What Is Mast Cell Activation Syndrome?

Dr. Franklyn R. Gergits, MBA, DO, FAOCO · Board-Certified Otolaryngologist · Fellowship-Trained Otolaryngic Allergist · 30+ Years of Experience · Clinical Focus in Rhinology and Airway Disorders

Short answer: Mast cell activation syndrome is a condition where immune cells called mast cells release their contents when they shouldn’t. Those cells are present throughout your body but concentrated in the skin, the airway, the cardiovascular system, and the digestive tract. When they release, out come histamine, tryptase, and other immunomodulators, and you get symptoms like cough, wheeze, flushing that often comes with a racing heart, a diffuse whole-body rash, hives, diarrhea, cramping, and lightheadedness. Nasal congestion and post-nasal drainage may be part of the picture too. The reaction itself is normal — every one of us needs mast cells. What makes it a syndrome is that a reaction which is supposed to be tightly controlled starts happening intermittently, without a good reason, and hits more than one system at a time.

Patients bring me this term now. They have read about it somewhere, they do not really understand what it is, and what they actually want to know is whether it explains what has been happening to them.

So let me answer the question directly, and then tell you how I decide whether it applies to a particular person sitting in my exam room in Scottsdale.

What Mast Cells Are, and What They Are Doing

Mast cells are immune cells. They are everywhere in your body, but they concentrate in four places: your skin, your airway, your cardiovascular system, and your digestive system. Notice that those four places are exactly where the symptoms show up. That is not a coincidence — it is the whole explanation.

When a mast cell degranulates, it releases its contents. Histamine, tryptase, and a range of other immunomodulators go into the surrounding tissue. Those chemicals are what produce the symptoms.

Here is the part that matters, and it is the thing patients most often get wrong. This is a normal process. You need mast cells. They are part of how your body defends itself. The problem in MCAS is not that mast cells exist or that they release — it is that a reaction which is normally very tightly controlled starts happening intermittently, without a proportionate trigger.

The Way I Explain It

Think of it as a snowball rolling off a high mountain that has the potential to cause an avalanche.

The snowball itself is nothing. A small trigger, something that should not amount to much. But it gathers mass on the way down. And the danger was never the snowball — it is what it becomes by the time it reaches the bottom, and how much it takes with it.

That is why the symptom list is so long and so scattered. An avalanche does not hit one thing.

Who Actually Gets This

I want to be straightforward here, because there is a great deal written about MCAS online and much of it leaves the impression that this is everywhere.

Primary MCAS — the idiopathic form, where the mast cells are abnormal and we have no idea why — is rare. That is the honest answer.

The secondary form is different. There the mast cells are normal and healthy, and they are degranulating in response to a stimulus: a food, stress, an infection, an autoimmune disease. The cells are behaving the way cells behave. Something is setting them off.

As for who: females in midlife are the highest percentage by a clear margin. That does not mean nobody else gets it. It means that when I am weighing probability, that is part of the picture.

How I Decide Whether It Is You

This is the part patients care about most, so here is my actual reasoning.

What I am looking for is multi-system involvement. Flushing or hives. Lightheadedness. Cough. Stomach cramping or diarrhea. If I am getting a combination from two different systems, happening indiscriminately, then I start thinking about mast cell activation. One system alone does not get me there.

And there are several other conditions that produce overlapping complaints, which is exactly why the nose alone is not enough:

Posterior nasal nerve overactivity. If someone has posterior nasal drainage and congestion and none of the other symptoms, I am thinking PNN, not mast cells.

Non-allergic rhinitis. Similar to PNN in how it presents, but with more anterior symptoms rather than purely posterior ones. That distinction is small and it matters.

Laryngopharyngeal reflux. LPR is the tough one, because it can itself cause mast cell degranulation in both the gut and the airway. So it is not always a question of which one you have. Reflux can be the stimulus driving the mast cell response.

Posterior Sinonasal Syndrome. PSS is the working hypothesis I have spent years developing — pepsin reaching the posterior nasal mucosa through silent extraesophageal reflux, driving inflammation upstream of what a CT scan will show. PSS sits with MCAS or against it depending on the patient. Sometimes they are separate processes. Sometimes one is feeding the other.

Which is why my question is always the same: what else is happening, and can I decrease the frequency with daily H1 and H2 blockade? That trial is not just treatment. It is information.

If You Have Been Told It Is Anxiety, IBS, or Stress

Some patients arrive already convinced they have MCAS and braced for one more physician who does not believe them. They have been handed anxiety, IBS, stress, idiopathic — a series of labels that explain nothing.

