Do You Have Unpredictable Allergies? Blame Mast Cells

Nurse Amy Lochtie was in a meeting about infection control the first time she went into anaphylaxis — a severe reaction, usually related to an allergy, which can be life-threatening. But in her case, despite working in a hospital, no one could work out what had triggered it.

After three anaphylactic reactions in the space of a week, Amy, 34, was admitted to hospital where she spent two weeks being treated with a combination of nebulizers, steroids and antihistamines, before being discharged and referred to the allergy centre. But with no apparent cause for these life-threatening attacks, this referral proved less than helpful. “No one really understood what was going on, and the allergy centre was horrendous, just awful,” Amy says. “One registrar said I was just having a panic attack and it was all in my head. It was like, there’s no reason for this to be happening, so you’re obviously lying.”

It wasn’t until two years later, when Amy had a very rare anaphylactic shock to her flu jab which, as a nurse, she had previously had every year without issues, that she finally started to get some answers. Because of this, doctors were more cautious about giving her the COVID vaccine: “I thought I was never going to be able to leave my house again,” she recalls.

In desperation, Amy — who lives in the UK — contacted her local MP on Twitter, who put her in contact with an immunologist. “[The immunologist] was amazing. He was like, ‘this is ridiculous, come in and we’ll sort it out’. He not only managed to safely give me my COVID vaccine, but also took me into his care and got me a diagnosis to explain why I was living like this,” she says.

Amy was diagnosed with Mast Cell Activation Syndrome (MCAS), a little-known condition that can cause inflammatory reactions anywhere in the body because of an overactive immune response.

Mast cells are a type of white blood cell found throughout the body, which play a key role in our immune defences. When they’re working normally, mast cells react to threats like bacteria, parasites, viruses, stings and wounds, releasing chemicals (mast cell mediators) to help fight infection and promote healing, as well as signaling to other cells.

In someone with MCAS, however, the mast cells are activated too much, or in response to triggers that aren’t normally considered harmful, like fragrances, exercise, stress, vibration or changes in temperature. Even once healing has occurred, the overactive mast cells don’t return to their normal resting state. Instead, they may continue to release their many chemicals unnecessarily, keeping the immune system in a constant (and exhausting) state of high alert. 

MCAS was only discovered relatively recently; the name was first used in 2007 and proposed criteria for the condition were published in 2013 — although there still isn’t a proper consensus within the medical community about who should be labeled as having it, explains Dr Emma Reinhold, a former GP, researcher and clinical advisor on MCAS. 

As a result, data on MCAS remains very limited. What little research we do have suggests it disproportionately affects women and people assigned female at birth (AFAB), who outnumber men with MCAS three to one. Perhaps unsurprisingly though, medical science can’t yet explain the disparity. 

“Nearly all of my patients are women, but I’m not sure there’s really much understanding about why that is,” says consultant haematologist Dr Bethan Myers, who works at the University of Leicester NHS Trust. “There is some hormonal link, with mast cells having oestrogen and progesterone receptors, but I don’t think it’s been looked into in much detail.” 

Complicating the matter is the fact that the symptoms of MCAS (fatigue, low-grade fevers, and feeling generally under the weather) can feel like you have a cold or flu. Even more confusingly, mast cell hyperactivity can also lead to a wide range of seemingly unrelated symptoms throughout the entire body — from your breathing, your gut, and your brain, to more common allergy-like symptoms, such as nasal congestion and watery eyes, and skin reactions like hives, swelling and itchiness. Frustratingly, they can develop at any time and change over time.

Sophia, who chose not to share her last name, has had a laundry list of symptoms since she was diagnosed with MCAS at the age of 22 three years ago. “It’s mostly reacting to different foods, coming out in rashes and hives, or really bad general allergy symptoms, like hay fever times ten. I also have very difficult asthma, so those reactions affect my chest and I’ve had many intensive care admissions as a result."

Sophia also has to avoid a growing list of ingredients, including dairy, soya, and more recently rice flour, which is used in a lot of the ‘free-from' food she used to eat as it is “low in histamines”. “My MCAS is ever-evolving,” she adds, “sometimes I’ll just react to things really badly and I don’t know why.”

It’s this unpredictability that differentiates MCAS from standard allergies. “Allergies involve an adaptive immune response to a specific (protein) allergen; a response which has been ‘learned’ by previous exposure and is absolutely predictable. For example, every time someone with a peanut allergy is exposed to peanuts, they will react within seconds or minutes,” Dr Reinhold explains. “MCAS involves the innate, more primitive side of the immune system, whereby multiple factors – including hormones, stress levels, other triggers you’ve been exposed to that day – determine the mast cells’ reaction”.

The complexity and multi system (whole body) nature of MCAS also makes it tricky to diagnose. Of course, this isn’t helped by huge gaps in research and data on MCAS, difficulties in testing for it, and the fact that many doctors aren’t even aware of the condition yet. This may in part be down to its relatively recent discovery, but it’s hard not to wonder if the fact it predominantly affects women — who, like Amy, may find themselves dismissed as ‘hysterical’ or making it up — also plays a part.

Another common link is long COVID, with some COVID ‘long haulers’ reporting MCAS symptoms triggered by the virus among their symptoms. Again, research is limited, but one small study found a “high prevalence” of MCAS symptoms among long COVID patients. This, Dr Myers says, has at least helped to highlight the condition within the medical community, which she hopes will lead to more research being done.

In the meantime, the treatment options, which range from antihistamines to more intensive corticosteroids, it’s largely a case of symptom management, says Dr Myers.

“Perhaps in the future we will understand more and be better able to predict which medications are likely to help the most. For the time being, management often involves some trial and error to find a solution that works for each individual patient,” Dr Reinhold adds.

Amy — who now works in a non-clinical role for the NHS — has tried various options, and currently has injections every four weeks, which help to block mast cell activation. Really though, she says, MCAS is just something she’s had to learn to live with.

“I have a busy job, I have a three-year-old, so it’s really inconvenient for me when a flare does happen; I don’t have time to be unwell. But when you’re having a flare, at least people can obviously see you’re ill if you’re swelling up or covered in hives,” she says.

“I think what people don’t realize, underlying that, is how your body’s constantly attacking itself all the time and you’re exhausted. No one can see that part, and you just have to crack on. I like to think my superpower is that my body regularly tries to kill me, and I don’t die.”