Mast Cell Activation Syndrome (MCAS)
Understanding a Complex Immune Dysregulation Condition
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Mast Cell Activation Syndrome (MCAS) is an increasingly recognized immune condition that can cause a wide range of chronic, multi-system symptoms. Individuals with MCAS often experience unpredictable reactions affecting the skin, digestive system, nervous system, cardiovascular system, and respiratory tract, making the condition difficult to identify and manage.
At Keystone Total Health, Dr. Martin Hart, DC, and Dr. Koji Aoki, DC frequently work with individuals navigating complex chronic illness, including immune dysregulation patterns consistent with MCAS. Our clinic is located in Columbia, Tennessee, serving the greater Nashville area, and welcoming clients from across the United States seeking a root-cause, functional perspective.
What Is Mast Cell Activation Syndrome (MCAS)?
Mast Cell Activation Syndrome (MCAS) is a condition characterized by abnormal or excessive activation of mast cells, a type of immune cell involved in inflammatory and allergic responses.
Mast cells play an essential role in immune defense, wound healing, and communication between the immune and nervous systems. In MCAS, these cells release inflammatory mediators—such as histamine, cytokines, prostaglandins, and leukotrienes—inappropriately or excessively, leading to chronic symptoms across multiple systems.
Unlike classic allergies, MCAS reactions may occur without a clear trigger and may not show up on standard allergy testing.
What Do Mast Cells Do?
Mast cells are found throughout the body, particularly in tissues that interface with the environment, including:
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Skin
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Gastrointestinal tract
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Respiratory system
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Blood vessels
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Nervous system
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Their role includes:
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Regulating inflammatory responses
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Supporting immune defense
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Communicating with nerves and blood vessels
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Responding to stress, injury, or perceived threats
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When mast cell signaling becomes dysregulated, the result can be chronic inflammation, hypersensitivity, and system-wide symptoms.
Common Symptoms of MCAS
MCAS symptoms vary widely and often fluctuate, which is one reason the condition is frequently overlooked.
Skin & Allergic-Type Symptoms
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Flushing or redness
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Hives or rashes
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Itching
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Temperature sensitivity
Digestive Symptoms
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Abdominal pain
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Bloating
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Diarrhea or constipation
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Nausea
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Food sensitivities
Digestive symptoms often overlap with underlying gut and digestive issues and intestinal inflammation.
Neurological & Cognitive Symptoms
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Brain fog
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Headaches or migraines
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Dizziness
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Anxiety or panic-like sensations
Cardiovascular & Autonomic Symptoms
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Rapid heart rate
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Lightheadedness
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Blood pressure fluctuations
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Exercise intolerance
Respiratory Symptoms
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Shortness of breath
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Chest tightness
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Nasal congestion
Because mast cells interact with nearly every body system, symptoms may appear unrelated at first glance.
What Triggers Mast Cell Activation?
In MCAS, mast cell activation may be triggered by a wide range of internal or external factors, including:
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Certain foods or food additives
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Environmental exposures
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Stress or emotional strain
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Temperature changes
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Infections or immune challenges
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Hormonal shifts
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Importantly, mold illness and Lyme disease are commonly associated with mast cell activation due to their impact on immune signaling and inflammatory burden.
MCAS, Mold Illness, and Lyme Disease: A Strong Overlap
Dr. Hart and Dr. Aoki frequently observe MCAS-like symptom patterns in individuals with mold illness (CIRS) and Lyme disease
Both mold biotoxins and chronic infections can:
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Activate mast cells directly
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Increase inflammatory mediator release
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Disrupt nervous system regulation
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Lower the body’s tolerance threshold
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This overlap helps explain why individuals with mold or Lyme often develop heightened sensitivities, food reactions, or histamine-type symptoms over time.
MCAS and Autoimmune or Chronic Inflammatory Conditions
MCAS is often seen alongside autoimmune and inflammatory conditions such as:
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Hashimoto’s thyroiditis
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Celiac disease
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Multiple Sclerosis (MS)
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Chronic fatigue syndromes
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In these cases, mast cell activation may contribute to ongoing immune signaling, inflammation, and symptom persistence, rather than being a separate issue.
How MCAS Is Evaluated
MCAS can be challenging to evaluate because standard allergy tests often fail to detect it. Evaluation typically involves:
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A detailed symptom history across multiple systems
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Identification of reaction patterns and triggers
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Functional lab testing when appropriate
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Consideration of overlapping conditions such as mold illness, Lyme disease, gut dysfunction, and mineral imbalances
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At Keystone Total Health, evaluation focuses on patterns and contributors, rather than a single marker or diagnosis.
