If you’ve been given a diagnosis of hEDS or HSD, there’s a decent chance someone, at some point, has mentioned POTS and MCAS in the same breath. Maybe your cardiologist said something about mast cells, or you found a forum thread that listed all three conditions together and suddenly felt like you were reading your own medical history. The trifecta, people call it. EDS, POTS, and MCAS. Three conditions, one very complicated body.
So what’s actually going on? Are these three genuinely connected, or is it just that the people who see specialists for one tend to get tested for the others? And more importantly, if you’ve got all three, what does that actually mean for how you manage things day to day?
This one is going to be a bit of a doozy, because the honest answer is: the relationship between these three conditions is real, the overlap is well documented, but the precise mechanisms that tie them together are still being worked out. There’s a lot of noise online about this, some of it accurate, some of it not, and I want to give you a clear picture of what the research actually says rather than what people assume it says.
We’re going to cover what each condition is, how common the overlap is, what the proposed mechanisms are, what the evidence says about managing all three together, and what’s genuinely uncertain. By the end, you should have a much clearer picture of what you’re dealing with.
Quick Recap: What Are These Three Conditions?
Hypermobile EDS and Hypermobility Spectrum Disorder
hEDS and HSD are connective tissue conditions characterised by joint hypermobility, widespread pain, fatigue, and a broad range of systemic features. The connective tissue, which provides structure to joints, blood vessels, skin, and organs throughout the body, doesn’t behave the way it should. EDS affects an estimated 1 in 5000 people, with the hypermobile subtype accounting for the vast majority of diagnoses [17]. If you want the full breakdown of diagnosis and classification, our guide to EDS diagnosis has all of that.
POTS (Postural Orthostatic Tachycardia Syndrome)
POTS is a form of dysautonomia, which means it involves the autonomic nervous system not regulating things the way it should. When you stand up, your heart rate increases by 30 beats per minute or more within ten minutes, in the absence of a significant drop in blood pressure. The result is dizziness, palpitations, brain fog, fatigue, nausea, and the feeling that your body is fighting you every time you get vertical. Our POTS and exercise article goes into the management side of things in more detail.
MCAS (Mast Cell Activation Syndrome)
Mast cells are immune cells found in connective tissue throughout the body, particularly at tissue-environment interfaces: the gut, the skin, the respiratory tract. Their job is to detect threats and trigger an immune response. In MCAS, they activate too readily, release too many inflammatory mediators (histamine, tryptase, prostaglandins, leukotrienes, cytokines), and do so in response to triggers that wouldn’t bother a healthy immune system. Foods, smells, temperature changes, stress, exercise, medications [15]. The symptoms are wide-ranging because mast cells are everywhere: flushing, hives, itching, gut cramping, heart rate spikes, brain fog, headaches, and in severe cases, anaphylaxis-like episodes.
What makes MCAS particularly tricky to diagnose is that many of its mediators degrade quickly. Tryptase, which is the most stable marker, has a short half-life, which means testing needs to happen at the right time. Urinary N-methyl histamine and prostaglandin D2 can also be measured, but the diagnostic window is narrow [15].
How Common Is the Overlap?
This is where things start to get genuinely interesting, and where the data is more solid than a lot of people realise.
A 2024 retrospective study using national health records found that people with hEDS are 29.7 times more likely to be diagnosed with POTS than the general population. That’s not a minor correlation. That’s an odds ratio that tells you these conditions are clustering together for a reason, not just by chance [9]. An earlier study found that 18% of POTS patients had a comorbid EDS diagnosis compared to 0.02% in the general population [16].
When it comes to how common hEDS is in POTS specifically, a 2020 study by Miller et al. evaluated 91 POTS patients and found that 31% met the full clinical criteria for hEDS. A further 24% had generalised joint hypermobility without meeting all the hEDS criteria [4]. So somewhere between a third and over half of POTS patients have significant joint hypermobility, depending on which threshold you apply.
For MCAS and hEDS, a large retrospective analysis of over 37,000 patients found that nearly one in three people diagnosed with MCAS had a comorbid diagnosis of hEDS [11]. That figure is striking, and it held up even when controlling for demographics and hospital factors.
And all three together? A 2025 study published in Autonomic Neuroscience surveyed 84 women with HSD or hEDS and found that 58.3% had POTS, 32.1% had MCAS, and 25% had all three diagnoses simultaneously [2]. That’s one in four people with hEDS carrying all three conditions. That’s not a coincidence.
