- What is Mast Cell Activation Syndrome? - 12 May 2025
- Breakthrough For Ehlers Danlos Syndrome and Endometriosis - 13 March 2025
- Does EDS get worse as you age? - 20 February 2025
Let’s talk about mast cells, because frankly, it’s something that doesn’t get spoken about, when it really should be. If you’ve never heard of them before, that’s completely understandable, as these immune cells don’t get much airtime in most conversations, but when they start misbehaving, the effects can be profound and in some cases, absolutely devastating.
Mast Cell Activation Syndrome, often shortened to MCAS, is one of those more complex conditions that can leave people feeling frustrated and dismissed, because when It does occur, mast cells become overactive, releasing too many chemical substances like histamine, prostaglandins, and leukotrienes. The problem is that these substances are meant to help you during an allergic response, but with MCAS, they’re being released at the wrong time, in the wrong amounts, and for no good reason: obviously causing major issues.
Because of how mast cells work, they can trigger symptoms in virtually any part of the body, meaning some people experience hives, itching, or unexplained flushing, where as others feel it in their gut with cramping, nausea, or diarrhoea. For many, the symptoms shift and change, which only adds to the confusion. You might feel wired one minute and exhausted the next, or suddenly find yourself reacting to foods and smells that never used to bother you.
What makes MCAS even more difficult to spot is the wide range of potential triggers, including things like stress, exercise, temperature changes, food, medication, or even seemingly benign environmental exposures. Be cause MCAS is extreeamly preelant in conditions such as hypermobility and EDS, it makes exercsing with hypermobility very difficult, which in of its self is a problem, because this population needs exercise to help stabilise loose joint.
There’s often no clear pattern with MCAS, and symptoms can flare up unpredictably, which makes people question their own experiences.
Diagnosing MCAS is rarely simple. There is no one test that can confirm it. Instead, diagnosis usually involves observing symptoms across multiple systems, combined with blood and urine tests to detect elevated levels of mast cell mediators. A skin or tissue biopsy may also be considered to look for signs of abnormal mast cell activity. But even with all this, many people spend years searching for answers.
The good news is that once MCAS is recognised, there are ways to manage it. Treatment usually involves antihistamines, mast cell stabilisers, and other medications aimed at calming the overreaction. Avoiding triggers and making certain lifestyle changes can also be incredibly helpful.
If any of this sounds familiar to you, know that you are not alone. MCAS might not be a household name, but more and more people are finding clarity and support after years of mystery symptoms. There is hope, and there is help.
How Common is MCAS?
When I first came across MCAS, I was told it was rare, and that was my prevailing thought for a long time. But once I started working with clients who had complex, multi-system symptoms, it quickly became clear that this was not as rare as many believed. Similar to how we used to believe EDS was very rare.
Current estimates suggest that anywhere from 10 to 17 percent of the population might be affected by MCAS. That number is much higher than most people would expect. It is likely even more prevalent in those with conditions like Ehlers-Danlos Syndrome, POTS, and other forms of dysautonomia. While those numbers are not set in stone, they give us a strong hint that MCAS might be far more common than we realise.
One of the challenges with getting an accurate number is how variable the symptoms can be. Because MCAS often overlaps with other chronic conditions, it is sometimes mistaken for something else. And because many of the symptoms are invisible or hard to quantify, it can be dismissed entirely.
We still need a lot more research to fully understand the scope and impact of MCAS. But what is already clear is that it often goes unrecognised for years, even in people who are seeing multiple specialists.
If you live with chronic illness and have a combination of allergic-type symptoms, digestive issues, or neurological complaints that don’t seem to fit into a neat box, it’s worth considering whether MCAS could be playing a role.
The path to diagnosis may not be easy, but understanding what’s happening in your body is the first step towards reclaiming your health and quality of life.
