If you’re experiencing symptoms like dizziness, flushing, fatigue, palpitations, gastrointestinal issues, or brain fog, it can be difficult to tell what is causing what, especially when symptoms come and go in flare-ups. Some people are diagnosed with MCAS, some with POTS, and some eventually discover they may be dealing with both.

MCAS and POTS are understood to often occur together, and the conditions are being studied to understand why. That research is still evolving, which can sometimes leave people feeling confused about their own health and experiences.

In this article, we’ll unpack what may link MCAS and POTS, explore shared symptoms, and outline practical ways to track and manage them, so you can work more effectively with your healthcare team.

What is the link between MCAS and POTS?

Mast cell activation syndrome (MCAS) is a condition where mast cells, immune cells that release chemicals like histamine, become overly reactive. This overreactivity can cause symptoms such as flushing, hives, or gastrointestinal discomfort, even without a clear trigger.

Postural orthostatic tachycardia syndrome (POTS) is a form of autonomic dysfunction where heart rate increases excessively upon standing. People with POTS often experience dizziness, palpitations, or fainting when they move to an upright position.

Research into a possible link between MCAS and POTS is ongoing. Some studies and clinical observations suggest they may co-occur more often than expected, and that mast cell activity could influence blood vessel tone or autonomic responses. However, these mechanisms are not fully understood, and evidence remains limited.

To make matters even more complex, some clinicians have observed overlap in patients with Ehlers-Danlos syndrome (EDS). This is sometimes informally described as the “trifecta” of MCAS, POTS, and EDS.

While no single explanation fits everyone, recognizing that these conditions can occur together may help guide more informed discussions with your healthcare provider.

Possible shared symptoms of MCAS and POTS

Because MCAS and POTS can affect multiple body systems, some people notice a mix of overlapping symptoms or symptoms that occur alongside each other. Not everyone will have all of them, and their severity can vary from day to day. Tracking when and how these symptoms appear can help uncover your personal patterns and triggers.

#1: Dizziness or lightheadedness

In POTS, dizziness and lightheadedness can happen when standing up because the heart rate increases more than usual.

In MCAS, the release of chemicals such as histamine can affect blood vessel tone, which may contribute to feeling faint or unsteady in some people.

‍#2: Fatigue and energy fluctuations

Fatigue is common in POTS and may also be experienced in some people with MCAS. However, it’s not a primary symptom.

In POTS, it is often linked to how the body regulates blood flow and heart rate. In MCAS, fatigue may occur during or after symptom flare-ups.

#3: Gastrointestinal distress

Abdominal pain, nausea, and bloating can affect people with either condition.

In MCAS, the release of chemicals such as histamine may irritate the digestive system. In POTS, the body’s autonomic functions that control digestion may not work as smoothly, which can slow the movement of food through the gut. Together, these effects can make eating feel unpredictable.

#4: Brain fog and concentration issues

Some people describe a feeling of mental “cloudiness” or trouble concentrating, often called brain fog.

In POTS, studies suggest this may happen because blood flow to the brain can drop temporarily when standing. In MCAS, chemical mediators such as histamine and cytokines may affect how the brain’s signaling works, which can also make thinking or focusing feel harder.

Brain fog can be hard to describe. No two people will necessarily experience it in the same way. When it comes to explaining this symptom to your doctor, it may help to bring along a detailed record of your experiences.

#5: Flushing, itching, or skin reactions

In MCAS, the release of chemicals such as histamine may cause flushing, itching, or hives.

Flushing is more typical with MCAS, but some people with POTS, particularly those who also have mast cell activation, report similar flushing episodes. These may be linked to changes in blood vessel response or sensitivity to temperature.

#6: Headaches and migraines

Headaches or migraines can occur in both MCAS and POTS.

In MCAS, chemical mediators (like histamine) may cause blood vessels to widen, which can contribute to headaches. In POTS, factors such as dehydration or changes in blood flow can increase headache risk.

{{pro-tip-1}}

Why do MCAS and POTS often coexist?

Experts are still studying both conditions to understand why they sometimes occur together. The exact cause isn’t clear, but several ideas may help to explain the overlap.

Immune system activation

Both conditions may involve changes in how the immune system communicates.

In MCAS, mast cells release inflammatory chemical mediators more easily. In POTS, inflammation and immune activity may affect how the nervous system controls heart rate and blood flow.

Connective tissue fragility

Some people with Ehlers-Danlos syndrome also experience MCAS or POTS. This is sometimes referred to as “the trifecta” or “triad” of conditions.

Because EDS affects connective tissue throughout the body, researchers are exploring whether it may contribute to some of the vascular and autonomic changes linked to both POTS and MCAS. This may help explain why the conditions sometimes overlap.

Autonomic nervous system dysfunction

Mast cells are located close to blood vessels and autonomic nerve pathways throughout the body. Researchers are studying whether interactions between mast cell activity and the autonomic nervous system may contribute to overlapping symptoms in MCAS and POTS.

{{inline-cta-1}}

Can my MCAS medications make my POTS worse? (and vice versa)

Some treatments for one condition may also influence the other.

For example, certain antihistamines, especially older types, may cause drowsiness or a drop in blood pressure, which could make dizziness from POTS feel worse.

On the other hand, older research from 2005 suggests beta-blockers, which are sometimes used for POTS, may affect mast cell activation pathways in people who are sensitive to this. However, the relationship is still not fully understood.

This doesn’t mean these medicines are unsafe. However, when MCAS and POTS overlap, it can sometimes be difficult to tell whether symptoms are coming from the condition itself, medication side effects, or changing triggers. This is why health tracking can be so helpful.

