Is It MCAS? Understanding Histamine, Flare Triggers & Immune Reactivity with Dr. Jill Carnahan

In this episode of the Autoimmune RESET Podcast, I’m joined by Dr Jill Carnahan, MD — functional medicine physician, author of Unexpected, and someone whose clinical work is deeply shaped by her own lived experience of chronic illness.

Jill shares her extraordinary personal journey, from growing up on a farm with heavy chemical exposure, to being diagnosed with aggressive breast cancer at just 25, followed by Crohn’s disease, Hashimoto’s thyroiditis, and later mould-related illness. Rather than accepting these diagnoses as isolated events, Jill’s curiosity led her to ask the deeper question so many people with autoimmune disease eventually ask: why?

From there, we explore one of the most complex and misunderstood areas in modern medicine — mast cell activation syndrome (MCAS). Jill explains how mast cell activation is often not a primary diagnosis, but a downstream expression of deeper immune overload, driven by a combination of genetic susceptibility, infectious burden, toxic exposure, gut permeability, and nervous system stress.

We discuss why MCAS is frequently missed or poorly understood in conventional medicine, what a true diagnosis involves, and why testing can be challenging and unreliable if not handled correctly. Jill also shares why attempting detoxification or antimicrobial treatment before stabilising mast cells can make symptoms dramatically worse — something many listeners may recognise from their own experience.

This conversation goes beyond theory and testing. Jill walks through her clinical approach to stabilising mast cells, including where natural supports, medications, limbic system regulation, trauma work, and lifestyle foundations fit into the healing process. We also talk honestly about overwhelm — how to reduce toxic load gradually, without fear or perfectionism, and why “clean air, clean water, clean food” remain non-negotiables for immune health.

Finally, Jill offers something many people need to hear: hope. Despite decades of immune and inflammatory illness, she now lives a full, active life — travelling, working, and thriving — and shares the daily practices that support her resilience, from sleep and nature to nervous system regulation and connection.

This episode is essential listening if you:

• Suspect MCAS or histamine intolerance
• Have worsened after infections, COVID, mould, or detox protocols
• Feel reactive to foods, environments, or supplements
• Want a root-cause, compassionate understanding of immune dysregulation
• Need reassurance that recovery is possible, even when things feel complex

A deeply validating and educational conversation for anyone navigating autoimmunity, chronic illness, or unexplained immune reactivity.

🔗 Dr Jill Carnahan – Official Website
Find her clinical work, blogs, resources, podcast and more here: https://www.jillcarnahan.com/

🎬 Doctor/Patient — Documentary Film
Watch or learn more about the documentary featuring Dr Jill’s health journey and chronic illness insights: https://doctorpatientmovie.com/

📘 Jill’s Book — Unexpected
Explore her memoir Unexpected: Finding Resilience Through Functional Medicine, Science, and Faith via her website (linked above). 

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