When Your Immune System Won’t Turn Off
If your body seems to overreact to foods, smells, heat, stress, medications, or “nothing at all,” you’re not imagining it. Many people with EDS, hypermobility and POTS also live with Mast Cell Activation Syndrome (MCAS). MCAS can make your body feel unpredictable, reactive, and unsafe — even on your best days. That’s why we are going to go through Mast Cell Activation Syndrome (MCAS) Symptoms, Testing and the Basics.
Understanding what’s happening inside your body is the first step toward taking control again.
What Mast Cells Actually Do
Mast cells are immune system cells found throughout the body. Think of them like security guards. They watch for danger and release chemical messengers — called mediators — to help protect you. Histamine is the most well-known mediator, but mast cells release over 200 different chemicals. Which is why MCAS is so difficult to diagnose and manage. Imagine how many different combinations you could have with varying levels of 200 different chemicals.
In a healthy body, this system helps heal wounds and fight infections. In MCAS, the system is overactive and fires even when it shouldn’t.
What Happens in MCAS
With MCAS, mast cells release these 200+ chemical mediators too easily and too often. This causes widespread inflammation across many systems of the body. Symptoms often come in flares and may worsen after illness, surgery, emotional stress, or physical strain.
Triggers vary from person to person. Symptoms can show up in one system or several at once — and they can change from day to day.
Common Symptoms
MCAS can affect nearly every part of the body. Some people experience flushing, itching, rashes, hives, or swelling. Others deal with nausea, abdominal pain, reflux, diarrhea, dizziness, headaches, brain fog, palpitations, shortness of breath, or fatigue. Others still may experience issues with blood clotting then bleeding too much, neurologic symptoms that come and go. Basically anything that those 200+ chemicals can affect in the body could go awry.
Many people feel like their body is “on edge” even when they are resting. The wide range of potential symptoms coupled with the fact that these symptoms come and go based on if the mast cells are being triggered is why MCAS is often missed.
How MCAS Is Tested
There is no single perfect test for MCAS. Blood and urine tests may look for elevated mast cell mediators like tryptase, histamine, prostaglandins, or leukotrienes. But these tests are not done at every clinic and are so short lived that if the laboratory is not following the protocols perfectly (meaning putting the blood on ice immediately or running the test immediately) then the tests will not be accurate. These tests are most helpful when done during a flare but even normal results that come while you are in a flair does not rule out MCAS.
Diagnosis is based on symptoms, lab patterns, and how you respond to treatment.
Why MCAS Often Shows Up with EDS and POTS
Hypermobility, POTS, and MCAS commonly occur together. While research is still evolving, many people live with all three to varying degrees. This overlap can explain why symptoms feel complex, unpredictable, and multi-system.
If you have EDS or POTS and unexplained allergic-type symptoms, MCAS deserves consideration.
The Takeaway
MCAS is not “just allergies.”
It is a systemic immune condition that deserves proper care and understanding.
Your symptoms are real.
And your body is not broken — it’s just reacting too loudly.
Share Your Story
Have you noticed certain triggers that cause flares for you? What symptoms show up first when your body reacts?
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Warm regards,
The Hypermobile Solutions Team
References
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What is eds?. The Ehlers Danlos Society. https://www.ehlers-danlos.com/what-is-eds/
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Cox, C. (2022). Holding it all together when you’re Hypermobile. Journey2Joy
Afrin, L. B. (2016). Never bet against Occam: Mast cell activation disease and the modern epidemics of chronic illness and medical complexity. Sisters Media, LLC.
Freeman, K., Goldstein, D. S., & Thompson, C. R. (2025). The dysautonomia project: Understanding autonomic nervous system disorders (2nd ed.). Bardolf.
Disclaimer
This blog is for general informational purposes only and does not constitute the practice of medicine, nursing, or other professional health care services, including the giving of medical advice, and no provider/patient relationship is formed. The use of information on this blog or materials linked from this blog is at the user’s own risk. The content of this blog is not intended to be a substitute for professional medical advice, diagnosis, or treatment. Users should not disregard or delay in obtaining medical advice for any medical condition they may have and should seek the assistance of their health care professionals for any such conditions.