A 2025 study in Frontiers in Neurology specifically looking at young patients found similar patterns, with the prevalence of the overlap varying considerably depending on which diagnostic definitions were applied [1]. The honest message from that paper is that definition matters a lot: how strictly you define each condition changes the numbers significantly. But the association is there regardless.
Why Do They Cluster Together? The Proposed Mechanisms
Here’s where I need to be clear about what we know versus what we’re hypothesising. The overlap is real and documented. The mechanisms that explain it are proposed and plausible, but not yet confirmed experimentally. Anyone who tells you the exact biological pathway connecting these three is certain of something the research community isn’t.
The Connective Tissue Hypothesis
The most intuitive explanation is that loose, lax connective tissue causes problems in multiple systems simultaneously. Blood vessels in hEDS may also be more compliant than normal, meaning they don’t constrict efficiently when you stand up. Blood pools in the lower limbs and abdomen, the body’s baroreceptors detect a drop in effective circulating volume, and the heart races to compensate. That’s one proposed mechanism for why POTS is more common in hEDS [17].
Mast cells live in connective tissue. If the connective tissue is structurally abnormal in hEDS, it’s reasonable to hypothesise that the environment mast cells live in might be altered too. A 2022 review found that mast cell mediators, particularly histamine and tryptase, can directly disrupt connective tissue integrity through activity across multiple organ systems [6]. So there may be a bidirectional relationship here: abnormal connective tissue affects mast cell environment, and activated mast cells further disrupt connective tissue.
The mechanobiology angle adds another layer. A 2022 paper in Frontiers in Cell and Developmental Biology looked at how altered tissue mechanics in EDS might drive mast cell dysregulation through mechanobiological pathways, the physical forces on cells affecting their signalling behaviour [13]. It’s an emerging area and the evidence is largely theoretical at this stage, but the direction is interesting.
The Immune Dysregulation Hypothesis
A separate line of research suggests that hEDS may involve immune dysregulation that goes beyond connective tissue. A 2025 proteomics study found reduced complement proteins (C1QA, C3, C8a, C8b, C9) in hEDS patients compared to controls, persisting even after controlling for autoimmune conditions [18]. This suggests something intrinsic to hEDS may involve complement system dysfunction and potentially mast cell pathway activation. Whole-genome sequencing in a separate small study identified genetic variants in HLA-B and HLA-DRB1 in hEDS patients that are associated with immune regulation and mast cell hypersensitivity [10].
Lawrence Afrin, a clinician who has written extensively on MCAS, has proposed in a 2021 commentary that some cases of hEDS may actually be rooted in MCAS, with mast cell mediators driving connective tissue abnormalities rather than the other way around [14]. This is a hypothesis, not established fact, but it highlights how poorly understood the directional relationship still is.
The Autonomic-Immune Feedback Loop
MCAS and POTS may reinforce each other through an autonomic-immune feedback loop. Histamine and other mast cell mediators cause vasodilation, which worsens blood pooling and orthostatic intolerance, which worsens POTS symptoms. At the same time, the autonomic nervous system regulates immune function: low vagal tone reduces anti-inflammatory signalling, which may increase mast cell reactivity. Stress activates both the autonomic nervous system and mast cells. Exercise can trigger mast cell degranulation in MCAS, which complicates the graded exercise programmes that are standard for POTS management [5].
The AGA published a 2025 clinical practice update specifically on GI manifestations and autonomic or immune dysfunction in hEDS, and their position is appropriately cautious: the associations are observed, theoretical explanations exist, but experimental evidence of the biological mechanisms is limited and evolving [3]. That’s the honest position, and it’s worth holding onto when you read more confident claims elsewhere.
What the Evidence Doesn’t Yet Support
A 2020 review by Kucharik and Chang went through the literature systematically and found that, at the time of writing, no single experimental study had examined all three conditions together, and the evidence for a common pathophysiological mechanism between any two, let alone all three, had not been established [5]. A review by Islam, Chang and Gershwin in the same year concluded that the association appears to stem from overlapping symptom pools rather than confirmed biological mechanisms [12].
The picture has moved on since 2020, with better prevalence data and some emerging mechanistic research, but the core message holds: the overlap is real, the mechanisms are hypothesised, and you should be cautious about anyone who speaks with certainty about exactly why these three conditions travel together. That research is still being done.
What Does This Mean for Your Symptoms?
When you’ve got all three conditions, symptoms from each can amplify the others in ways that make it genuinely difficult to work out what’s causing what. This is probably the most practically useful thing to understand.
