A Patient’s Story
Sarah, 36, had years of unexplained symptoms. Flushing after meals. Abdominal pain one day, diarrhoea the next. Episodes of palpitations, brain fog, and fatigue that never fit into one diagnosis.
Tests kept coming back “normal”. Eventually, a specialist recognised the pattern. Sarah was diagnosed with mast cell activation syndrome.
What Is Mast Cell Activation Syndrome?
Mast cell activation syndrome (MCAS) is a condition in which mast cells release inflammatory chemicals inappropriately and excessively, without a clear allergic trigger.
Mast cells are immune cells involved in:
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Allergic responses
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Inflammation
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Gut function
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Nervous system signalling
In MCAS, these cells become over-reactive, releasing substances such as histamine, tryptase, prostaglandins, and cytokines, leading to multi-system symptoms.
Why Mast Cells Matter in the Gut
The gastrointestinal tract contains a high concentration of mast cells, making digestive symptoms particularly common.
Excess mast cell activation can lead to:
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Abdominal pain
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Diarrhoea or constipation
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Bloating
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Nausea
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Food intolerance
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Symptoms overlapping with IBS
This is why MCAS is increasingly recognised in patients with functional gut disorders.
Common Symptoms of MCAS
Symptoms often fluctuate and affect multiple systems.
Digestive symptoms
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Abdominal pain
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Diarrhoea or alternating bowel habits
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Bloating
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Nausea
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Acid reflux-like symptoms
Skin symptoms
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Flushing
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Itching
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Hives
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Rashes
Cardiovascular and neurological symptoms
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Palpitations
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Dizziness
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Brain fog
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Fatigue
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Headaches
Symptoms may worsen with food, stress, heat, exercise, infections, or hormonal changes.
What Causes Mast Cell Activation Syndrome?
The exact cause is not always clear. Triggers and associations include:
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Genetic predisposition
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Chronic inflammation
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Autoimmune conditions
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Infections
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Gut dysbiosis
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Stress and nervous system dysregulation
Unlike classic allergies, MCAS does not require IgE-mediated reactions.
How Is MCAS Diagnosed?
Diagnosis is clinical and requires specialist assessment.
It is based on:
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Typical symptom patterns affecting multiple systems
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Laboratory markers, such as tryptase or urinary histamine metabolites
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Response to mast cell–targeted treatment
Many routine tests appear normal, which is why MCAS is often missed or delayed.
Treatment and Management
There is no single cure, but symptoms can be effectively controlled.
Treatment may include
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Antihistamines (H1 and H2 blockers)
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Mast cell stabilisers
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Low-histamine or personalised diets
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Addressing gut inflammation and dysbiosis
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Nervous system regulation and stress management
Management focuses on reducing triggers, calming mast cell activity, and treating associated gut disorders.
Why Specialist Care Is Essential
MCAS is complex and overlaps with:
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IBS
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Functional dyspepsia
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Reflux symptoms
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Chronic fatigue
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Autonomic dysfunction
A specialist approach helps avoid misdiagnosis, unnecessary treatments, and prolonged symptoms.