{{pro-tip-2}}

Diagnostic challenges: MCAS vs POTS

Because MCAS and POTS can share so many symptoms, getting an accurate diagnosis can take time. Both require specific testing and clinical observation. You may need to see several specialists before getting the answers you’re looking for.

How doctors diagnose POTS

POTS is often diagnosed using a tilt-table test or active stand (supine to standing) evaluations. These measure changes in heart rate and blood pressure when moving from lying down to standing. A sustained increase in heart rate (often 30 beats per minute or more) without a significant blood pressure drop supports a POTS diagnosis.

How doctors diagnose MCAS

Doctors diagnose MCAS by looking at patterns in your symptoms, lab results, and how your body responds to treatment over time.

They may order blood or urine tests looking for elevated mast cell mediators such as tryptase or histamine, although these levels are not always elevated outside of active flares. Doctors may also look at whether symptoms improve with antihistamines or other mast-cell-targeted treatments while ruling out other possible causes.

Why misdiagnosis happens

Many symptoms associated with MCAS and POTS, including fatigue, dizziness, palpitations, gastrointestinal symptoms, and brain fog, overlap with a wide range of other conditions.

Symptoms can also fluctuate significantly from day to day, which may make patterns harder to recognize or explain during short medical appointments.

In some cases, symptoms may initially be attributed to anxiety, stress, dehydration, or other more common explanations, particularly when standard test results appear normal between flares. This can be highly frustrating, especially when you know something feels wrong. It can also take time to connect symptoms that seem unrelated at first, particularly when they affect different parts of the body.

Keeping a consistent symptom log, including timing, triggers, medications, and flare patterns, can help healthcare providers identify recurring trends and better understand whether MCAS, POTS, or another overlapping condition may be involved.

How to manage MCAS and POTS

Managing MCAS and POTS together often means finding small, consistent habits that help stabilize the body’s responses. Because each person’s experience is unique, it’s best to work closely with a healthcare provider to tailor strategies and review medications regularly.

#1: Identify and track your triggers

Many triggers linked to MCAS and POTS can overlap.

Factors such as heat, dehydration, stress, illness, poor sleep, prolonged standing, certain foods, or overexertion may worsen symptoms in one or both conditions.

Because triggers and flare patterns can vary significantly from one person to another, tracking symptoms alongside daily factors such as meals, hydration, activity, medications, and temperature changes can help reveal patterns over time.

#2: Focus on hydration and electrolytes

People with POTS often benefit from increased fluids and electrolytes to help maintain blood volume, and those with MCAS may need to avoid drinks that trigger histamine release. Logging what you drink (and how you feel afterward) helps balance both needs safely.

See the best electrolyte options for POTS.

#3: Support the nervous system

Gentle movement, compression garments, and slow changes in posture can help improve circulation and reduce dizziness. Pairing these with relaxation techniques or pacing routines can help calm the body’s stress response.

#4: Optimize your environment and nutrition

Temperature changes, allergens, and certain foods may worsen symptoms for some people with MCAS.

For some people, a low-histamine diet, followed under the guidance of a healthcare professional or dietitian, can help you identify possible food-related symptom patterns.

#5: Collaborate and adjust regularly

Regularly review your symptom data with your medical team. Adjusting medications, routines, and supplements under medical guidance helps refine what works best for you.

Track your MCAS & POTS symptoms with the Human Health app

When you’re managing complex conditions like MCAS and POTS, small details matter. When symptoms appear, what triggers them, and how your body responds to your environment, medications, routines, or daily activities can all make a difference. But trying to remember all that information can feel overwhelming.

The Human Health app helps simplify this process. You can:

• Log daily symptoms, flares, and triggers in real time
• Track medications, hydration, and activity levels
• Share detailed PDF summaries with your healthcare team
• Manage multiple profiles if you’re tracking for a family member

By collecting your data in one place, you gain clearer insights into how your body reacts, and your doctor gets a more accurate picture to guide care decisions. You can start tracking your MCAS and POTS symptoms in the Human Health app today and share your personalized health summary at your next appointment. 

With consistent tracking, you’ll have the information you need for more informed, confident conversations with your healthcare provider.

Disclaimer: Human Health is a health tracking platform and does not provide medical advice, diagnosis, or treatment. The information in this guide is for educational purposes only and is not a substitute for professional medical care. Always consult your doctor or healthcare provider with questions about your health.

References

• Mast cell activation syndrome: An up-to-date review of literature (2024)
• Postural Orthostatic Tachycardia Syndrome, StatPearls (2023)
• Postural Tachycardia Syndrome (POTS), National Institute of Neurological Disorders and Stroke
• Association of postural orthostatic tachycardia syndrome, hypermobility spectrum disorders, and mast cell activation syndrome in young patients; prevalence, overlap and response to therapy depends on the definition (2025)
• Mast Cell Activation Syndrome and Gut Dysfunction: Diagnosis and Management (2024)
• Mast cell activation mediates blood-brain barrier impairment and cognitive dysfunction in septic mice in a histamine-dependent pathway. (2023)
• Hyperadrenergic postural tachycardia syndrome in mast cell activation disorders (2005)
• Testing, The Mast Cell Disease Society
• Mast cells in the autonomic nervous system and potential role in disorders with dysautonomia and neuroinflammation (2024)
• Mast Cell Activation Disorder and Postural Orthostatic Tachycardia Syndrome: A Clinical Association (2021)
• Postural Orthostatic Tachycardia Syndrome, Dysautonomia International
• ‍H1 Antihistamines: Current Status and Future Directions (2008)