Mast Cell Activation Syndrome (MCAS): Symptoms, Causes, and Treatment

Mast Cell Activation Syndrome (MCAS) involves overactive mast cells releasing excessive chemical mediators, causing allergic-type reactions affecting multiple body systems. Symptoms include skin reactions (hives, flushing), gastrointestinal issues, cardiovascular symptoms, and respiratory problems. Diagnosis requires meeting specific criteria, and treatment focuses on symptom management through medications and lifestyle adjustments. If you experience recurrent symptoms affecting multiple systems, consult a healthcare provider for proper evaluation.

In plain words

Mast Cell Activation Syndrome (MCAS) is when certain cells in your body (called mast cells) release too many chemicals. This can cause allergic-like reactions in different parts of your body. Symptoms might include skin rashes, stomach problems, trouble breathing, or feeling dizzy. These reactions can come and go and vary in how bad they are. MCAS is different from having too many mast cells (that's called mastocytosis). Doctors aren't sure exactly what causes MCAS, but it might be related to genes or problems with the immune system. There's no cure, but treatments can help manage symptoms. If you keep having these kinds of reactions, talk to a doctor.

What is Mast Cell Activation Syndrome (MCAS): Symptoms, Causes, and Treatment?

Symptoms

Early symptoms

Skin reactions: Flushing, hives, or itching without a rash are common early signs of MCAS. These symptoms often occur episodically and may be triggered by environmental factors like heat or fragrances. (2) (4)
Gastrointestinal issues: Nausea, abdominal pain, diarrhea, or bloating can occur due to mast cell activation in the digestive tract. These symptoms often fluctuate and may be mistaken for food intolerances. (2) (7)
Cardiovascular symptoms: Low blood pressure, rapid heart rate, or lightheadedness are common. These symptoms may occur during mast cell activation episodes and can mimic other conditions like anxiety. (2) (4)
Respiratory problems: Wheezing, shortness of breath, or nasal congestion may occur without a clear allergic trigger. These symptoms can be episodic and vary in severity. (2) (7)
Neurological symptoms: Brain fog, headaches, or fatigue are often reported as early warnings of MCAS. These symptoms can be non-specific and vary widely between individuals. (4) (7)

Serious or emergency symptoms

Anaphylaxis: Severe, life-threatening allergic reactions involving multiple systems. Symptoms include difficulty breathing, swelling of the throat, and a sharp drop in blood pressure. Use an epinephrine auto-injector (if prescribed) and seek emergency care immediately. (2) (7)
Severe cardiovascular collapse: A dangerous drop in blood pressure leading to shock. This can occur during severe mast cell activation episodes and requires urgent medical attention. Call emergency services immediately and administer epinephrine if available. (2) (7)

Causes

Primary causes

Genetic mutations: MCAS often involves genetic mutations affecting mast cell behavior, particularly in the KIT growth factor receptor pathway. These mutations can lead to abnormal mast cell activation. (1)
Immune dysregulation: MCAS is thought to be related to immune system dysfunction where mast cells release mediators inappropriately, even without IgE antibodies. (1)

Risk factors

Family history

Having a family history of mast cell disorders or autoimmune conditions may increase the risk of developing MCAS. (4)

Co-occurring conditions

Individuals with conditions like Ehlers-Danlos Syndrome or Postural Orthostatic Tachycardia Syndrome (POTS) have a higher risk of MCAS. (4)

Diagnosis

Diagnosis requires meeting strict criteria: 1) Recurrent, severe symptoms affecting ≥2 organ systems, 2) Lab evidence of mast cell mediator release during symptoms (e.g., elevated tryptase), and 3) Response to mast cell-stabilizing medications. Tests may include a 24-hour urine test for mast cell mediators and skin biopsy to rule out mastocytosis. Consult an allergist-immunologist or hematologist for specialized evaluation.

24-hour urine test

Measures levels of mast cell mediators (e.g., histamine metabolites) released during an activation episode. (5)

Serum tryptase test

Assesses tryptase levels in the blood, which may rise during mast cell activation. (5)

Skin biopsy

Rules out mastocytosis by examining mast cell numbers in tissue samples. (5)

Treatment

Medication options

H1 antihistamines

Blocks histamine receptors to reduce symptoms like itching and flushing. Often used as a first-line treatment. (3) (6)

H2 antihistamines

Blocks histamine receptors in the stomach, reducing gastrointestinal symptoms like nausea and acid reflux. (3) (6)

Mast cell stabilizers

Prevents mast cells from releasing mediators, reducing systemic symptoms. (3) (6)

Leukotriene inhibitors

Blocks leukotrienes, reducing inflammation and symptoms like wheezing and nasal congestion. (6)

Epinephrine (emergency use)

Used during severe reactions (anaphylaxis) to rapidly reverse symptoms. (6)

Lifestyle and self-care

Identify and avoid triggers: Common triggers include stress, temperature extremes, fragrances, alcohol, certain foods (e.g., histamine-rich foods), and medications. Keep a detailed symptom diary to recognize patterns. (7) (6)
Low-histamine diet: Some patients benefit from limiting histamine-rich foods (e.g., aged cheeses, fermented products). This should be medically supervised to ensure balanced nutrition. (7)
Stress management: Practice stress-reducing techniques like mindfulness, yoga, or meditation, as stress can trigger mast cell activation. (6)
Temperature regulation: Avoid extreme temperatures (hot or cold) that can trigger symptoms. Dress in layers and stay hydrated. (7)

Always discuss dosing and treatment changes with your own prescriber.

Possible complications

Chronic inflammation: Persistent mast cell activation can lead to ongoing inflammation, affecting multiple organs and potentially causing long-term damage. (2)
Poor quality of life: Frequent symptoms can interfere with daily activities, work, and social interactions, leading to emotional distress. (2)
Misdiagnosis: MCAS symptoms overlap with many other conditions, leading to delayed or incorrect diagnosis. (5)

When to see a doctor

Routine follow-up

If you experience recurrent symptoms affecting multiple systems (e.g., skin, gastrointestinal, cardiovascular), consult a healthcare provider for evaluation. (2)

Seek emergency care

Seek emergency care immediately if you experience symptoms of anaphylaxis, such as difficulty breathing, swelling of the throat, or a sharp drop in blood pressure. (2) (7)

Frequently asked questions

What is Mast Cell Activation Syndrome?

Mast Cell Activation Syndrome (MCAS) is a condition where mast cells release excessive chemical mediators, causing systemic allergic-type reactions. Symptoms can affect multiple body systems and range from mild to severe. (1) (2)

What are the first signs of Mast Cell Activation Syndrome?

Early signs include skin reactions (hives, flushing), gastrointestinal issues (nausea, abdominal pain), cardiovascular symptoms (low blood pressure, rapid pulse), and respiratory problems (wheezing). (2) (4)

What causes Mast Cell Activation Syndrome?

MCAS often involves genetic mutations affecting mast cell behavior and immune dysregulation. Unlike true allergies, reactions aren't always triggered by IgE antibodies. (1)

How is Mast Cell Activation Syndrome treated?

Treatment includes H1/H2 antihistamines, mast cell stabilizers, leukotriene inhibitors, and emergency epinephrine. Lifestyle adjustments like identifying triggers and stress management are also important. (3) (6)

Can Mast Cell Activation Syndrome be cured?

There is currently no cure for MCAS. Treatment focuses on symptom control through medications and lifestyle adjustments. Many patients achieve good quality of life with proper management. (6) (7)