Why Do I React to Everything? Part Two: MCAS vs. Histamine Intolerance

I am a remarried woman.

I'm talking about my physicians, of course. Not my actual husband. I love him. We've been together since we were 17 and have no intention of letting each other go.

Doctors—and the other people I hire to help me with my health—however, are a different story.

It's important to find a physician, health coach, personal trainer, or other professional who is going to listen to what you're saying, educate themselves to best help you navigate your health, and support you through the hard times.

With that in mind, I go back to my previous statement:

I am a remarried woman.

I found not only one, but two great physicians and a personal trainer to refer to when I'm stuck or struggling to overcome the next hurdle in my healing journey.

Because let's face it: healing isn't linear.

It's messy.

It looks a lot like my nine-year-old's bedroom because nobody prepared me to raise a girl whose purpose in life is apparently to go through as many press-on nails as she can.

Just when I think I have them all cleaned up, I find more stuck in the carpet, on the kitchen table, and in my shower.

Much like recovering from chronic illness, it happens in phases. You have good days. You have bad days. You make progress, hit another hurdle, learn something new, and adjust.

But I like to think that a 1% improvement at each phase will eventually get you to 100%.

And part of making that 1% improvement is understanding what's actually happening in your body.

Chronic illness can involve many different contributing factors. Understanding the differences between symptoms and the mechanisms behind them can help us start chasing down what may be contributing to the problem—and hopefully find some relief along the way.

Is it MCAS?

Histamine intolerance?

Can it be more than one?

And how do we start figuring that out?

A Quick MCAS Review

We covered MCAS in the last post, but let's do a quick review.

Mast Cell Activation Syndrome involves excessive or inappropriate mast-cell activation, resulting in an overactive immune response.

Mast cells are immune cells designed to protect us. When they sense a threat, they activate and release—or, scientifically, degranulate—chemicals that help stimulate and coordinate an immune response.

One of those chemicals is histamine.

This is a protective mechanism.

We want our mast cells to respond when something is actually threatening us.

The problem with MCAS is that mast cells can become overly reactive, releasing their chemical mediators when they shouldn't or responding disproportionately to a trigger.

When this happens, we can experience symptoms like hives, digestive distress, flushing, rashes, heart palpitations, headaches, congestion, insomnia, and many others.

And because there are so many potential triggers for mast-cell activation, narrowing down why someone's mast cells are so reactive can be complicated.

But What About Histamine?

I always hear about histamine when people talk about MCAS.

So what exactly is it?

Histamine is one of the chemical mediators released by mast cells. It plays several normal roles in the body, including helping coordinate immune and inflammatory responses.

Think about your nose getting stuffy when you're exposed to an irritant.

Histamine contributes to swelling, mucus production, itching, and sneezing. These reactions are part of the body's attempt to protect itself and get rid of something it perceives as a threat.

Histamine isn't inherently bad.

The problem is when the amount of histamine we're dealing with exceeds what our body can comfortably manage.

And this is where I like to use my stress-bucket analogy.

Imagine Your Body Has a Bucket

Imagine you have a bucket representing everything your body is trying to manage.

Diet. Social and emotional stress. Sleep. Exercise. Purpose. Light exposure and circadian rhythm. Illness, inflammation, and other physiological stressors.

And yes—histamine.

Our bodies continuously manage what's going into that bucket through normal physiological functions.

Ideally, we're managing the load while more gets added.

But what happens when we're adding things faster than the body can manage them?

Eventually...

the bucket overflows.

Flare.

Symptoms.

Discomfort.

For someone with MCAS, excessive mast-cell activation can dump even more mediators—including histamine—into an already-full bucket.

This is also one reason allergy medications can help.

Antihistamines don't necessarily stop mast cells from activating. Instead, H1 and H2 antihistamines block histamine receptors, preventing histamine from producing some of its effects after it has already been released.

Mast-cell stabilizers like cromolyn sodium work differently. Cromolyn helps inhibit mast-cell degranulation and the subsequent release of histamine and other inflammatory mediators.

But neither explanation answers the question that became increasingly important to me:

Why does the bucket keep getting so full in the first place?

So How Is Histamine Intolerance Different?

Here's where things get interesting.

You don't necessarily need excessive mast-cell activation to end up with too much histamine.

Histamine intolerance is more of a supply-and-clearance problem.

Histamine is coming in or being produced, but the body isn't breaking it down quickly enough.

Histamine accumulates.

The bucket gets fuller.

Eventually, it spills over.

And those symptoms can look a lot like MCAS:

Flushing. Migraines. Congestion. GI distress. Itching. Heart palpitations.

Sound familiar?

That's what makes this complicated.

With MCAS, mast cells are excessively or inappropriately activating and releasing histamine along with many other chemical mediators.

With histamine intolerance, the problem centers more around how much histamine the body is dealing with compared with how effectively it can break it down.

And yes, these problems can overlap.

Meet DAO

One important player in all of this is an enzyme called DAO, or diamine oxidase.

DAO helps break down extracellular histamine, particularly the histamine we encounter through the digestive tract.

DAO is produced in high concentrations by mature intestinal cells, which means gut health matters when we're talking about histamine metabolism.

If the intestinal environment is inflamed or the intestinal lining and microvilli are damaged, DAO activity may be affected. Dysbiosis and other GI issues may therefore become important pieces of the puzzle when someone isn't handling histamine well. Research has linked compromised intestinal mucosal integrity with reduced DAO activity, and emerging evidence also connects intestinal dysbiosis with histamine-producing bacteria and potentially altered DAO activity.

DAO can also be measured through laboratory testing. Like most functional markers, however, I don't want to look at one number in isolation.

If DAO is low, my next question is:

Why?

That's the question I became obsessed with asking about my own health.