My answer is that it could be any of those things. But it could also be a combination of all of them, all affecting the mast cells.

Those explanations were never mutually exclusive. Stress is a documented mast cell trigger. Gut inflammation and airway inflammation are connected. The problem with the labels was not that they were wrong — it is that each one was handed over as though it were the whole answer, when the actual picture involves several things acting on the same cells at once.

What To Do If You Think This Is You

Come see someone who can shed light on it. That is the first step, and it is not a small one — a great deal of what makes this condition miserable is being passed between specialists who each look at one organ.

Here is what the evaluation looks like. We screen. We get a baseline tryptase, and we provide a standing order so you can obtain a blood draw as soon as possible after symptoms begin. If more than two hours have passed, we do not force it — we wait for the next episode and try again. That order stays with you.

What to bring: any allergy testing results you already have, and a symptom diary.

I ask patients to track symptoms and when they occur, triggers, what was happening at the time, stress levels, sleep, diet, exposures, and frequency. And critically: what helps and what does not. That diary frequently tells me more than any single lab value, because it captures the pattern, and the pattern is the diagnosis. Patients throughout Scottsdale, Phoenix, and Maricopa County who arrive with a real diary get further in one visit than patients who arrive with a stack of normal test results.

What I Want You To Take Away

If you remember one thing from this six months from now, I hope it is that you have been symptom free.

Comforted with knowledge, and hopefully with a true diagnosis. That is the goal — not a label, but an actual explanation and a set of symptoms that no longer runs your life.

People Also Ask

Is MCAS common?
The primary, idiopathic form is rare. The secondary form, where normal mast cells degranulate in response to a stimulus like food, stress, infection, or autoimmune disease, is what I encounter more often. Midlife women make up the highest percentage.

Can MCAS cause nasal congestion and post-nasal drainage?
Yes, and mast cells are present in the nasal lining. But congestion and drainage alone will not get me to the diagnosis. If those are the only symptoms, I am thinking about posterior nasal nerve overactivity or non-allergic rhinitis first.

What is the difference between primary and secondary MCAS?
In primary MCAS the mast cells themselves are abnormal and we do not know why. In secondary MCAS the cells are normal and healthy and something is triggering them — a food, stress, an infection, an autoimmune condition. Finding the stimulus is the work.

Does responding to antihistamines mean I have MCAS?
Not on its own. A trial of H1 and H2 blockade is genuinely useful information, and reduced symptom frequency points somewhere. But several forms of rhinitis improve on antihistamines, so the response has to be read alongside the multi-system pattern and the objective testing.

Want to Understand More

→ Is It Allergies or MCAS? How an ENT Tells the Difference

→ Why Do Allergy Symptoms Keep Changing — and Nothing Works?

→ Is Mast Cell Activation Syndrome the Reason Your Sinuses Never Fully Clear?

→ What Is NEUROMARK, and Could It Stop Your Chronic Drainage?

→ The Final Chapter — What the Field Still Has Not Explained

→ The Airway & Sinus Wellness Review

About the Author

Dr. Franklyn R. Gergits, MBA, DO, FAOCO is a Board-Certified Otolaryngologist and Fellowship-Trained Otolaryngic Allergist with a Clinical Focus in Rhinology and Airway Disorders and over 30 years of clinical experience, first at Northeast Ear Nose and Throat Associates in Berwick and Bloomsburg, Pennsylvania, and now in Scottsdale. He is the founder of the Sinus & Allergy Wellness Center of North Scottsdale, where he performs in-office balloon sinuplasty, turbinate reduction, NEUROMARK® posterior nasal nerve ablation (Neurent Medical, FDA-cleared radiofrequency ablation system), and Eustachian tube dilation under local anesthesia. He performed the first balloon sinuplasty in Pennsylvania and earned dual Entellus Centers of Excellence certifications. Dr. Gergits is the originator of the Posterior Sinonasal Syndrome (PSS) hypothesis — a clinical framework identifying pepsin-mediated posterior nasal mucosal injury as an upstream driver of chronic rhinosinusitis. Preprints available at Preprints.org (PSS: DOI 10.20944/preprints202603.0858.v1 · Mucosal Liquid Layer: DOI 10.20944/preprints202605.0727.v1). ORCID: 0009-0000-4893-6332.

SinusAndAllergyWellnessCenter.com · 480-525-8999

This content is for educational purposes only and does not constitute medical advice. Mast cell activation syndrome is a complex diagnosis that requires individualized evaluation, and any laboratory testing described here must be ordered and interpreted by a qualified physician in the context of your full history. If you are experiencing symptoms involving more than one organ system, please seek evaluation from a qualified physician for individualized recommendations.