Histamine Intolerance vs. MCAS: What’s the difference & how to find relief

Ever felt like your body is overreacting to things that seem totally harmless—like certain foods, smells, or even changes in temperature? You might have heard of histamine intolerance or mast cell activation syndrome (MCAS). While these two conditions can seem similar, they’re actually quite different under the surface.

Understanding which one you’re dealing with can make all the difference in finding the right path to relief.

What Is Histamine?

Histamine is a natural chemical released by mast cells—the first line of defence in your immune system. These cells hang out mostly along your body’s “front lines” like your gut lining, skin, and respiratory tract, where they help protect you from invaders.

But sometimes, often due to over-stimulation or infection, these cells can become confused.

When things go wrong: MCAS vs. Histamine Intolerance

MCAS (Mast Cell Activation Syndrome)

In MCAS, your mast cells become hyper-reactive. They start sounding the alarm (aka releasing histamine) in response to everyday things like food, smells, heat, or even exercise. This overreaction is often triggered by long-term exposure to things like mould, environmental toxins, chronic infections, or nutrient deficiencies.

Key signs of MCAS:

Reactions happen FAST—within 30 seconds to 30 minutes of exposure.
Affects multiple systems at once (e.g. brain fog and gut issues).
High sensitivity to supplements, chemicals, light, sound, etc.
Often develops after long-term stress on the body (gut issues, methylation problems, chronic inflammation).
Can take time to untangle and requires detailed, whole-body support.

Histamine Intolerance

This is more about your body’s inability to break down histamine properly. You might be eating a diet high in histamine (think aged cheese, wine, or leftovers), or your body might not be producing enough of the enzymes needed to break it down.

There are two key enzymes:

DAO (made in the gut) – handles dietary histamine.
HNMT – breaks down histamine in other parts of the body.

Gut inflammation, poor digestion, or lacking nutrients can impair these enzymes, leading to a histamine build-up.

Key signs of histamine intolerance:

Symptoms show up later, often 30+ minutes after a trigger.
Less likely to react to chemicals or supplements.
Often improves with a low-histamine diet and DAO supplements.
Usually stabilises in 1–2 weeks with proper support.
Threshold-based—symptoms occur once histamine builds up beyond what your body can handle.

Common symptoms to watch for

Whether it’s MCAS or histamine intolerance, symptoms can overlap. Here are some of the most common ones:

Fatigue
Brain fog
Anxiety or mood changes
Skin rashes, hives, redness
Asthma or shortness of breath
Digestive issues (bloating, nausea)
Sinus congestion or runny nose
Insomnia
Itching or swelling

MCAS-specific symptoms may also include:

Sensitivity to light/sound
Chemical sensitivities
Chronic infections

💡 What You Can Do About It

1. Support Your Gut

The gut is where histamine processing starts. Reduce inflammation and support digestion to improve DAO enzyme function.

Consider gut-healing diets (low FODMAP, anti-inflammatory)
Look at probiotics (be cautious—some strains increase histamine!)
Support stomach acid and enzyme production

2. Check Your Nutrient Levels

DAO and HNMT need key nutrients to work well:

Zinc, Vitamin C, Vitamin B6, Copper, SAMe (supports methylation), Magnesium (nervous system support)

3. Balance Your Hormones

For women, histamine issues often spike mid-cycle due to rising oestrogen, which activates mast cells and suppresses DAO. Meanwhile, progesterone (produced after ovulation) helps calm things down.

Tips:

Track your cycle and symptoms
Support ovulation naturally (with nutrition, stress management)
Help your body clear excess oestrogen

4. Calm Your Nervous System

A chronically stressed or overstimulated nervous system can trigger mast cell activation. This is known as the cell danger response.

Supporting the vagus nerve can help:

Deep breathing, cold exposure, singing, humming, gargling, meditation and nervous system regulation tools

For MCAS especially, this is often the best place to start.

🧪 How can we help?

If you suspect histamine intolerance or MCAS, working with a practitioner who understands these conditions is key. Functional testing can assess DAO enzyme levels, nutrient panels, genetic testing (for enzyme function or methylation), gut testing for inflammation, infections, or dysbiosis

🧘‍♀️ You can feel better

Whether you're dealing with histamine intolerance or MCAS, know that healing is possible. It starts with understanding your body, reducing your histamine load, and gently rebuilding balance across your gut, hormones, and nervous system.

The key? Patience, consistency, and the right kind of support.

Book a free call with us here today.