Diagnosing Mast Cell Activation Syndrome
If you’ve been chasing symptoms for years without answers, you’re not alone. MCAS has a reputation for being incredibly difficult to diagnose, and with good reason. Its symptoms can affect almost every system in the body, they can change from day to day, and they often mimic other conditions. It’s no surprise that many people go through years of testing before they finally land on the right diagnosis.
The first clue is usually a pattern of symptoms involving multiple body systems. For example, someone might have digestive issues like cramping or nausea, but also struggle with flushing, fatigue, and brain fog. When two or more systems are affected during the same flare-up, it raises the possibility that something bigger is going on. That’s often where MCAS starts to come into the picture.
One early step in the diagnostic process is seeing how symptoms respond to treatment. If someone begins taking antihistamines or mast cell stabilisers and sees a clear improvement, this can strongly support the diagnosis, even before any test results are back. It’s not proof on its own, but it’s a meaningful clue.
Testing for MCAS involves looking for elevated levels of certain chemical mediators. These are substances like histamine or prostaglandins, which are released when mast cells activate. Blood or urine samples are usually taken during a symptom flare, since that’s when these mediators are most likely to be elevated. But it is not just about one test. In some cases, 24 hour urine collections or even tissue biopsies are needed to build the full picture.
It’s also important to know that many people with MCAS have normal baseline tryptase levels. This can lead some doctors to wrongly rule it out early on. Tryptase is more helpful for detecting mastocytosis, another mast cell disorder, but not always reliable in MCAS.
Unfortunately, there are no genetic tests available yet for diagnosing MCAS. Research is ongoing, and hopefully that will change in the future. For now, diagnosis is largely clinical, based on symptoms, history, and how the body responds to treatment.
Another crucial part of the process is ruling out other conditions. Many of the symptoms of MCAS overlap with other illnesses like eosinophilic disorders, Addison’s disease, certain cancers, epilepsy, and autoimmune conditions. It’s essential to rule out these other possibilities so that no critical diagnosis is missed. In some cases, additional testing like endoscopies, imaging, or biopsies may be required.
If you suspect MCAS and are struggling to get answers, it’s vital to work with someone who understands the condition well. A specialist with experience in complex multi-system illnesses can help guide you through the process, avoiding dead ends and making sure you’re not left feeling dismissed or misunderstood.
Getting a diagnosis can be a long road, but clarity is the first step towards finding the right treatment and starting to feel better.
Comorbidities of Mast Cell Activation Syndrome
One of the most important things to understand about MCAS is that it rarely travels alone. It is often found in people who also have other chronic conditions, especially those involving the immune or nervous systems.
If you have MCAS, there’s a strong chance you may also be dealing with Ehlers-Danlos Syndrome, POTS, or other forms of dysautonomia. These are some of the most common comorbidities we see, and they often exist in a kind of feedback loop. For example, POTS can trigger mast cell activation, and mast cell flares can worsen POTS symptoms. It can be difficult to untangle where one condition ends and the other begins.
Beyond those, there is a long list of other conditions that are frequently seen alongside MCAS. These include hypermobility spectrum disorders, fibromyalgia, irritable bowel syndrome, migraine, asthma, and chronic fatigue syndrome. You may also see autoimmune or inflammatory conditions such as rheumatoid arthritis, lupus, and multiple sclerosis in this mix. Even conditions like Type 2 diabetes and COPD have been linked to mast cell issues in some people.
We still don’t fully understand why MCAS is connected to so many other health problems. It may be that an underlying issue with connective tissue or immune regulation creates a kind of shared vulnerability. Or it could be that mast cell overactivation makes other existing conditions harder to manage.
Either way, this overlap is important. It means that treatment for MCAS should never happen in isolation. A good management plan looks at the whole person, not just one part of the picture. That’s why it’s so important to work with someone who understands how these conditions interact.
If you’ve felt like your body has been in chaos and nothing quite fits, this might help connect some of the dots. Understanding your comorbidities can help you build a more complete picture of your health and start to find more targeted, effective ways to support it.
