Mast Cell Activation Syndrome (MCAS)

Mast Cell Activation Syndrome (MCAS) is a complex immune condition where mast cells—specialized immune cells found throughout the body—release excessive inflammatory chemicals without appropriate triggers or in disproportionate amounts. Unlike mastocytosis (where there are too many mast cells), MCAS primarily involves dysfunction in normal mast cell populations.

These mast cells, which normally help protect us from infection and participate in inflammatory processes, instead create a cascade of inappropriate responses affecting multiple body systems. The released mediators (including histamine, cytokines, prostaglandins, and leukotrienes) can affect virtually any organ system, leading to fluctuating and sometimes unpredictable symptoms.

MCAS is increasingly recognized as part of a “chronic constellation” of conditions that frequently co-occur with neurodivergent conditions, connective tissue disorders, and autonomic nervous system dysfunction.

Key Aspects

• Core Characteristics

  • Inappropriate release of mast cell mediators without proper triggers

  • Symptoms affecting multiple body systems that fluctuate in type and severity

  • Triggers may include foods, medications, environmental factors, stress, temperature changes, and physical stimuli

  • Difficult to diagnose due to symptom overlap with other conditions

  • Often part of a “trifecta” or “pentad” of co-occurring conditions including hypermobility disorders (like Ehlers-Danlos Syndrome) and dysautonomia (like POTS)

• Symptom Presentation

  • Neurological: brain fog, headaches, memory issues, difficulty concentrating

  • Gastrointestinal: abdominal pain, nausea, diarrhea, food sensitivities, bloating

  • Dermatological: flushing, hives, itching, rashes, swelling

  • Respiratory: congestion, wheezing, throat tightness, shortness of breath

  • Cardiovascular: tachycardia, blood pressure fluctuations, dizziness, lightheadedness

In Their Own Words

When I’m having an MCAS flare, it feels like my entire body is betraying me. One minute I’m fine, the next I’m covered in hives, my stomach is in knots, and my brain feels like it’s wrapped in cotton. The unpredictability is almost as exhausting as the symptoms themselves. What’s most frustrating is trying to explain to people why I can eat a food one day with no problems, but the next day it sends me into a reaction. It’s like my body is constantly changing the rules on me.

As someone with both autism and MCAS, I’ve noticed my sensory sensitivities get dramatically worse during flares. Sounds that are normally just annoying become physically painful, and textures that I usually tolerate become completely unbearable. It’s like all my normal coping mechanisms get overridden when my mast cells are activated.

In Everyday Life

MCAS manifests in countless daily challenges that might seem unrelated but actually stem from the same underlying condition:

• A person develops flushing, heart palpitations, and anxiety after eating fermented foods, only to be told it’s “just anxiety”

• Someone experiences severe brain fog and fatigue after exposure to certain perfumes or cleaning products

• A child has varying reactions to the same foods on different days, making meal planning extremely difficult

• An individual finds their digestive symptoms, joint pain, and cognitive difficulties all worsen simultaneously during stressful periods

• A person with both ADHD and MCAS notices that their executive function difficulties become significantly worse during allergic-type reactions

Why This Matters

MCAS matters because it represents a missing piece in understanding many neurodivergent experiences. The growing evidence of overlap between MCAS, hypermobility, and neurodivergence suggests shared underlying mechanisms that connect brain function, immune response, and connective tissue.

For many neurodivergent individuals, identifying and addressing MCAS can lead to significant improvement in overall functioning. Understanding these connections helps explain why certain environmental factors might worsen cognitive symptoms, sensory sensitivities, or emotional regulation.

Most importantly, this knowledge shifts the focus from viewing various symptoms as separate conditions to understanding them as part of an interconnected system, leading to more effective treatments and accommodations.

Co-occurrences

• Autism (estimated 30-50% higher prevalence than general population)

• ADHD (estimated 25-40% higher prevalence than general population)

• Ehlers-Danlos Syndrome/Hypermobility Spectrum Disorders (30-66%)

• Postural Orthostatic Tachycardia Syndrome (POTS) (30-60%)

• Fibromyalgia (20-40%)

• Autoimmune conditions (15-30%)

Historical Development

• 1990s-2000s: Recognition of non-mastocytosis mast cell disorders begins to emerge in medical literature

• 2007: Term “mast cell activation syndrome” first appears in medical literature

• 2010-2011: International consensus diagnostic criteria for MCAS established

• 2013-2015: Connection between MCAS and Ehlers-Danlos Syndrome increasingly recognized

• 2016-present: Growing research documenting the relationship between mast cell disorders, joint hypermobility, dysautonomia, and neurodivergent conditions

• 2020-present: Increasing recognition of the “chronic constellation” or “pentad” of related conditions

Related Concepts

• Chronic Constellation

• The Trifecta (EDS, POTS, MCAS)

• Central Sensitivity Syndromes

• Joint Hypermobility/Ehlers-Danlos Syndrome

• Dysautonomia/POTS

• Sensory Processing Differences

• Interoception

• Central Sensitization

• Spoon Theory

References

• Afrin, L. B., & Molderings, G. J. (2014). A concise, practical guide to diagnostic assessment for mast cell activation disease. World Journal of Hematology, 3(1), 1-17.

• Boren, R. (2024). Chronic Constellation. Stimpunks Foundation. https://stimpunks.org/glossary/chronic-constellation/

• Casanova, E. L., et al. (2019). Autism and environmental influences: Complex multilevel models in search of simple answers. Journal of Autism and Developmental Disorders, 49(8), 3128-3141.

• Csecs, J. L., et al. (2022). Joint hypermobility, dysautonomia and neurodevelopmental conditions: An online cross-sectional survey of patient-reported symptoms and outcomes. American Journal of Medical Genetics Part A, 188(4), 1219-1231.

• Eccles, J., et al. (2021). Joint hypermobility links neurodivergence to dysautonomia and pain. Frontiers in Psychiatry, 12, 786916.

• Maxwell, A. J. (2023). The Pentad Assessment & Management. [Presentation]. Ehlers-Danlos Society Conference.

• Mast Cell Action. (2024). Understanding mast cell activation syndrome. https://www.mastcellaction.org/

• The Mast Cell Disease Society. (2024). Mast Cell Activation Syndromes. https://tmsforacure.org/overview/

• Theoharides, T. C., et al. (2019). Mast cells, neuroinflammation and pain in fibromyalgia syndrome. Frontiers in Cellular Neuroscience, 13, 353.

• Weinstock, L. B., et al. (2021). Mast cell activation syndrome: a primer for the gastroenterologist. Digestive Diseases and Sciences, 66(4), 965-982.