Is mast cell activation syndrome real? As a spoiler, yes, I truly believe MCAS is real. I'm not a doctor, so I can't give you facts and figures or the results of peer-reviewed studies, but I can tell you my story . . .

It was a sunny spring morning, noticeably brighter and warmer than the past few days. Yet I felt noticeably warmer in a rather strange way as I walked to work, coffee in hand. My face felt as though I had sunburn. In March. Which couldn't possibly be the case, and certainly not at 9am, could it?
That feeling of sunburn marked the day I started to experience the symptoms of mast cell activation syndrome (MCAS) and, in turn, become embroiled in the battle over whether mast cell activation syndrome is a real medical condition or not.
I am not a doctor or healthcare professional, and this post does not constitute medical advice. It is simply my story and experiences and for informational purposes only.
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Strange symptoms
On that walk to work I assumed I had a cold coming, or some sort of virus that would last a week, maybe two if I was unlucky. The weeks passed by, and it got worse. I had flushing on my face, and was turning pinker and pinker. It hurt so much. A burning stinging pain that felt relentless.
Then the night sweats began. I would sleep with the window open, even on cold nights, and with only a sheet rather than a duvet. Pyjamas were soon forgotten. Despite this I felt as though I was boiling hot, as though I was in a sauna with no relief.
Twice I woke in the middle of the night truly hot to the point I was shaking and feeling incredibly faint and dizzy. Something was going on, seriously wrong, so I went to A&E (the ER in the UK). They had no idea what was wrong, and put it down to a UTI I tested positive for. I went back and forth to the GP, begging for help, saying over and over that these symptoms were new, and worsening as the days passed.
And expensive appointments
Next up was spending an incredible amount of money on private medical appointments as I wasn't getting anywhere on the NHS. I went up several flights of the Shard to see a neurologist, and into the City to a rheumatologist. They put it down to existing conditions, of PoTS and fibromyalgia. But something in me knew that wasn't the case. Something had changed with my body. I just had to figure out what.
Then, at a routine NHS appointment (how ironic after all the money I spent!), MCAS was mentioned. I hadn't ever heard of it before. Which meant I didn't know that MCAS is a controversial diagnosis for some doctors, or think to ask the basic question 'is mast cell activation syndrome real?' to hear his answer. The doctor in front of me had no doubt that this may be an issue for me. I was advised to follow a low histamine diet and take prescribed antihistamines.
Hope can be found in a diagnosis. It affirms that what you are experiencing is very real, and very disabling. It brings the possibility of treatment, of feeling better to some degree.
So I skipped out of my appointment (in a sense!). I had a suggestion of what was wrong. Other patients will know how confusing that moment is. You don't want to have a medical diagnosis, but there is also such a sense of relief if it makes sense of your symptoms and potentially leads to treatment.
I was fortunate that several other of my doctors agreed that I could have MCAS. They suggested a specialist doctor, I had tests and they were positive. Medications were prescribed, and I stuck to the low histamine diet. It took a long time to see a benefit, but I stopped getting night sweats and my face became less painful. It's important to note that response to treatment is often part of the diagnostic approach to MCAS (Mast Cell Action).
Then came the denials . . .
But then the denials came. I was referred to a doctor with an 'interest' in mast cells to further investigate gut symptoms. Rather astonishingly, she spent the first 15 minutes of my appointment telling me how controversial MCAS was as a condition and that I probably didn't have it. She declined to review my tests, and talked about guidelines that I later learnt weren't relevant. In turn, I declined to see her again . . .
This pattern of being told that MCAS is a controversial diagnosis happens to this day. It isn't a one-off, and is usually said with a weary look and a shake of the head. I wonder though if those doctors have actually done any research on MCAS. Or maybe they just hear that it is controversial from others and so parrot that back to their patients?!
The difficulty of getting a diagnosis
Getting a diagnosis of MCAS is often a journey full of potholes and twists and turns that can take a very long time. People in MCAS forums describe that they repeatedly get rejected by doctors who claim MCAS doesn't exist, and I've had that experience a number of times. Notably, those doctors don't ever have any suggestion for what they think I do have to account for my symptoms (never mind my test results) if it isn't MCAS . . .