What Causes Mast Cell Activation Syndrome?
If you’re looking for a simple explanation about what causes MCAS, you might be in for a bit of frustration. At this point in time, the exact cause of MCAS remains unclear. That’s not to say we don’t have some promising leads, but as with many complex conditions, the science is still catching up to what patients have known for years, that something very real is happening, even when the cause isn’t obvious.
There are three main types of MCAS currently recognised, and each one has a slightly different origin story. The first is called primary MCAS. This occurs when there’s a specific mutation, usually the KIT D816V mutation, and the mast cells express certain markers like CD25. In some cases, this overlaps with another condition called mastocytosis, where the body produces too many mast cells rather than just activating them excessively.
The second type is known as secondary MCAS. This is where mast cell activation is triggered by another condition, often an allergic response. Things like food allergies, environmental triggers, or autoimmune responses can all play a role here. In this case, the mast cells are reacting to something real, but they’re doing it in a way that causes harm instead of helping.
Then there’s idiopathic MCAS. This is the most frustrating of the three, because it simply means we don’t yet know why it’s happening. There’s no mutation, no clear allergic cause, and nothing obvious showing up on tests. It’s a diagnosis that requires ruling everything else out, which can be a long and exhausting journey for the person going through it.
Some researchers are exploring the idea that there may be a genetic component involved. It’s also possible that long-term stress, trauma, or environmental exposures play a role in dysregulating the immune system and pushing mast cells into a hypersensitive state.
Although the cause may not be clear, what matters most is that the symptoms are real, and people deserve to be believed and supported as they search for answers.
Symptoms of Mast Cell Activation Syndrome
One of the most overwhelming things about MCAS is just how many symptoms it can cause. Because mast cells are spread throughout your entire body, the effects of their activation can be incredibly widespread.
Let’s start with the skin, because that’s often where people first notice something is wrong. You might experience itching, flushing, hives, or even swelling. These symptoms may come and go without warning, or they might flare in response to things like heat, stress, or certain foods.
Eyes and nose can be affected too, with watery eyes, nasal congestion, or a persistent runny nose that seems like allergies but doesn’t quite respond to antihistamines the way it should.
The mouth and throat may also be involved, with sensations of swelling or tightness, particularly in the tongue or lips. In some cases, people report feeling like their throat is closing, even though there’s no obvious obstruction.
Then there’s the lungs. Mast cell flares can trigger wheezing, coughing, or a sense of breathlessness that mimics asthma but doesn’t always respond to standard asthma medications.
The cardiovascular system is another area frequently hit by MCAS. Symptoms can include a rapid heart rate, lightheadedness, or even a sudden drop in blood pressure. In more severe cases, this can escalate into anaphylaxis, which is a life-threatening emergency and requires immediate treatment with epinephrine.
The gut is a very common site of mast cell involvement. People often report cramping, nausea, bloating, diarrhoea, or abdominal pain. These symptoms are easily mistaken for IBS or food intolerances, which is why so many people are misdiagnosed for years.
Finally, the nervous system can be affected too. Headaches, brain fog, fatigue, and even a sense of confusion or detachment are common complaints. It’s like your brain is constantly trying to work through static.
These symptoms may appear one at a time or all at once. They might come and go, or they might stick around persistently. The pattern is rarely predictable, which can make life with MCAS feel very uncertain.
In severe cases, a person may experience full-blown anaphylaxis. This includes a rapid drop in blood pressure, difficulty breathing, and loss of consciousness. If that ever happens, it is vital to seek emergency medical care immediately.
You might be reading this and ticking off multiple symptoms you’ve been living with for years. If so, you’re not imagining it. This is real, and there are paths forward.
MCAS vs Mastocytosis
It’s really common for people to confuse MCAS with another mast cell disorder called mastocytosis. And honestly, it makes sense. Both conditions involve mast cells behaving in a way they shouldn’t, and the symptoms can look incredibly similar. But when we dig a little deeper, there are some key differences worth knowing.