Why MCAS Is Often Missed
MCAS is frequently overlooked because:
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Symptoms mimic allergies, anxiety, or IBS
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Reactions may be inconsistent
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Lab findings may be subtle or variable
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Providers may focus on one system at a time
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A root-cause, systems-based approach helps connect these seemingly unrelated symptoms into a more coherent picture.
Serving Columbia, TN, Nashville, and Clients Nationwide
Keystone Total Health is located in Columbia, Tennessee, serving individuals throughout the greater Nashville area and welcoming clients from across the country seeking comprehensive evaluation for complex immune and inflammatory conditions.
MCAS (Mast Cell Activation Syndrome) FAQ
Mast Cell Activation Syndrome can be confusing and overwhelming, especially when symptoms affect multiple body systems and seem unpredictable. The following questions address common concerns about MCAS, its symptoms, triggers, and how it often overlaps with mold illness, Lyme disease, and other complex chronic conditions
What is Mast Cell Activation Syndrome (MCAS)?
Mast Cell Activation Syndrome (MCAS) is a condition in which mast cells release inflammatory mediators too frequently or inappropriately, leading to chronic, multi-system symptoms. Unlike traditional allergies, MCAS reactions may occur without a clear trigger and often affect the nervous system, gut, skin, cardiovascular system, and immune function.
What are the most common symptoms of MCAS?
Common MCAS symptoms include flushing, hives, itching, digestive discomfort, bloating, diarrhea, brain fog, headaches, dizziness, rapid heart rate, anxiety-like symptoms, and sensitivity to foods, chemicals, or environmental exposures. Symptoms often fluctuate and may worsen with stress or illness.
Can MCAS cause brain fog and neurological symptoms?
Yes. Mast cells interact closely with the nervous system. In MCAS, excessive mediator release can contribute to brain fog, headaches, dizziness, sensory sensitivity, mood changes, and sleep disruption. These neurological symptoms often overlap with patterns seen in chronic inflammatory conditions.
How is MCAS different from allergies?
While allergies involve a specific immune response to a known allergen, MCAS involves inappropriate mast cell activation that may occur without a clear allergen. Standard allergy testing is often normal in individuals with MCAS, which can make the condition harder to identify.
What triggers mast cell activation?
Triggers vary by individual and may include certain foods, food additives, environmental exposures, temperature changes, stress, infections, hormonal shifts, or chemical sensitivities. In many cases, mast cells become more reactive over time as overall inflammatory burden increases.
Is MCAS linked to mold illness or Lyme disease?
Yes. MCAS frequently overlaps with mold illness (CIRS) and Lyme disease. Mold biotoxins and chronic infections can activate mast cells, lower tolerance thresholds, and worsen inflammatory signaling. This overlap is common in individuals with complex chronic illness.
Learn more about related conditions:
Can MCAS affect digestion and food tolerance?
Yes. Mast cells are abundant in the gastrointestinal tract. MCAS can contribute to food sensitivities, bloating, abdominal pain, diarrhea, nausea, and reactions to histamine-rich foods. These symptoms often overlap with underlying gut and digestive issues.
How is MCAS evaluated?
MCAS evaluation typically involves a detailed review of symptoms across multiple systems, identification of trigger patterns, and consideration of overlapping conditions such as mold illness, Lyme disease, gut dysfunction, and mineral imbalances. No single test confirms MCAS in all cases, so pattern recognition is key.
Why is MCAS often missed or misdiagnosed?
MCAS is frequently overlooked because symptoms can mimic anxiety, IBS, allergies, or autoimmune conditions. Lab findings may be inconsistent, and symptoms often fluctuate. A systems-based, root-cause approach helps connect these patterns more clearly.
Who should consider an MCAS-focused evaluation?
An MCAS-focused evaluation may be helpful for individuals who experience frequent unexplained reactions, multiple food or chemical sensitivities, chronic inflammation, mold exposure, Lyme disease, or persistent symptoms that have not been fully explained by conventional testing.
Resources & Further Reading
The following resources provide additional scientific and clinical information on Mast Cell Activation Syndrome:
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The Mast Cell Disease Society (TMS): https://tmsforacure.org
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National Institute of Allergy and Infectious Diseases (NIAID): https://www.niaid.nih.gov
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Afrin LB. Never Bet Against Occam: Mast Cell Activation Disease and the Modern Epidemics of Chronic Illness and Medical Complexity
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Weinstock LB et al. Mast Cell Activation Syndrome: A Review – PubMed
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Valent P et al. Definitions, Criteria and Global Classification of Mast Cell Disorders – World Allergy Organization Journal