Why Do hEDS, POTS, and MCAS Occur Together?
If you have hypermobile Ehlers-Danlos Syndrome (hEDS), postural orthostatic tachycardia syndrome (POTS), or mast cell activation syndrome (MCAS), you may have received each diagnosis from a different specialist, years apart, as though they were separate, unrelated problems.
They are not separate. They share a common biological root, and understanding that connection is the key to getting care that actually helps.
What Are hEDS, POTS, and MCAS?
Hypermobile Ehlers-Danlos Syndrome (hEDS) is the most common subtype of Ehlers-Danlos Syndrome, a group of inherited connective tissue disorders. Unlike other EDS subtypes, hEDS has no known genetic marker and is diagnosed clinically. Its hallmarks include generalized joint hypermobility, chronic musculoskeletal pain, skin that may be soft or stretchy, and a long list of systemic symptoms affecting the gut, nervous system, and immune response.
A 2025 population-level study using data from over 23 million U.S. patients found hEDS prevalence to be approximately 1 in 800, significantly higher than the previously recognized estimate of 1 in 3,100, with 84% of diagnosed patients being female. (Pearson et al., medRxiv, 2025)
Postural Orthostatic Tachycardia Syndrome (POTS) is a form of dysautonomia in which the heart rate increases abnormally (by 30 or more beats per minute) when moving from lying or sitting to standing. Symptoms include dizziness, lightheadedness, palpitations, exercise intolerance, brain fog, and fatigue. Diagnosis is frequently delayed: one review found an average diagnostic journey of nearly 5 years for POTS patients (Cognitive FX, 2026).
Mast Cell Activation Syndrome (MCAS) involves mast cells, immune cells distributed throughout the body's connective tissue, releasing inflammatory mediators inappropriately. This triggers a wide range of seemingly unrelated symptoms: flushing, hives, gut cramping, near-anaphylaxis reactions, brain fog, chemical sensitivities, and more. Diagnosis is complicated by inconsistent criteria and the fleeting nature of mast cell biomarkers.
Why These Three Conditions Cluster Together
The overlap among hEDS, POTS, and MCAS is not coincidence or diagnostic fashion. The relationship between these three conditions is now firmly established in the medical literature. A 2019 paper in the American Journal of Medical Genetics formally examined this relationship, and subsequent research has continued to map the mechanisms that link them. (PubMed 31267471)
A 2025 study published in Frontiers in Neurology reviewed 100 young patients who met POTS criteria and assessed the co-occurrence of hypermobility disorders and MCAS. Depending on the diagnostic criteria applied, joint hypermobility disorders occurred in 13-34% of POTS patients, and MCAS occurred in 2-87%. The authors concluded that using overly strict diagnostic criteria for these co-occurring conditions "misses opportunities for potential therapeutic strategies." (Raja & Pandey, Frontiers in Neurology, 2025)
The clinical picture is this: these three conditions share the same biological substrate, collagen and connective tissue, and they amplify each other through a cycle of structural, autonomic, and immune dysfunction.
The Role of Connective Tissue
Collagen is the structural protein that holds the body together. In hEDS, the collagen matrix is abnormally lax or disorganized. This creates instability far beyond the joints.
Blood vessel walls are made largely of collagen. When vessel walls are lax, veins cannot maintain adequate tone, and blood pools in the lower body upon standing. The autonomic nervous system detects this drop in venous return and compensates by accelerating the heart rate, that is POTS.
Mast cells live in connective tissue throughout the body. In an unstable connective tissue environment, mast cells may be more susceptible to mechanical stress, microenvironmental changes, and immune triggers. Histamine and other mast cell mediators, in turn, cause vasodilation and further reduce blood pressure, worsening orthostatic intolerance and fueling a vicious cycle. As one analysis put it, the relationship may be bidirectional: "abnormal connective tissue affects mast cell environment, and activated mast cells further disrupt connective tissue." (The Fibro Guy, 2024)
The gastrointestinal tract, which is lined with collagen and densely populated with mast cells, is another convergence point. Slowed gut motility, intestinal permeability, SIBO, and food sensitivities are extremely common in this population, and each of these problems can trigger further mast cell activation and autonomic dysregulation.
How POTS Develops in hEDS
POTS in the context of hEDS is thought to arise through several pathways:
Venous pooling. Lax blood vessel walls allow blood to collect in the legs and abdomen upon standing. The heart accelerates to compensate for reduced blood returning to the chest. This is the primary mechanism in most hEDS-associated POTS.
Small fiber neuropathy. Some patients with hEDS develop damage to small autonomic nerve fibers that regulate vascular tone, compounding the pooling problem.
Reduced blood volume. Dysregulated fluid balance in hEDS patients can result in chronically low plasma volume, making the orthostatic challenge worse.
Mast cell contribution. Histamine released by mast cells is a potent vasodilator. When MCAS is active, histamine further drops peripheral vascular resistance, directly worsening POTS symptoms.
This layered causation is why treating POTS with only beta-blockers or saline rarely resolves the full picture. Without addressing the connective tissue and mast cell components, symptom management remains incomplete.