Let’s start with mastocytosis. In this condition, your body produces too many mast cells. These extra cells often gather in the skin, bone marrow, or internal organs, and they can be easily triggered to release their chemical mediators. It’s not just that the cells are overactive—the problem starts with having too many of them in the first place.
Mastocytosis can be further broken down into cutaneous and systemic types. Cutaneous mastocytosis mostly affects the skin and often appears in childhood. Systemic mastocytosis is more serious and affects multiple organs. It can cause issues like liver or spleen enlargement, and in rare cases, may progress to a form of blood cancer known as mast cell leukaemia.
On the other hand, MCAS doesn’t involve an overproduction of mast cells. Instead, it’s the activation of normal amounts of mast cells that causes the problem. The mast cells are there in normal numbers, but they’re far too sensitive and prone to releasing their mediators without any real threat.
Another major difference is how we diagnose the two. With mastocytosis, doctors can often identify a specific mutation, such as the KIT D816V mutation, and they’ll usually see elevated tryptase levels in the blood. A bone marrow biopsy or skin biopsy often reveals clusters of mast cells, which helps confirm the diagnosis.
With MCAS, tryptase levels are often completely normal, and there’s no visible increase in mast cell numbers. Diagnosis relies more on tracking symptom patterns, ruling out other causes, and identifying elevated mediator levels during a flare.
While the two conditions share many symptoms, such as flushing, itching, and even episodes of anaphylaxis, the underlying mechanisms are different. That means treatment and long term management can differ as well.
If you’re exploring a possible diagnosis, make sure your healthcare provider understands both conditions. It’s important that you’re not misdiagnosed based on surface level similarities, because what works for one may not be helpful for the other.
Treatment Options for MCAS
There’s no single magic pill for MCAS, and currently, there is no cure. But that doesn’t mean you’re powerless. Far from it. Once you have a clearer understanding of your symptoms and triggers, you can begin to build a plan that helps reduce flares, manage reactions, and improve your quality of life.
The first place many people start is with antihistamines. These are often divided into two groups: H1 blockers and H2 blockers. H1 blockers like cetirizine and loratadine can help with skin-related symptoms like itching and rashes. H2 blockers like famotidine or ranitidine are more geared toward gut issues, including nausea or abdominal pain. Many people benefit from using both types together, depending on their symptom profile.
Another helpful category is mast cell stabilisers, such as cromolyn sodium or ketotifen. These help prevent mast cells from releasing their mediators in the first place. In some cases, people also respond well to omalizumab, a biologic medication that works by reducing the sensitivity of mast cells to triggers.
Then we have leukotriene inhibitors, like montelukast or zafirlukast. These target another type of mediator, often involved in breathing issues or gastrointestinal symptoms. If you’re dealing with wheezing, coughing, or cramping, these may offer some relief.
Aspirin is sometimes used to reduce flushing, but it should be approached with caution, especially if you have aspirin sensitivity or asthma. This is definitely something to discuss with a knowledgeable provider.
In more severe cases, corticosteroids may be prescribed. These are powerful anti-inflammatory medications, but they are usually reserved for short-term use during acute flares. Long-term use can cause significant side effects, so they are generally considered a last resort.
Perhaps one of the most important tools in the toolkit is epinephrine, especially if you’re at risk of anaphylaxis. If you have had episodes involving throat swelling, a sudden drop in blood pressure, or trouble breathing, carrying an epinephrine auto injector can be life saving. If you ever have to use it, emergency medical care is always required afterward.
It’s also a good idea to wear a medical ID bracelet, particularly if you have unpredictable or severe reactions. This helps ensure that first responders have critical information if you are unable to speak for yourself.
Managing MCAS is not just about medications. It’s also about identifying and reducing exposure to known triggers. This might include changes to your environment, stress management, or dietary adjustments. We’ll look at that more closely in the next section.