MCAS flares can trigger POTS-like symptoms. A histamine surge causes vasodilation, your blood pressure drops, your heart compensates by racing, and suddenly you’re flat on the sofa wondering whether it was the dinner, the stress, or just another POTS day. The two can look almost identical in the moment. The difference is that MCAS-driven episodes often come with skin symptoms (flushing, hives, itching) or gut symptoms alongside the cardiovascular ones, whereas a purely orthostatic POTS episode is more position-dependent.
Joint hypermobility affects autonomic function through multiple routes. The instability and pain that come with hypermobile joints are constant low-level stressors on the nervous system. Chronic pain activates the sympathetic nervous system. Sympathetic activation worsens mast cell reactivity. It’s not a neat linear chain, but the connections are there.
The quality of life impact is significant. The same study found that women with HSD/hEDS reported worse quality of life scores than patients with POTS alone, multiple sclerosis, rheumatoid arthritis, and lupus. Mean autonomic symptom scores indicated severe dysfunction across the cohort [2]. That’s not a research finding designed to make you feel hopeless. It’s a finding that justifies taking all three conditions seriously and expecting coordinated rather than siloed care.
Managing the Trifecta: What Actually Helps
This is where I want to be honest about the limits of what I can tell you in a blog post. Managing all three conditions simultaneously requires individualised, coordinated care. What follows is an overview of what the evidence supports for each strand, not a treatment protocol.
POTS Management
The non-pharmacological foundations are well established: increased fluid and salt intake (we have a dedicated article on the salt evidence if you want the detail), Compression garments, head-of-bed elevation during sleep, and a graded exercise programme. The AGA 2025 update and multiple guidelines support these as first-line approaches before pharmacological options [3].
Exercise for POTS is complicated when MCAS is also in the picture. Exercise is a known mast cell trigger for some people. This is where the order of management matters: getting MCAS reasonably stable before significantly increasing exercise load is sensible. The POTS and exercise article covers the exercise approach in detail, but the key principle is starting supine or recumbent, building slowly, and tracking responses carefully rather than pushing through.
MCAS Management
The broad approach is trigger avoidance where practical, mast cell mediator blocking, and mast cell stabilisation. The AGA 2025 update outlines that H1 and H2 antihistamines are the first-line pharmacological approach, alongside mast cell stabilisers such as cromolyn sodium and ketotifen where needed [3]. Leukotriene receptor antagonists are also used. Trigger avoidance involves identifying personal triggers, which vary considerably between people: specific foods, alcohol, temperature extremes, fragrances, mechanical stimuli, emotional distress, and certain medications [15].
Low-histamine dietary approaches are often used alongside medication. The evidence base for specific diets in MCAS is limited, but the AGA update notes that low-histamine and other elimination diets can be considered for GI symptom management, with appropriate nutritional guidance to avoid overly restrictive eating [3].
Hypermobility and Joint Stability
When it comes to the joint hypermobility side of things, the focus is on building strength and stability through the muscles that support hypermobile joints, improving proprioception and body awareness, and learning to move in ways that reduce unnecessary joint stress. This isn’t about avoiding movement, it’s about building the muscle tone and neuromuscular control that connective tissue isn’t providing. Our hypermobility and exercise article covers the principles, and the courses go into the full approach in detail.
KT taping can be useful for joint proprioception and support, particularly during more demanding activities. There’s more on that in our KT tape guide. Compression garments are worth considering for both the hypermobility and POTS sides of things.
The Sequencing Problem
One of the most useful things to understand when managing all three is that the order in which you address things matters. Starting an aggressive exercise programme when MCAS is poorly controlled can trigger significant flares. Expecting POTS exercise protocols to work if you’re repeatedly crashing from mast cell reactions is unrealistic. Building a reasonable baseline of mast cell stability, then working on POTS conditioning, while gradually building musculoskeletal strength and stability in parallel, is a more logical approach than trying to do everything simultaneously at full intensity.
This is not a linear process. You will have flares. The aim isn’t to eliminate all symptoms before you start moving; it’s to find a sustainable baseline that allows you to make gradual, consistent progress without repeatedly crashing. If you want to read more about the pacing side of this, our pacing guide covers the principles in detail.
Getting Diagnosed With All Three
One of the consistent findings across the research is that these conditions are underdiagnosed, misdiagnosed, and diagnosed late. People with hEDS are 29.7 times more likely to have POTS than the general population [9], but how many of them know about it? How many have had a simple active stand test done, let alone a tilt table? The overlap with conditions that can mimic these symptoms makes getting the right diagnosis even harder.
