MCAS // Symptoms
The symptoms of MCAS are numerous, varied and seriously complex. They can come and go or be chronic, can fluctuate from day-to-day or even hour-to-hour and can affect any part of your body. MCAS affects multiple organ systems simultaneously and can often ‘mimic’ the symptoms of other conditions making it extremely difficult to diagnose.
Head
Inflamed hair follicles
Medical: folliculitis
Typically develops spontaneously with no identifiable cause.Fatigue
Very common. Most patients remain functional day-to-day but in some cases fatigue can be mildly to severely disabling.Hair loss
Medical: alopecia
Very common. May be linked to the mast-cell specific chemical mediator Prostaglandin D2 but more research is needed.Dry and Itchy eyes
Very common. Typically a dry, itchy, sandy, gritty sensation.Inflamed and watery eyes
CommonEyelid tics and tremors
Sometimes treated with botox injections but with limited success.Blurred vision
Typically lasting minutes to hours and may coincide with a number of other symptoms during a flare.Painful and/or itchy ears
UncommonMiddle ear infection
Common. May be a more common presentation in children and typically persists despite antibiotic treatment.Hearing loss
May be related to a condition called otosclerosis where a tiny bone in your ear called the stapes fuses with other parts of your ear.Ringing in the ears
Medical: tinnitusHeadache and/or Migraine
Increased sensitivity to sound
Medical: hyperacusisNasal congestion
CommonNasal inflammation
Nasal ulcers or sores
Typically intermittentIncreased sensitivity to smell
CommonNose bleeds
Medical: epistaxsis
Common. Typically intermittent and unpredictable.
Torso
+ arms & legs
Elevated temperature
Common. Typically intermittent. Most patients report ‘feeling hot’ but don’t have a fever.Chills
Uncommon. Typically intermittent shaking chills.Feeling cold
Common. A near-constant sense of feeling cold without necessarily suffering from intermittent chills.Unprovoked sweating
Medical: Diaphoresis
Common. Some patients may experience unprovoked sweating at regular times of the day in line with their circadian rhythm e.g. “night sweats”.Enlarged and/or tender lymph nodes
Typically where no known infectious cause can be found.Loss of appetite
Medical: anorexia
May be accompanied by feeling full very quickly when you do eat. This symptom is distinct from the fear of eating experienced by some MCAS patients following unexpected reactions to foods.Feeling sick
Medical: nauseaWeight loss
Many MCAS patients understandably become fearful of food due to unpredictable reactions which can lead to dietary restriction. This in turn may lead to weight loss in some cases.Weight gain
Common. Weight may increase rapidly without any identifiable changes in your diet or activity. Fluctuations in weight may be due to fluctuating water-retention (oedema).Poor wound healing
Typically taking a longer period of time to close than expected which may result in a secondary infection and pronounced scarring.Skin writing
Medical: dermatographism
A form of urticaria where lightly scratching the skin leaves a pronounced and persistent mark for several minutes.Itching
Medical: Pruritus
Common. Typically episodic and unpredictable but can be chronic and in some cases severe, life-altering and disabling. Can affect different parts of the body at different times. Sometimes triggered by hot showers or baths.Rash
Medical: Macular rash
Very common. Typically unpredictable, patchy and may move around your body.Flushing
CommonSwelling
Medical: Angioedema
Common. Typically episodic but can be chronic.Painful skin
Uncommon. Typically with no identifiable trigger, usually affecting an entire region of your body (e.g. an arm)Dry Skin
Sores / Ulceration
Common. Ranging from 1-2mm to 2-4cm in diameter and are typically slow to heal.Stretch marks
Medical: striae
Typically seen across the abdomen, lower back and around the armpits. These marks may disappear once MCAS is treated effectively.Frequent urination and/or incontinence
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There is, understandably, no definitive list of MCAS symptoms as the condition is so variable.
The symptoms listed on this page are by no means exhaustive but are based on the clinical observations and experiences of Dr Lawrence Afrin and his team. Dr Afrin is arguably a world expert in Mast Cell Activation Syndrome.
