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Histamine Intolerance: Not As Simple As Allergies

Person blowing their nose from histamine intolerance

It's suggested that between 1% and 4% of the population has a histamine intolerance. This condition often looks like a food allergy, but most food allergy tests can't detect it. People with histamine intolerance deal with a barrage of unexplained symptoms, often effecting digestion, that don’t make much sense to them and their health care providers, but continue to make life pretty difficult.

In the 20 years I’ve spent in functional medicine I’ve realized two things:

  1. People are unaware that histamine intolerance is actually a thing (although this is slowly changing).
  2. Primary care physicians, on a whole, ignore or leave many people who have the common signs and symptoms of this intolerance undiagnosed because there isn't much data on this condition.

Diagnosing histamine intolerance has become a bit like Hansel and Gretel finding their way in the woods. Before a clinician can decisively say you're dealing with an intolerance, they have to follow the trail of breadcrumbs that lead them to the source of your symptoms. This is exactly what we do in root-cause-focused Functional Medicine.

Of course, when you’re feeling tired, breaking out in hives, having unexplained flatulence, gas, bloating and diarrhea - even headaches with greater frequency - you know there’s something wrong. If only knowing what was wrong was as easy as knowing something is wrong, we'd all be a lot healthier!

That said, without the right diagnosis, you won’t know for certain if histamine is the culprit or if it’s something else entirely.

What Is Histamine?

Histamine has 23 physiological functions in the body and is one of the most studied biomolecules. Although it has an essential role in our wellbeing it's also starting to make us feel terrible. Why is that? To truly understand why histamine intolerance can be misunderstood and overlooked -- while having such widespread (and crappy) symptoms -- you need to understand what histamine does.

Histamine is essential to three things:


It is a key component in stomach acid that aids in proper digestion. Too much histmaine

Neurological function

Histamine acts as neurotransmitter in the brain and spinal cord.

Responding to allergic reaction

It is the first responder in allergic reactions. Histamine sends inflammation to dilate blood vessels so white blood cells can reach and neutralize invaders.

What’s Causing Your Histamine Intolerance? Histamine Etiology

Histamine intolerance isn't actually an intolerance to histamine.

Everyone has histamine in their gut and nervous system (it's a naturally occurring entity). It’s also common in food, so you're likely ingesting histamine regularly.

Thus, what most doctors refer to as an intolerance could be more accurately described as an overload.

Here, your body is reacting to a build up of the biomolecule in your bloodstream and gut. It’s also not something that happens quickly. The onset of symptoms can be gradual and usually correlates with the amount of  histamine in your body.

When the histamine content increases in your body, so do the symptoms - symptoms that commonly mimic those of food allergies.

If you had one small rock in your shoe, it would be annoying but maybe not a big deal. Add a fistful of tiny pebbles, one at a time, and eventually it would be super annoying and you’d have to stop and deal with the symptoms of rocks in your shoe - pain and inflammation in your poor foot. That’s what a histamine intolerance is like: kinda sneaky, creeping up on you until the symptoms are too much to handle.

Three Common Causes of Histamine Intolerance

This is where you've got to start looking for breadcrumbs as they'll help you discover the underlying cause or causes of your condition. To do this, we need to take a closer look at your health and lifestyle. In most cases, histamine intolerance can be attributed to the following, as these things can trigger a build up of histamine in your body:


Yes, your meds are making the list (again).

  • Side effects are common in many OTC and prescribed medications, and these can include histamine intolerance.
  • The medication doesn't directly cause an intolerance but it does decrease your capacity to degrade, or break down, histamine.
  • Your body degrades histamine in one of two ways: N-Methyltransferase (HMT) for the histamine in your central nervous system and diamine oxidase (DAO) to metabolize the histamine in your gut.
  • When medication blocks the production of DAO, you're essentially causing the histamine in your system to build up which is responsible for the symptoms you'll experience.

Over the counter and prescribed medication often have DAO blockers.

These medicines** include:

  • Antihistamines
  • H2 Histamine Blockers
  • Antiarrhythmics
  • Antipsychotics and antidepressants
  • Non-steroidal Anti Inflammatory drugs (NSAIDS)
  • Immune modulators

Gut Health

The science isn't definitive on whether gut health directly (or indirectly) affects histamine levels. However, the idea is starting to gain traction in the western medical world, although it could be awhile before it's fully explored.

I do think it’s worth mentioning as the two are so closely related. As I've learnt over decades in my own practice, many patients who experience histamine overload will either have a diagnosed or undiagnosed gastrointestinal issue.

This includes IBS, SIBO, Crohn’s disease and Leaky Gut Syndrome, amongst other issues.

I see a lot of histamine intolerance with SIBO due to the changes in the composition of the gut microbiome. In other words, the good bacteria that help keep histamine in check are no longer able to do their work. Since the metabolism of histamine is directly affected by enzymes (DAO) in your gut, any imbalance (whether seemingly unrelated) could cause a ripple effect.


If you already have a lot of histamine in your system and add in high histamine foods that your gut can’t process out, you’re likely to have histamine symptoms. These aren’t the usual unhealthy foods you’ve been told to avoid. These can be (and likely are) food you’ve been told to eat as part of a healthy diet.

Honestly, histamine is common in most food. That’s why symptoms can persist for quite some time without any obvious “trigger." However, diet has another role in developing an intolerance to histamine.