How MCAS Connects to the Trifecta
Mast cells are not random bystanders. They sit at the intersection of the immune, autonomic, and structural systems, releasing dozens of mediators that affect everything from heart rate and blood pressure to gut motility, pain sensitivity, and brain function.
In patients with hEDS, several factors may lower the threshold for mast cell activation:
Mechanical stress on connective tissue can directly activate mast cells
Autonomic instability (POTS flares, adrenaline surges) triggers mast cell degranulation
Gut dysbiosis and intestinal permeability, both common in hEDS, provide continuous immune stimulation
Environmental triggers including mold, chemicals, and dietary histamine are tolerated poorly when mast cells are already primed
Researchers have noted that mast cell mediators such as tryptase and histamine may themselves contribute to connective tissue remodeling, suggesting the relationship flows in both directions. (PoTS UK)
This bidirectional amplification is what makes the trifecta so debilitating. Each system feeds dysfunction into the others, and the total burden is greater than any single condition alone.
The Long COVID Link
Patients with the hEDS-POTS-MCAS trifecta are disproportionately vulnerable to post-viral syndromes, particularly Long COVID.
The 2025 population study of over 23 million U.S. patients found that individuals with hEDS were significantly more likely to develop Long COVID following SARS-CoV-2 infection compared to matched controls. Notably, those with overlapping POTS, MCAS, or ME/CFS had the highest Long COVID rates of all. The study also found that many patients received their first hEDS diagnosis only after COVID-19, suggesting that viral illness may unmask or accelerate previously unrecognized connective tissue disease. (Pearson et al., medRxiv, 2025)
This makes clinical sense. COVID-19 is known to trigger autoimmunity, mast cell activation, and dysautonomia in susceptible individuals. For someone with underlying hEDS and a primed mast cell system, a significant viral illness can push the trifecta from subclinical to fully symptomatic.
For patients who felt healthy until a viral infection triggered a cascade of new symptoms, this research provides validation and a biological explanation.
The Diagnostic Delay Problem
Most patients with hEDS receive more than 10 different diagnoses before arriving at the correct one. (The EDS Clinic) POTS patients wait an average of nearly 5 years for a diagnosis. (Cognitive FX, 2026) MCAS frequently goes unrecognized for decades.
The delay happens for several reasons:
Specialist silos. Rheumatologists see joint problems. Neurologists see POTS. Allergists see mast cell reactions. Few connect the dots across systems.
Normal standard tests. Routine blood work, imaging, and cardiac workups often return normal results, leading to dismissal rather than deeper investigation.
Criteria strictness. Overly rigid diagnostic criteria for MCAS and hEDS mean that many clinically affected patients are told they "don't quite meet" the threshold.
Gender bias. Approximately 80% of hEDS patients are female, and the research consistently shows that women with complex multi-system illness wait longer for diagnoses and are more likely to have their symptoms attributed to anxiety. (Pearson et al., medRxiv, 2025)
The result is a population of patients who are genuinely ill, medically complex, and frequently told there is nothing wrong.
What a Root-Cause Approach Looks Like
Effective care for the hEDS-POTS-MCAS trifecta requires a clinician who can hold the whole picture. The goal is not to suppress each symptom in isolation, but to reduce the total inflammatory and structural burden across all three systems simultaneously.
A root-cause approach typically includes:
Stabilizing mast cell reactivity first. Reducing the baseline mast cell load lowers the inflammatory tide driving much of the autonomic and structural dysfunction. This involves identifying dietary and environmental triggers, low-histamine nutritional support, targeted supplementation (quercetin, vitamin C, DAO enzyme), and prescription mast cell stabilizers when warranted.
Supporting blood volume and autonomic tone. Sodium and fluid protocols, evidence-based exercise reconditioning (starting from a position of safety rather than pushing through post-exertional malaise), compression strategies, and botanical and nutritional nervous system support.
Connective tissue and joint stabilization. Targeted nutritional cofactors for collagen synthesis, referral to physical therapists with hEDS-specific experience, and regenerative options such as prolozone for painful or unstable joints.
Treating overlapping conditions. Co-occurring gut dysfunction, mold illness, chronic infections, and autoimmune patterns all contribute to the trifecta's severity and must be addressed as part of the same treatment plan.
Monitoring and adjusting. The trifecta is dynamic. Hormonal shifts, infections, environmental exposures, and stress all modulate symptoms. Treatment requires an ongoing relationship with a clinician who tracks the whole picture over time.
Working With a Specialist in Seattle
Finding a provider who understands the hEDS-POTS-MCAS connection, rather than treating each condition in isolation, makes a significant difference in outcomes and in the experience of being a patient.
Dr. Katherine Carvlin, ND, is a naturopathic and environmental medicine physician at Full Circle Natural Medicine in Seattle, WA, specializing in the hEDS-POTS-MCAS trifecta and complex chronic illness. She offers individualized, evidence-informed care for patients who have spent years collecting diagnoses without a clear treatment roadmap.
If you are in the Seattle area/Washington State and looking for a clinician who will connect the dots, schedule an appointment with Dr. Carvlin today.
This article is for educational purposes and does not constitute medical advice. Please work with a qualified healthcare provider for diagnosis and treatment of any medical condition.