The AGA 2025 guidance is helpful here: testing for POTS and MCAS should be targeted to people presenting with relevant clinical manifestations, not done universally in every hEDS patient. But the clinical manifestations of all three overlap considerably, which means a clinician needs to be actively thinking about the triad to test appropriately. Finding a practitioner familiar with hEDS, POTS, and MCAS is genuinely difficult, and multidisciplinary input (rheumatology, cardiology or neurology, allergy/immunology) is often needed [3].
If you’re navigating the diagnostic journey, our EDS diagnosis guide and our MCAS explainer might be useful starting points. If you’re also navigating the emotional impact of medical trauma that often comes with late diagnosis, that’s worth acknowledging too. For POTS, the POTS exercise article has information on the diagnostic criteria and what the testing process involves.
The Long COVID Connection
It’s worth a brief mention here because it comes up a lot. A 2024 review found that hypermobility has been detected in 30 to 57% of patients with ME/CFS, fibromyalgia, POTS, and long COVID [7]. The proposed shared pathophysiology involves immune dysregulation, autonomic dysfunction, connective tissue vulnerability, and mast cell involvement. For people whose trifecta symptoms began or significantly worsened after a COVID-19 infection, this overlap is clinically relevant. The coat hanger pain pattern many POTS patients experience, caused by poor blood flow to the neck and shoulder muscles on standing, is a useful symptom marker to know about. It doesn’t change the management principles significantly, but it does provide some context for why post-viral onset is so common in this community.
Frequently Asked Questions
Not necessarily. Research shows that around 58% of people with HSD/hEDS in some studies have POTS, and around 32% have MCAS. Roughly 25% appear to have all three. However, these figures come from clinical populations, people already attending specialist services, which may not reflect the full hEDS population. The overlap is significant but not universal.
For people in whom MCAS is driving autonomic dysfunction through histamine-mediated vasodilation and mast cell-related POTS flares, stabilising mast cell activity can improve POTS symptoms. However, POTS in hEDS is multifactorial. Mast cell stabilisation is one piece of the puzzle rather than the whole answer, and the evidence base for specific combinations is still limited.
Several reasons. All three conditions have overlapping symptoms. Diagnostic criteria for each have changed over time and are applied inconsistently. MCAS markers degrade quickly making testing timing-sensitive. POTS often requires a tilt table test or active stand test that isn’t done routinely. hEDS has no genetic marker and diagnosis relies on clinical criteria. Finding a clinician familiar with all three is genuinely difficult.
Exercise remains important, but the approach needs careful calibration. MCAS-triggered exercise intolerance is a real concern for some people, and pushing through mast cell flares is counterproductive. The evidence-based approach for POTS starts with recumbent or semi-recumbent exercise before progressing to upright activity. Building in parallel with MCAS management rather than treating them completely separately tends to produce better results.
A purely orthostatic POTS episode is strongly position-dependent: it’s brought on by standing and improves with lying down. An MCAS-driven episode often includes additional symptoms such as flushing, hives, itching, gut cramping, or a feeling of sudden systemic reaction, and may not resolve simply with lying down if the mast cell trigger is still active. In practice, they frequently overlap, and distinguishing them can be difficult without careful symptom tracking.
The Bottom Line
The trifecta of hEDS, POTS, and MCAS is a real, documented phenomenon. One in four people with hEDS in clinical populations carries all three diagnoses [2], and hEDS patients are nearly 30 times more likely to have POTS than the general population [9]. The biological mechanisms that tie all three together are plausible, well-hypothesised, and supported by some emerging research, but direct experimental confirmation is still limited [5][12]. The picture is made more complex still by overlaps with the mast cell-fibromyalgia connection and heart rate variability patterns that are worth exploring separately.
What that means practically is this: if you have one of these conditions, it’s worth knowing about the others. If you have symptoms that don’t fit neatly into whichever diagnosis you’ve got, it may be worth asking whether the other two are in the picture. And if you’re managing all three, expect the process to require coordination between different specialties, careful attention to sequencing, and a lot of patience with a body that is doing a genuinely complicated juggling act.
If this is something you’re navigating and you want structured support with the movement and rehabilitation side of things, that’s where the courses and consultations come in. We slow it all down and build the full picture. It’s not quick, but it works.
— The Fibro Guy Team —
