or histamine-free diet is the key to relief from histamine intolerance symptoms.1

Your healthcare provider will discuss which foods you should avoid. In general, fermented, aged, or processed foods have higher levels of histamine and are more likely to cause problems. Other foods, such as citrus fruits, can trigger your body to release stored histamine.7

Alcoholic beverages can be problematic for people who have histamine intolerance because alcohol can make DAO less effective.1 Therefore, giving up alcohol is part of a histamine-free diet strategy.

Antihistamines
Antihistamine medicines such as Benadryl (diphenhydramine) may be useful if you accidentally eat a food that contains histamine. These medications block histamine activity and can reduce symptoms.

There are multiple antihistamine medications available over the counter or by prescription. Almost all of them have side effects that can include drowsiness, urinary retention, constipation, and dry mouth.8

Talk to your doctor about which antihistamine is best for you.

Supplements
In addition to a modified diet, your healthcare provider may recommend using certain types of supplements to help reduce or eliminate your symptoms.9

A DAO supplement may be one option. Or they may suggest high doses of vitamin C, copper, or vitamin B6, all of which stimulate the activity of histamine-processing enzymes in the body.

Talk to your healthcare provider if you're interested in trying these supplements to see whether they could improve your symptoms.

Changes to Current Medications
Talk to your healthcare provider about any medications, prescription or non-prescription, you're already taking. Some medications can affect the action of your histamine-processing enzymes.

If you are taking such a medication, your healthcare provider may adjust your dosage, switch you to a similar medication that doesn't affect histamine, or take you off the medicine entirely if it's safe to do so.

Recap
The best histamine intolerance treatment is avoiding foods that contain or encourage high levels of the chemical. Your doctor may also recommend using certain supplements to increase histamine-processing enzymes or antihistamines to ease symptoms.

Summary
If you frequently experience allergy symptoms after eating high-histamine foods like beer or wine, sauerkraut, or even certain cheeses, it's possible that you may have an intolerance to histamine instead of a food allergy.

The best way to treat an intolerance is avoidance. By not eating foods that contain histamine or prompt your body to release it, you can take control of your symptoms. Talk with your doctor about whether you should also consider an antihistamine medication or an enzyme-boosting supplement.

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