MCAS, HISTAMINE INTOLErANCE, MYCTOTOXINS

Histamine intolerance, Mast Cell Activation Syndrome & Mycotoxicosis are subjects close to home for me. 

In Autumn of 2022 I began to experience symptoms I’d never had to deal with in my life before. These included marked facial swelling, rash, intolerance to chemical smells and perfumes and my face felt like it was on fire. This proceeded to sleep disturbance and I soon realised that I was having symptoms of histamine intolerance and an overactive immune system. 

I’m very thankful to Dr Becky Campbell for all of the great work she has done in relation to MCAS and I quickly made changes to adopt a low histamine diet as well as doing targeted testing. Testing revealed significant gut dysbiosis and inflammation and over the next 2 years my journey led me down the path of mycotoxins. 

Ultimately for me, as is the case for so many others who deal with MCAS, the root cause of my issues came down to mycotoxins. 

And that’s where it gets interesting. Because I’d been following a carnivore diet for several years at that point and typically animal foods are not the usual source of mycotoxins. Cereals tend to be the most likely culprit but I hadn’t eaten those for years. 

The only thing I had been consuming intermittently was coffee, and I was able to narrow down my exposure to an artisan coffee company – not even instant coffee (which I never drink, by the way)! And I wasn’t even having that much. It started as a single coffee each weekend day, but for various reasons drifted up to being a single coffee 4 or 5 days per week.

I was able to narrow it down to this as coffee krept back into my life in 2024 and so did some new-onset nerve pain – down one thigh and across both hands. The kind of pain that makes day-to-day functioning more of a challenge. 

Well, that and more facial swelling, rash, skin-on-fire, abdominal pain and so on…

I share this story because I know I wouldn’t have had any good answers about what was wrong with me from going down the conventional medical route. 

If I hadn’t done the testing I wouldn’t have known for sure that mycotoxins were my main issue. 

So where do they come from?

Because mycotoxins are mainly present in food and feed, the gut is the first target for mycotoxin toxicity, but it is also the site of the absorption of mycotoxins that leads to systemic exposure to these compounds.

Mycotoxins are bad news for gut health and anyone versed in root cause medicine knows how important gut health is. 70% of our immune system resides in the gut. So it’s no wonder symptoms of a dysregulated immune system pursue when you have a mycotoxin issue. 

Mycotoxins disrupt the intestinal wall – the epithelium and also eliminate beneficial bacteria in the microbiome and can pave the way for gut pathogens to take over.  

Symptoms can affect multiple bodily systems so are often confusing for clinicians not familiar with the illness – “the great masquerader”. 

There are different types of mycotoxin - some are carcinogenic, disrupt hormonal function, are toxic to the immune system, kidneys, liver, skin and brain. Study here. 

Upon ingestion of contaminated food or feed, the GI tract is particularly affected by mycotoxins. For example, mycotoxins can alter the normal intestinal functions such as barrier function and nutrient absorption. Some mycotoxins also affect the actual structure of the intestinal wall. 

Certain mycotoxins affect fertility and Ochratoxin A (OTA), which is the most common and relevant fungal toxin of the group has its main target as the kidney. Study here.

OTA ultimately leads to more oxidative stress in the body and can induce cell death as well as intestinal permeability. Study here.

Interestingly, recent studies showed OTA triggered autism via an epigenetic mechanism. Study here. 

Ultimately mycotoxins can have negative effects on the microbiome diversity and some studies have shown that OTA reduces beneficial microbes such as lactobacillus and bifidobacterium. Study here.

And what’s more is that many strains of probiotics possess the ability to reduce the level of mycotoxins, particularly via binding. 

Some strategies I personally found helpful for managing MCAS triggered by mycotoxins included the obvious: avoid the source of the mycotoxins in the first place – the fancy coffee!

A low histamine diet is all I could manage for a while. Kefir and probiotics for the gut support, binders and sauna to detox from the mycotoxins. Plus minerals to replace what might be lost via binders and sauna. 

It can be a long road to recover from MCAS but it’s most certainly worth it. The nerve pain improved within several weeks of using a detox protocol although ultimately it can take 6 – 12 months to really make a dent in the toxic load. 

And there can be neuropsychiatric symptoms due to mycotoxins, so if you suffer from persistent mental health symptoms that are being stubborn to other interventions, it is possible it could be a mycotoxin issue. Study here. 

The gut isn’t just a digestion machine—it’s a command centre for immune function, hormonal balance, and neurological health.

But this powerhouse can be under constant assault from a silent enemy: mycotoxins.