[1]
Afrin LB. Presentation, diagnosis, and management of mast cell activation syndrome. In: Murray DB, editor. Mast Cells: Phenotypic Features, Biological Functions and Role in Immunity. New York: Nova Science Publishers; 2013. p. 155–232.
HARD TO BELIEVE
The sheer number of symptoms attributed to Mast Cell Activation Syndrome seems ludicrous at first glance. A condition that causes hundreds of symptoms in disparate parts of the body, that comes and goes, seemingly at random, is pretty hard to wrap your head around.
The extreme number and variety of symptoms is arguably one of the cruelest aspects of MCAS as they seem so far-fetched, so outlandish, that many people are disbelieved. As a result, Munchausen Syndrome, a psychological condition where people pretend to be ill, is a common and extremely distressing misdiagnosis seen in MCAS patients. [1]
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[1]
Weinstock LB, Nelson RM, Blitshteyn S. Neuropsychiatric Manifestations of Mast Cell Activation Syndrome and Response to Mast-Cell-Directed Treatment: A Case Series. J Pers Med. 2023 Oct 31;13(11):1562. doi: 10.3390/jpm13111562. PMID: 38003876; PMCID: PMC10672129.
WHY SO MANY SYMPTOMS?
In order to answer this question there are a few things you need to know about mast cells in general…
First, Mast Cells are an ancient type of immune cell linked to numerous functions in your body including blood vessel regulation, injury healing, bone growth regulation, gut flora regulation and they can even communicate directly with your nervous system [1]. These are definitely multi-skilled cells.
Second, mast cells can produce anywhere from 200 to over 1000 chemical mediators which not only act at the site of an injury or pathogen, sometimes producing dramatic effects like swelling or anaphylaxis, but can also affect cells and tissues in distant parts of the body simultaneously. Their effects are far-reaching.
Third, mast cells are located in every organ system in your body, from your head to your toes. While they typically take up residence in your tissues like sentinel soldiers keeping guard, they can also move around your body to where they’re needed. They’re everywhere.
So, with this in mind, if your mast cells were to malfunction the effects would not only be diverse but could potentially affect multiple parts of your body.
The KIT Gene plays a crucial role in determining how mast cells function and for many years it was believed that one specific mutation (D816V) in this gene was responsible for most cases of mast cell disease. However, this genetic mutation isn’t always found in those with MCAS.
Then, in 2007 it was discovered that many mast cell disease patients, including those with MCAS had not one, but multiple mutations across the KIT gene [2] and multiple mutations mean multiple errors in the way mast cells behave.
This area of medicine is incredibly complex and remains the focus of ongoing research. However, the discovery of multiple genetic mutations may help explain the vast variability and numerous symptoms associated with MCAS.
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[1]
Wong C. What Are Mast Cells? Verywell Health. 2023 Nov 10 [cited 2026 Mar 11]. Available from: https://www.verywellhealth.com/what-are-mast-cells-1944889[2]
Molderings GJ, Kolck UW, Scheurlen C, Brüss M, Homann J, Von Kügelgen I. Multiple novel alterations in Kit tyrosine kinase in patients with gastrointestinally pronounced systemic mast cell activation disorder. Scand. J. Gastroenterol. 2007; 42:1045-53.
HOW BAD CAN SYMPTOMS GET?
The severity of symptoms, like everything else about MCAS, varies wildly. Most people navigate a broad spectrum, ranging from mildly annoying rashes and headaches to persistent muscle aches, fatigue, and nausea that can be incredibly tricky to manage.
There is, however, a distinct subset of people at the extreme end of this spectrum. For them, symptoms aren't just difficult to control; they’re severe and potentially life-threatening. At its worst, MCAS can induce something called Non-Immunological Anaphylaxis, where your mast cells essentially flood your body with more inflammatory mediators than it can handle. This 'mast cell storm' triggers a classic anaphylactic emergency — confusion, racing heart, swelling of the lips and throat, and difficulty breathing.
While technically different from a standard allergic reaction, the impact is identical, just as serious, and requires immediate medical intervention.
I will stress once again though, that this extreme manifestation of MCAS doesn’t affect everyone but does highlight why the condition should always be taken seriously.
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