And Yes, We're Talking About Leftovers

Do you eat leftovers?

I do.

But leftovers are usually higher in histamine than that same food was when it was freshly prepared, particularly with histamine-prone foods and depending on how they're stored.

As food sits, microbial activity can contribute to the production of histamine and other biogenic amines. Storage time, temperature, the particular food, and the microorganisms present all influence how much of these amines accumulate.

So imagine that your body is already struggling to clear histamine efficiently.

Then you eat a high-histamine meal.

More goes into the bucket.

And suddenly:

Flushing. Migraine. Congestion. Heart palpitations. GI distress.

Maybe you don't sleep well that night.

It looks an awful lot like a mast-cell flare.

But the mechanism behind it may not be exactly the same.

And recognizing that distinction changed the way I started looking at my own health.

That's Where FDN Came In

For a long time, I knew what I had been diagnosed with.

I knew what medications could help control my symptoms.

I knew some of my triggers. I had my rescue meds.

But I still had one question:

Why does my bucket keep filling up in the first place?

That's eventually what led me to Functional Diagnostic Nutrition® (FDN).

FDN didn't teach me to chase every individual symptom.

It taught me to start asking better questions.

What's happening with digestion? Why did this happen? What disrupted the normal function?

What does someone's history tell us?

How are they sleeping?

What are they eating?

How are they exercising?

What stressors are present?

What patterns can we find?

What can intentional functional lab testing tell us?

And when does something need to go back to a physician or another qualified healthcare professional?

Instead of looking at one symptom in isolation, I started looking at the whole picture.

And suddenly, my health started to make a little more sense.

That's Also How I Approach My Clients

This experience changed more than the way I approach my own health.

It changed the way I wanted to help other people.

When a client tells me they're exhausted, bloated, reacting to foods, struggling with sleep, dealing with headaches, or just generally feel like their body has turned against them, I don't want to immediately jump to:

“Here's a supplement for that symptom.”

I want to get curious.

What else is happening?

What happened before this started?

What patterns are showing up?

What might be filling their bucket faster than their body can manage it?

And what pieces of the puzzle haven't we looked at yet?

As an FDN Practitioner, I don't diagnose or treat MCAS, histamine intolerance, or other diseases. That's the role of your physician and medical team.

My job is to look for patterns and hidden stressors that may be contributing to dysfunction, use appropriate functional testing when it makes sense, and help clients build the diet and lifestyle foundations that support the body's normal physiology.

Because sometimes the symptom screaming the loudest isn't the beginning of the story.

It's just the ripple that finally got our attention.

One Piece at a Time

I still have MCAS.

I still have things I'm working through.

I still have good days and bad days.

And every once in a while, I find another proverbial press-on nail hiding in the carpet just when I thought I finally cleaned them all up.

That's healing.

Messy. Nonlinear. Individual.

But now I have better questions to ask, a team of people I trust when I need help, and a framework that helps me keep looking upstream instead of only chasing the newest symptom.

And if you don't have a physician who listens to you, takes your concerns seriously, and is willing to support you as you navigate your health?

Divorce them.

I'm serious.

You deserve a healthcare team that you're comfortable working with. Find someone who will listen, communicate, and work with you—not someone you're afraid to ask questions.

And if you need some referrals, let me know. I've been remarried enough times to have a few good ones. 😉

I'll keep doing this the same way I've been doing it:

1% at a time.

Because eventually, those little improvements become something much bigger.

And apparently, I'll keep finding press-on nails too.

Sources & Further Reading

American Academy of Allergy, Asthma & Immunology (AAAAI). Mast Cell Activation Syndrome (MCAS). Overview of mast-cell mediators, symptoms, testing, and diagnostic criteria.
AAAAI — Mast Cell Activation Syndrome

Weiler, C. R., et al. (2019). AAAAI Mast Cell Disorders Committee Work Group Report: Mast cell activation syndrome (MCAS) diagnosis and management. Journal of Allergy and Clinical Immunology, 144(4), 883–896.
AAAAI — MCAS Diagnosis and Management Work Group Report

National Center for Biotechnology Information (NCBI), StatPearls. Cromolyn Sodium. Overview of cromolyn as a mast-cell stabilizer and its inhibition of mast-cell degranulation and mediator release.
NCBI Bookshelf — Cromolyn Sodium

Comas-Basté, O., et al. (2020). Histamine Intolerance: The Current State of the Art. Biomolecules, 10(8), 1181. Reviews histamine metabolism, DAO, intestinal DAO activity, dietary histamine, and factors associated with impaired DAO activity.
PubMed Central — Histamine Intolerance: The Current State of the Art

Hrubisko, M., et al. (2021). Histamine Intolerance—The More We Know the Less We Know. A Review. Nutrients, 13(7), 2228. Reviews DAO production in the intestinal epithelium and the proposed role of impaired histamine degradation in histamine intolerance.
PubMed Central — Histamine Intolerance Review

Evidence for Dietary Management of Histamine Intolerance. Reviews DAO production by mature intestinal enterocytes, intestinal mucosal integrity, dysbiosis, histamine-producing bacteria, and dietary approaches to histamine intolerance.
PubMed Central — Dietary Management of Histamine Intolerance

Durak-Dados, A., et al. (2020). Histamine and Other Biogenic Amines in Food. Journal of Veterinary Research, 64(2), 281–288. Reviews histamine and other biogenic amines in foods and the effects of microbial activity, processing, temperature, and storage.
PubMed Central — Histamine and Other Biogenic Amines in Food

This article is for educational purposes and is not intended to diagnose, treat, cure, or prevent disease. Individual symptoms can have many possible causes. Work with an appropriately licensed healthcare professional for diagnosis and medical treatment.