These toxic compounds—produced by moulds in our food supply—have a direct and damaging effect on the intestinal barrier, particularly a family of tight junction proteins called claudins.

And the consequences? Inflammation, immune dysregulation, cancer, and a rising tide of chronic disease.

Let’s break it down.

The intestinal barrier is your frontline defence system.

It’s made up of:

• A mucus layer rich in immune proteins.
   
• A tight epithelial wall sealed by proteins like claudins.
   
• A local immune army including dendritic cells and intraepithelial lymphocytes.
   

If this barrier breaks down, toxins, microbes and undigested food particles leak into the bloodstream.

This triggers systemic inflammation—a known root cause of autoimmune disease, metabolic dysfunction, mood disorders, and cancer.

Claudins are structural proteins that form tight junctions between intestinal cells.

They control what gets absorbed and what stays out.

Different claudins have different jobs:

• Pore-sealing claudins (like CLDN-1, CLDN-3, CLDN-4) keep the barrier tight.
   
• Pore-forming claudins (like CLDN-2, CLDN-15) allow selective passage of water and ions.
   

Disrupt the balance, and you create permeability, dysfunction, and disease.

Mycotoxins are fungal poisons found in contaminated cereals, nuts, dried fruit, coffee, beer, wine and even processed foods.

They’re not rare. They’re everywhere.

They’re resistant to heat, hard to remove, and dangerously under-regulated.

The worst offenders include:

• Aflatoxins (AFB1) – linked to liver cancer
   
• Fumonisins (FB1) – associated with esophageal cancer
   
• Zearalenone (ZEA) – mimics estrogen and disrupts reproduction
   
• Deoxynivalenol (DON) – causes vomiting and barrier dysfunction
   
• Patulin (PAT) – damages epithelial cells in the gut
   

Each mycotoxin targets the gut differently, but the pattern is clear:

• Aflatoxin B1 lowers claudin-1 and ZO-1, thins the gut lining, and disrupts nutrient absorption.
   
• Fumonisin B1 suppresses claudin-1/-4, occludin, and mucin genes—compromising both structure and microbiota.
   
• Zearalenone reduces claudin-4 and alters the gut flora; at low doses, it even stimulates cancer cell proliferation.
   
• Deoxynivalenol damages stem cells, reduces claudins, increases inflammatory cytokines, and hinders mucus repair.
   
• Patulin disorganises claudin structure and shreds the gut lining.
   

The result? A leaky, inflamed, immunologically chaotic gut.

Here’s the real kicker: we’re not exposed to one mycotoxin at a time.

Most food samples are contaminated with multiple mycotoxins, working synergistically to magnify damage.

Combined exposures (like AFB1 + OTA + ZEA) cause more harm than each compound individually.

And this is not theoretical—analysis of global food and feed samples shows that co-contamination is the rule, not the exception.

Emerging evidence shows mycotoxins don’t just irritate the gut—they may help initiate and promote cancer.

In GI cancers such as colorectal, gastric, liver, and esophageal cancers:

• Claudin expression is often dysregulated.
   
• Mycotoxins like DON and ZEA directly influence claudin levels and localisation.
   
• Some mycotoxins promote epithelial-to-mesenchymal transition (EMT), invasion, and metastasis.
   

This makes claudins a potential biomarker and therapeutic target in gut-derived cancers.

1. Stop underestimating foodborne toxins. Mycotoxins aren’t rare. They’re widespread. They’re dangerous. And they’re underreported.
    
2. Protect your gut barrier. This includes:
    
   • Supporting healthy mucus production (e.g. nutrient-dense diet)
      
   • Enhancing tight junction integrity (e.g. circadian rhythm alignment)
      
   • Reducing exposure to contaminated foods—especially conventional grains and poorly stored products.
     
      

Understand your own risk. If you struggle with autoimmune disease, IBD, infertility, fatigue, or food sensitivities, you may already be paying the price.
 

Your gut is under siege. Not just from antibiotics and stress—but from invisible, toxic fungal metabolites that breach your defences and alter your biology.

The science is clear: mycotoxins disrupt claudins, compromise the gut barrier, and contribute to chronic disease and cancer.

It’s time to stop ignoring this. It’s time to start protecting the gut like the vital organ it is.

Because if your gut barrier breaks down, everything breaks down.

Reference:

Kozieł, M.J.; Ziaja, M.; Piastowska-Ciesielska, A.W. (2021). Intestinal Barrier, Claudins and Mycotoxins. Toxins, 13(11), 758. https://doi.org/10.3390/toxins13110758