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:
Allergic responses
Inflammation
Gut function
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:
Abdominal pain
Diarrhoea or constipation
Bloating
Nausea
Food intolerance
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
Abdominal pain
Diarrhoea or alternating bowel habits
Bloating
Nausea
Acid reflux-like symptoms
Skin symptoms
Flushing
Itching
Hives
Rashes
Cardiovascular and neurological symptoms
Palpitations
Dizziness
Brain fog
Fatigue
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:
Genetic predisposition
Chronic inflammation
Autoimmune conditions
Infections
Gut dysbiosis
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:
Typical symptom patterns affecting multiple systems
Laboratory markers, such as tryptase or urinary histamine metabolites
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
Antihistamines (H1 and H2 blockers)
Mast cell stabilisers
Low-histamine or personalised diets
Addressing gut inflammation and dysbiosis
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:
IBS
Functional dyspepsia
Reflux symptoms
Chronic fatigue
Autonomic dysfunction
A specialist approach helps avoid misdiagnosis, unnecessary treatments, and prolonged symptoms.
Book a Specialist Assessment
Persistent unexplained symptoms affecting multiple systems?
If your digestive symptoms coexist with flushing, fatigue, or food reactions, mast cell activation syndrome may be contributing.