Understanding Mast Cell Activation Syndrome (MCAS): What It Is and What Causes It

Do you suffer from unexplained skin rashes, itching, brain fog, food sensitivities, or sudden anxiety — and no one seems to know why? You might be dealing with a lesser-known but increasingly common condition called Mast Cell Activation Syndrome (MCAS).

MCAS is a chronic condition where the body’s mast cells — a type of immune cell — become overly reactive, releasing histamine and other inflammatory mediators in response to triggers that shouldn’t normally cause a reaction. The result? A wide range of symptoms that can affect nearly every system in the body.

Let’s explore what MCAS is, how it shows up, and most importantly — the underlying root causes that may be driving it.

What Are Mast Cells?

Mast cells are immune sentinels that live in tissues throughout the body — especially the skin, lungs, gut, sinuses, and brain. When they sense a threat, such as an infection or allergen, they release histamine, cytokines, and other chemical messengers to protect you.

But in MCAS, these mast cells misfire — reacting to harmless stimuli like food, heat, smells, or even stress. Over time, this can lead to chronic inflammation, immune dysregulation, and nervous system hypersensitivity.

Common Symptoms of MCAS

MCAS symptoms are often misdiagnosed because they can mimic other conditions. Some of the most common include:

• Skin: rashes, hives, eczema, itching, flushing

• Gut: bloating, diarrhea, nausea, food intolerances

• Lungs: shortness of breath, asthma-like symptoms

• Brain: brain fog, anxiety, insomnia, irritability

• Cardio: palpitations, lightheadedness, POTS-like symptoms

• Reproductive: painful or irregular cycles, PMS, estrogen sensitivity

What Causes MCAS?

In functional medicine, we don’t just suppress symptoms — we ask why they’re happening. Below are some of the most common root causes and triggers that drive mast cell dysregulation:

1. Chronic Infections

Tick-borne illnesses like Lyme disease, co-infections like Bartonella and Babesia, or reactivated viruses like EBV can keep your immune system in a chronically inflamed state, making mast cells hyper-reactive.

2. Mold and Mycotoxins

Toxic mold exposure is one of the most common overlooked drivers of MCAS. Mycotoxins can directly activate mast cells, damage detox pathways, and trigger systemic inflammation — especially in genetically sensitive individuals.

3. Gut Imbalances and Leaky Gut

Your gut is home to 70% of your immune system. When dysbiosis (imbalance in gut bacteria) or intestinal permeability (“leaky gut”) is present, food particles and toxins can leak into the bloodstream, triggering immune responses and mast cell activation.

4. Environmental Triggers

Fragrances, cleaning chemicals, EMF exposure, smoke, and pollutants can all overwhelm the body’s detox system and sensitize mast cells, especially in people with a lower threshold due to nutrient deficiencies or chronic inflammation.

5. Nutrient Deficiencies

Key nutrients like vitamin C, quercetin, zinc, B6, and magnesium play critical roles in mast cell stability and histamine breakdown. When these are depleted (often due to stress or poor absorption), the body is more prone to exaggerated responses.

6. Hormonal Imbalances

Women often notice worsening MCAS symptoms around ovulation or before their period. That’s because estrogen can increase mast cell reactivity, especially in the presence of low progesterone or adrenal fatigue.

7. Nervous System Dysregulation (Vagus Nerve / Limbic Loop)

Your nervous system and immune system are deeply connected. Chronic stress, trauma, or dysregulated vagus nerve signaling can create a feedback loop that keeps mast cells constantly on high alert, even in the absence of a real threat.

What You Can Do

The good news? MCAS can often be managed or even reversed when we address the root causes and support the body’s natural ability to heal.

Functional medicine approaches typically include:

• Low-histamine, anti-inflammatory diet

• Natural mast cell stabilizers like quercetin, vitamin C, DAO enzymes

• Binders and detox support (especially if mold is involved)

• Nervous system regulation through breath work, vagal tone exercises, or limbic retraining

• Treating underlying infections or gut imbalances

• Lifestyle changes to reduce exposures and support healing

Ready to Get to the Root?

If you suspect MCAS may be affecting your health, you don’t have to suffer in silence. At Your Functional Health, we specialize in uncovering hidden triggers like mold, gut imbalances, and chronic inflammation — and creating personalized protocols to help you heal.

Book your functional medicine consult with Xenia today and take the first step toward calm, clear, symptom-free living. Serving Austin, Houston, Dallas, San Antonio and the entire State of Texas.

Your Functional Med NP,

Xenia