Because it's all in your head
Of course, the old trope of 'it's all in your head' gets invoked often. Usually along the lines of 'well, anxiety can cause some of those symptoms'. That problematic (and often gendered) assumption of symptoms that can't easily be identified stemming from anxiety often means people (women?) can't access a diagnosis.* Discussions in forums highlights that this includes people who have had repeated episodes of anaphylaxis.
At a therapy appointment many years ago, the therapist (who I promptly 'sacked') heavily implied that my symptoms were anxiety and not MCAS. Upon what she was basing her assertion is questionable given that she wasn't a medical doctor. She asked what I thought of 'syndrome' conditions or those where you can't see symptoms, and whether they are actually real. She looked annoyed, and then as if she didn't know quite what to say, when I pointed out that you can't 'see' other conditions such as IBS on a scan or a blood test, yet no doctor would deny that it exists.
*Of course, many people live with anxiety and it has similar symptoms to MCAS. I am in no way undermining the difficulty of living with anxiety. However, the issue for those with MCAS lies in doctors not considering other conditions aside from anxiety. Anecdotally, many people get told they have anxiety but go on, many years later, to receive a diagnosis for other conditions which would have benefitted from treatment.
Some figures
I can't find figures for the number of people who seek a MCAS diagnosis, and I imagine that data doesn't exist. It's actually thought that MCAS may be common in the general population (PoTS UK). Yet it is under-recognised by doctors and healthcare professionals.
However, I do want to point to a poll undertaken by the stuffthatworks_community on the question 'Was it hard to get diagnosed?'. For MCAS, the figure was 'yes' from 77% of contributors. It is awful that over three-quarters of people faced such a challenge.
Not mentioning MCAS
Anecdotally, one path to at least getting treatment for MCAS (even if not a diagnosis of the condition) is not to mention MCAS. Confused? Yes, I was to begin with too.
In the UK the NHS doesn't formally recognise MCAS. It doesn't have NICE guidelines and there isn't, to my knowledge, any such thing as an MCAS clinic. I've had immunologists tell me they have no specialist knowledge in the condition, and that there isn't provision for its treatment.
Some mast cell groups advise people who suspect they have the condition not to mention it to their doctor. Instead, it is suggested to speak of the symptoms and to especially mention any reactions to medications, food, heat, exercise or any other obvious triggers. Why? Because, as I had the experience of, if MCAS is mentioned on a referral letter, the referral will likely be declined. The objective is not to mention MCAS and hope that an appointment is given and that the doctor will provide treatment for the symptoms. It is a bizarre system, and a rather strange game having to be played by patients simply desperate for some answers, and some help.
Final thoughts
So is mast cell activation syndrome real? As I've already mentioned, I can't give a definitive medical answer to this. If it's a debated topic then a patient like me clearly can't say yes or no. I do know though, that I have significant symptoms, associated conditions, test results that show raised histamine levels and that my health has improved since being on treatments for the condition. No doctor has been able to give an alternative explanation for those symptoms.
What I can say is that I have noticed a shift over the past few years towards recognition and acceptance of the condition. I am no longer met with blank stares 90% of the time when I mention it to a new doctor. It's maybe only 30-40% of the time now. Health organisations are starting to crop up, either focused on the condition or mentioning it as associated with others.
Lately, the growing recognition of long covid and an association with MCAS has sparked new questions and debates. It appears that some long covid patients are now experiencing MCAS, or symptoms that mirror the condition. Research is clearly needed to investigate this further and assist those in need of treatment.
As a patient diagnosed with MCAS I can say that my diagnosis is important. It gives me access to treatment, first and foremost. That treatment has changed my life in a positive way. Am I free of symptoms? No, sadly not. But they are better than they were and so my life is better than it was. It is upsetting to think about how many people are out there suffering because they can't get a diagnosis or treatment.
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Katie. Clark says
Sure am glad you've found a good doctor to guide you. You have found relief from the changes you've made based on MCAS protocol. But, it sure can be difficult when it isn't fully accepted diagnosis and isn't well understood in the medical community.
throughthefibrofog says
It's so difficult and sadly means many of us having to pay for private appointments to see a specialist as there isn't provision on the NHS.
Sheryl Chan says
Thank you for sharing about your experience. I'm surprised that MCAS isn't recognised in the UK formally. That's so weird! It must be so frustrating not only to be undiagnosed, or take a long time to reach a diagnosis, but to have it claimed as 'not real'.