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Why Does MCAS Get Confused with Histamine Intolerance?

Updated: Mar 15

In a recent post we discussed how histamine intolerance differs from other intolerances because histamine gets into the blood stream and can impact any part of your body.

Once it is in your bloodstream, it can bind to histamine receptors in any cell, anywhere in the body.

It is through this action of binding to cell receptors that histamine has such a profound impact on a wide variety of tissues.

The binding of histamine to immune cells such as mast cells can be problematic for some people. This is where things can get tricky. Keep reading to find out how mast cells are impacted by histamine from food.

Histamine Binding is a Good Thing

Histamine is necessary for human health. It works by binding to histamine receptors found on cells in the body. Refer back to this blog article featuring an excerpt from our book, explaining how histamine is a key, and receptor sites are the lock. We have these 'locks' in every organ and system in the body.

It should come as no surprise then that histamine has the potential to affect every single organ and system in the body!

Histamine & inflammation & protecting your body

Histamine is an integral component of at least twenty-three different physiological actions in the body. They are the body's response to an inflammatory crisis, inducing signalling blood vessels to become permeable in order to release the immune system's defence team.

This helps to protect your body against foreign invaders. Think about when you cut your finger—histamine release is part of the immune system's defense mode to help flood the injured area with fresh blood, carrying your immune system's cleanup crew to neutralize potential infections or harm.

Histamine & the brain

Histamine performs key stimulatory tasks in the brain as well. It acts as a neurotransmitter in maintaining circadian rhythms. This is your body's inner 24-hour clock and governs your sleep/wake cycle.

Histamine is also part of the hypothalamus's signalling system, to turn the fight or flight mode on and off.

Histamine also influences libido and sexual arousal in all genders.

Histamine & digestion

In addition, histamine stimulates the stomach lining to produce hydrochloric acid to break down the foods you eat, so that you can absorb the nutrients within.

It initiates all these actions by binding to histamine receptors on cells.

When Histamine Binding Goes Awry

Histamine can bind to mast cells as well.

With Mast Cell Activation Syndrome (MCAS), the mast cells are hyper-reactive or sensitized and will react more strongly with less stimuli than normal.

This sensitivity means that the normal action of histamine binding to mast cells results in an inappropriate or excessive release of chemical mediators.

Mast cells mistakenly or inappropriately release chemical mediators resulting in inflammation and the vast profile of symptoms individuals experience.

The symptom profile is unique to each person, so that you may have a few symptoms, or you may have many symptoms. These symptoms can range from mild to severe.

Histamine from foods can result in this cascade.

This is the reason that MCAS and histamine intolerance can get confused. And to add to the

confusion, you can have both conditions.

Looking forward

A low histamine diet can be a good starting place for many individuals struggling with MCAS. The problem now is that mast cells can be sensitized to other compounds and substances in food as well.

This is where the invitation becomes to don that detective hat, and do some deeper searching in order to figure these out for you as an individual.

That’s why our Histamine Haven Shopping List looks different from other low histamine lists. We have removed other triggers such as lectins and molds as well. Our cookbook also features recipe variations if oxalates, salicylates, or autoimmune triggers are a problem for you.

Which Condition Do You Have?

If you have tried a low histamine diet and supplemented with DAO and your symptoms go away, it is likely you have histamine intolerance.

If you see an improvement in some of your symptoms, but are still struggling to manage them, it is worth exploring other reasons for your symptoms, including MCAS.

There are many other triggers for MCAS (in addition to the food ones). Working with a skilled practitioner is important to help you identify what are your individual triggers.

Next Steps

  1. Try a low histamine diet. Download our full Shopping List here.

  2. Add a DAO supplement.

  3. Monitor your symptoms.

  4. Feeling better? It’s still important to figure out if your DAO deficiency is genetic, from leaky gut, or an inflammatory bowel disease. Hint: The usual recommendation to consume bone broth for leaky gut will make your symptoms worse.

  5. Noticing a small change? It’s important to figure out what is going on. Start by visiting your family doctor and asking for a referral to an immunologist or allergist who is familiar with MCAS.


Curious to understand this histamine or MCAS distinction a little deeper? Consider joining us at our next The Histamine Connection class. It's a free class we host online every month or so, and it's the perfect place to start.

In the class, we'll help you make that histamine connection for yourself, and get you started on solutions to reduce what's driving your symptoms. Register for the next class by visiting this page.  Let's get you feeling better!

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