Certain food also has the ability to block the production of DAO. When you're combining a diet high in DAO blockers and elevated histamine due to a gut imbalance or using one of the medications above, an intolerance is a logical outcome.

Histamine Intolerance Symptoms

The trail of breadcrumbs continues! The next thing to do is to take a look at your symptoms and see if there are any of these that could be attributed to a histamine intolerance.

These are the most common symptoms associated with the condition:

  • Irritable Bowel Syndrome symptoms
  • Bloating, intestinal gas, which can mimic or coincide with SIBO
  • Hives
  • Abdominal Cramps
  • Abnormal Menstrual Cycle and Cramping
  • Acid Reflux
  • Indigestion
  • Itching, especially if you look at the itchy skin and there’s no rash or anything visible there as the cause of itching
  • Accelerated Heart Rate
  • Inflammation or Swelling
  • Headaches
  • Fatigue
  • Diarrhea
  • Vertigo or Dizziness
  • Panic Attacks
  • Difficulty Sleeping
  • Sinus Issues (Sneezing, and nasal congestion)
  • Low Blood Pressure

The Difference Between Histamine Intolerance and Allergies

Most individuals with a histamine intolerance may think it's nothing more than a mild food allergy. Since so many symptoms overlap, the idea that you’re dealing with “just a food allergy” is usually substantiated by your body's reaction to food you’re eating that have a high histamine content.

Keep in mind, however, that histamine is the key ingredient in both allergic reactions and histamine intolerance symptoms.

However, those with an intolerance aren't allergic to the food that triggers their symptoms. Instead, what they have is either a lack of DAO (the enzyme that metabolizes excess histamine) in their gut, or have far too much histamine in their body -- or both.

The primary difference between the two (in relation to their symptoms) is the severity of the symptoms and for how long you have the reaction. Histamine intolerance symptoms won't be as severe as an allergic reaction in most cases. Although many of the symptoms experienced with a histamine intolerance are common in typical food allergies, histamine symptoms usually persist, becoming a part of your daily life.

Testing For Histamine Intolerance

As histamine intolerance isn't widely acknowledged, studied or emphasized in the medical community, there are few tests for an intolerance to histamine. Most tests involving histamine focus on allergies instead of build up. However, there are a few tests that can help determine with greater levels of accuracy if you are in fact histamine intolerant.

Some commonly suggested tests include:

The Skin Prick Test

This simple, inexpensive test has been suggested to determine whether someone is indeed histamine intolerant. Using a needle, an allergist will either prick or scratch the surface of the skin and then apply a histamine solution to the skin's surface. They then wait until a wheal (raised bump under the skin) appears, usually followed by determining how quickly it appeared and how long it remained elevated in order to diagnose an intolerance.

Serum Diamine Oxidase Test

This test measures the level of Diaminoxidase (DAO) in your bloodstream. If you have a histamine intolerance, the level of diamine oxidase (DAO) present in your blood will be lower than lab normals.

Serum Tryptase Test

Instead of determining whether you have histamine intolerance, a serum tryptase test can help you rule out other possible causes of your symptoms.

In this test, your provider will be able to rule out an increased burden of mast cells as the cause of your symptoms. Mast cells are responsible for releasing histamine. The symptoms of mast cell elevation can look like elevated systemic histamine, and this test can help determine if you’re dealing with one or the other.

Beyond Lab Testing

Any test can have false positives or negatives, so it's important for your healthcare provider to analyze your case holistically. To be real, none of these tests are a slam dunk. A smart and experienced clinician is adept at pattern recognition, a skill that I find most useful when it comes to histamine intolerance.

Elimination Diet

The best test, in my experience, is an elimination diet. This can help give us a good idea of the intolerance and its extent. Changes to your diet continue to be the most accurate method of determining whether you have a histamine intolerance. It's the simplest (and cheapest) test of them all.

To conduct this test, you'd start by eliminating histamine rich food and beverages from your diet. Document any changes over time. In many cases, those without a histamine intolerance won't experience any significant change in their symptoms.

Where do we go from here?

As histamine intolerance gains traction in the medical community, hopefully so too will conclusive (affordable) testing. While we wait for that to happen, making simple changes to our diet to cutback on histamine rich food and DAO blockers can be a very effective recourse.


**As always, before discontinuing the use of any of the aforementioned medication you need to consult with your PCP. There are more holistic approaches for many common medical concerns that could reduce or eliminate the symptoms of histamine intolerance without nasty side effects.

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  1. Denise Solomon on December 16, 2019 at 8:29 pm

    Hi Ms. Albina !
    Could you clarify a point? Do antidepressants like Escitalopram block DAO ? I developed a really bad Histamine intolerance – out of the blue in my 60’ies – could antidepressants have cause it ?

    thanks , Denise

    • Victoria Albina on December 17, 2019 at 10:59 am

      Hello Ms. Solomon! (keeping with the formal salutation trend here ;),

      SSRIs have been shown to *improve* histamine clearance. That said, they can have negative effects on the gut microbiome, which could be leading to histamine issues. I would recommend anyone with histamine intolerance work with a Functional Medicine provider to get to the root cause of both the histamine issues and here, why one might want to be on SSRIs. I also highly recommend Johann Hari’s book “Lost Connections” which is about SSRIs, depression and anxiety in our modern world – an excellent read. (Note: please buy your books from your local, family-owned independent bookseller!!)

      All the best! – Victoria