Hi Friend
Over the years I have spoken with thousands of people who share a remarkably similar story. Years of symptoms. Dozens of appointments. Normal test results. Being told it is anxiety, or stress, or just one of those things. And all the while knowing, with absolute certainty, that something is genuinely wrong.
If that sounds familiar, this series of emails is for you.
Over the next five emails I am going to walk you through everything you need to know about a condition called Mast Cell Activation Syndrome, or MCAS. What it is, why it is so often missed, how it is diagnosed, how it is treated, and what you can do about it right now. By the end I want you to have a clearer picture of your own health than you have ever had before.
Let's start at the beginning.
So what exactly are mast cells?
Mast cells are a type of immune cell. They live in almost every tissue in your body, particularly in places that interface with the outside world, your skin, your gut, your lungs, your nasal passages, and your blood vessels. Their job is to act as sentinels, standing guard and ready to respond when the body encounters something potentially threatening, whether that is an infection, an injury, an allergen, or a toxin.
When a mast cell detects a threat, it activates and releases a cocktail of chemical mediators, the most well known of which is histamine. These chemicals trigger inflammation, increase blood flow to the area, attract other immune cells, and essentially sound the alarm throughout the body. In the right circumstances this is a brilliantly effective defence mechanism. It is how your body fights infections and heals wounds.
The problem begins when mast cells become dysregulated.
What happens when mast cells go wrong
In Mast Cell Activation Syndrome, the mast cells become unstable and hypersensitive. They start firing off inappropriately, releasing their chemical mediators in response to triggers that should not cause any reaction at all. Things like certain foods, temperatures, fragrances, stress, hormonal changes, exercise, or even just changes in position.
Because mast cells are present throughout the body, when they misbehave the symptoms they cause can affect virtually every organ system simultaneously. This is the defining and most confusing feature of MCAS. It does not look like one condition. It looks like many conditions happening at the same time.
What does MCAS actually feel like?
This is where it gets interesting, and where so many patients finally have their lightbulb moment.
MCAS symptoms span an extraordinary range. Skin symptoms like hives, flushing, itching, and rashes that come and go without obvious cause. Gut symptoms like bloating, nausea, abdominal pain, diarrhoea, and reflux. Cardiovascular symptoms like a racing or irregular heart rate, dizziness on standing, and low blood pressure. Neurological symptoms like brain fog, headaches, poor concentration, and memory problems. Respiratory symptoms like breathlessness, a persistent cough, and nasal congestion. Fatigue that is profound and does not improve with rest.
What makes MCAS particularly difficult to recognise is that symptoms are often episodic and variable. You might be relatively well for a few days and then suddenly floored by a reaction. Symptoms can shift and change over time. Some things that trigger you one day have no effect the next. And critically, most standard blood tests come back completely normal.
This combination of multi-system symptoms, variable presentation, and normal investigations is precisely why MCAS is so frequently missed, dismissed, or misdiagnosed as something else entirely.
Why is it so under-diagnosed?
There are several reasons, and none of them reflect well on how medicine has historically approached complex chronic illness.
First, MCAS was only formally defined in the peer reviewed literature in 2007 and the diagnostic criteria were not internationally agreed upon until 2010 and have been refined since. It is a genuinely new diagnosis in medical terms, which means that a significant proportion of practising doctors qualified before it was widely taught.
Second, the investigations used to diagnose MCAS are not part of routine NHS blood panels and many GPs are simply not aware that they exist or how to interpret them. A normal full blood count tells you nothing about mast cell activity.
Third, because symptoms affect so many different body systems, patients are often sent to multiple specialists who each see only one piece of the picture. The gastroenterologist investigates the gut. The cardiologist investigates the heart. The dermatologist investigates the skin. Nobody joins the dots. Nobody asks why all of these things are happening to the same person at the same time.
And fourth, the overlap with anxiety, chronic fatigue, irritable bowel syndrome, and other functional diagnoses means that patients are frequently told their symptoms are stress related and sent away without answers.
The good news
MCAS is treatable. Not just manageable but genuinely treatable, with structured treatment protocols that work for the majority of patients. Many of the patients I work with at Mend Clinic have spent years being told nothing was wrong before finally getting the right diagnosis and the right treatment. The transformation in their quality of life is remarkable.
That is what this series is about. Not just understanding what MCAS is, but understanding what it means for you and what you can do about it.
Part 2 I am going to take you through the conditions that most commonly overlap with MCAS, including POTS, hypermobile Ehlers-Danlos Syndrome, and Long Covid, and why treating these conditions in isolation rarely works. This is the piece that changes everything for most people.
I am very close to launching a low cost new service that allow people to actually see if there sympotms could be mcas, stay tuned for this.
Stay Well