For now, know this: it may take time to find the right combination of medications and strategies, but many people do see significant improvement once they have a treatment plan in place. You deserve care that is tailored, evidence-informed, and compassionate.
Diet and lifestyle with MCAS
How small changes can make a big difference
If you’ve spent any time looking for answers about MCAS, you’ve probably come across a long list of dietary suggestions. And like so many aspects of chronic illness, the advice can feel overwhelming and often conflicting.
The reality is that diet does seem to influence symptoms for many people with MCAS, but the scientific evidence is still catching up. At the moment, we do not have large, conclusive studies confirming specific diets for MCAS. That said, many people report feeling better when they make certain changes, particularly when it comes to foods that are high in histamine.
The most common approach people try is a low histamine diet. This means avoiding foods known to contain high levels of histamine or that are thought to encourage mast cells to release more of it. These foods often include aged cheeses, smoked meats, alcohol, fermented products, and certain vegetables like spinach and tomatoes. While the evidence supporting these restrictions is still limited, many individuals notice a clear improvement in symptoms when they reduce these foods.
Another diet that sometimes helps is the low FODMAP diet. Originally designed for people with irritable bowel syndrome, this approach removes specific types of sugars that can ferment in the gut and cause digestive distress. Interestingly, one small study showed that a low FODMAP diet reduced histamine levels in people with IBS, which may explain why some people with MCAS also feel better following it.
Before making any significant changes, it is always worth speaking to a dietitian or a practitioner who understands both MCAS and nutritional balance. While restrictive diets can help short term, they can also lead to nutrient deficiencies if not managed carefully. The goal is not to eliminate every possible trigger, but to find a way of eating that supports your body and fits your life.
Beyond diet, lifestyle changes can also be powerful. Stress is a common trigger for mast cell flares, so calming the nervous system is often a key part of managing symptoms. Gentle routines like regular rest, deep breathing, or quiet walks can make a noticeable difference. Pacing your activities and creating space for recovery is not a luxury. For many, it is a necessity.
Avoiding common environmental triggers like strong perfumes or harsh cleaning products may also help. Using air filters, choosing low-chemical personal care items, and staying cool during hot weather are all things that might support your system and reduce daily flares.
The important thing to remember is that you do not need to get everything perfect. Start small. Focus on what makes a difference for your body. This is a journey of figuring out what works for you, not chasing a strict set of rules.
Living with MCAS: what’s the outlook?
There is hope, even when things feel uncertain
Being diagnosed with MCAS can feel like both a relief and a shock. On one hand, it finally puts a name to the strange and unpredictable symptoms you may have lived with for years. On the other hand, it raises a whole new set of questions about what comes next.
There is currently no cure for MCAS, but that does not mean there is no way forward. Many people living with MCAS see significant improvements in their symptoms once they understand their triggers and find the right combination of treatment strategies. This can include medications like antihistamines or mast cell stabilisers, changes to diet, stress management, and creating safer environments.
The road to feeling better is rarely fast or straight. Some people find relief quickly, while others take longer to find what works. The important thing is that progress is possible. Each small improvement, whether it is fewer flares or better sleep, builds a foundation for better days ahead.
Your personal outlook will also depend on whether you live with other conditions alongside MCAS. Conditions like Ehlers-Danlos syndrome, POTS, or autoimmune issues can add complexity to your health, but they can also be managed with the right support. When care is joined up and considers all aspects of your health, it becomes easier to see what is helping and where adjustments are needed.
It is easy to feel isolated when dealing with something as complex as MCAS. But the truth is, you are not alone. More people are beginning to recognise and understand this condition. There are communities, professionals, and resources out there that can help you navigate the path ahead.
Living with MCAS is not about eliminating every symptom or controlling every moment. It is about learning how to create a sense of safety in your body, even on the hard days. It is about finding rhythms that support you, building a team that listens, and making peace with the pace of your own healing.
You are not weak for struggling. You are not broken because your body works differently. And you do not have to walk this road without support.
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