Mast Cell Activation Syndrome (MCAS): Causes, Symptoms + Steps To Improvement

Mast Cell Activation Syndrome (MCAS) is still a relatively new health condition, having only been listed as a medical diagnosis since 2016.

However, approximately 17% of the population suffer from MCAS. Plus, it’s extremely likely that this number is much higher due to undiagnosed cases.

What Is Mast Cell Activation Syndrome (MCAS)?

Mast cell activation syndrome (MCAS) involves a multitude of symptoms that arise primarily in the skin, gastrointestinal, cardiovascular, respiratory, and neurological systems. (1)

Mast Cell Activation Syndrome

What Are Mast Cells?

To help you understand more about mast cell activation syndrome, let’s first talk about mast cells and their job. Mast cells are immune cells located in tissues and organs throughout the body - including the sinuses, eyes, ears, bladder, skin, blood vessels, lymph, lungs and digestive tract.

They have many different receptors and more than 200 mediators. Hence the widespread bodily and brain symptoms that can occur as a result of mast cell activation syndrome.

Mast cells have receptors for mold, bacteria, viruses, candida, vitamin D and hormones to name a few.

Histamine is the best known mediator - with numerous roles, including being involved in inflammation and acting as a neurotransmitter.


Essentially, your mast cells act like the interface between your Immune system and your nervous system and their sensing response is exceptionally quick.


Your mast cells can communicate with your nerve endings in a number of ways. The first way is by releasing mediators, which may bind to receptors on the nerve cells.

The second way is by the mast cells themselves sticking to nerve cells through certain molecules, which allows them to send signals when their membranes are touching.

While mast cells play a hugely protective role in the body, problems start to occur when confusion sets in - about what is right and what is wrong and as a consequence they go ballistic over-responding to everything.

Because of their interaction with the nervous system, mast cell activation syndrome inevitably causes dysautonomia (dysfunction within the nervous system) which in itself can lead to a multitude of health and wellness issues.

Causes of MCAS

So, in mast cell activation syndrome, excessive amounts of inflammatory mediators are released in response to triggers such as foods, fragrances, stress, exercise, medications or temperature changes (2).

This inflammatory response can cause allergic reactions. For example, smelling laundry detergents or petrol fumes can trigger an anaphylaxis reaction in some people with MCAS. Reactions from anything that touches the skin is also possible, and of course reactions to food in the gut too.

Mast cells can also be activated by internal triggers like emotional or mental stress, mold toxicity, a virus, bacterial infection.

The Link Between Covid & MCAS

Studies suggest that theoretically, COVID-19 infection could lead to exaggeration of existing undiagnosed mast cell activation syndrome, or could activate normal mast cells owing to the persistence of viral particles (3).

This is one of the reasons why mast cell activation syndrome is being talked about so much in the functional health world right now.

On top of Covid, mold infections are on the rise, as well as increased mental and emotional stress, and increased environmental toxic burden. All of which create lots of unhealthy activity within the immune and nervous systems.

Any infection will activate mast cells but it doesn’t mean that everyone gets mast cell activation syndrome after the infection has been taken care of. In most cases the mast cells should reset. It’s the over-activation of the mast cells that creates secondary issues and MCAS.

What I’ve found with clients is there’s usually already a history of underlying MCAS pre the latest trigger, which then sends the mast cells into overdrive - worsening underlying symptoms and creating new issues.

So, the condition may be mild in some people and only exacerbate in response to a significant life stressor, which could be physical or psychological in nature (e.g. separation, house move, job change, travel, infection, exposure to infections, working or living in a water damaged building, exposure to cold or heat).

In others, symptoms may develop from a young age and slowly become worse over time. Because this condition is showing up in young people too.

Physical Manifestations

Connective tissue disorders can activate mast cells too - like POTS (Postural orthostatic tachycardia syndrome), CCI (Craniocervical Instability), EDS (Ehlers Danlos Syndrome) and even excess laxity and improperly formed connective tissue.

Histamine / MCAS

It can be confusing working out whether symptoms are related to Mast Cell Activation Syndrome (MCAS), or Histamine Intolerance (HI).

Histamine is just one of the 200 plus mediator chemicals released by mast cells, so if someone has MCAS it doesn’t mean to say that they have Histamine Intolerance too.

Most people with MCAS do have an exaggerated sensitivity to histamine, but not everyone who is histamine intolerant has MCAS.

Ultimately there is a root cause, or should I say “root causes” because MCAS is triggered by more than just one infection or one stressor. Focusing on addressing root causes are essential to overcoming MCAS.

How Can MCAS Impact Gut Health?

Given the widespread presence of mast cells throughout the digestive tract where the majority of our immune system lives, it makes sense that mast cell activation syndrome can impact our gut health too. And, vice versa poor gut health can trigger MCAS due to the intimate relationship between the gut and immune systems. Those with irritable bowel syndrome (IBS) are known to have more reactive mast cells.

Typically with MCAS changes in gut motility take place first whether this is a decrease or increase in bowel movements (4). This is due to the nervous system and its role in the whole digestive process from mouth to anus, plus as mentioned earlier the high level of interaction between mast cells and nerve cells.

Once bowel movements become disrupted inevitably it affects the mucosal barrier lining, and ultimately triggers or worsens gut microbiota dysbiosis and leaky gut.

MCAS Symptoms

Symptoms resulting from the inappropriate and excessive release of chemical mediators from mast cells are extremely diverse and varied, which adds to the mysterious nature of the disorder.

Those with MCAS will experience several symptoms. Here’s an exhaustive list of symptoms, but not everything:

  • Asthma, Anaphylaxis & Allergies
  • Bladder Irritability, Frequent Urination & Interstitial Cystitis
  • Fatigue
  • Food Intolerances
  • Gut symptoms - Diarrhoea, Bloating, Constipation, Heartburn, Abdominal Cramping, Nausea
  • Headaches, Brain Fog & Migraines
  • Joint, Muscle & Nerve Pain
  • Low Blood Pressure
  • Nasal stuffiness
  • Overreaction to chemical intolerances, bee stings & insect bites
  • Poor wound healing and easy bruising
  • Skin Problems - Eczema, Facial Flushing, Hives, Psoriasis, Itchiness, Burning Feeling
  • Tachycardia (fast heart rate)

Improving MCAS Symptoms

Taking a holistic approach to MCAS is key.

1. Identify + Remove Triggers & Toxins

In the first instance it's important to is to identify and avoid the specific triggers. This can take time. But as a person’s symptoms improve, tolerance for these triggers may also improve.

One of the biggest environmental triggers of MCAS is mold. When it comes to MCAS and mold it’s vital to eliminate the source of the toxin and this means removing yourself from any moldy buildings.

Various microbes including mycotoxins (mold toxins) can disrupt the immune system and cause mast cells to go haywire. Once you’ve removed the source you can treat the mycotoxins in the body and brain.

2. Reduce Stress

Stress reduction is crucial in stabilising mast cells. When you’re stressed, your body releases corticotropin-releasing hormone (CRH), which is associated with the activation of skin mast cells (5).

Incorporate stress reducing activities into your daily life e.g. breathing exercises, meditation and other relaxing and soothing techniques to help calm the mast cells and induce a sense of safety within the body.

3. Adopt a Healthy Routine

Establishing a healthy routine is a fantastic way to help stabilise your mast cells, because just like your gut microbes mast cells exhibit circadian rhythm patterns.

Aim to wake up and go to sleep at the same time.

Sleeping can be tricky with MCAS as symptoms tend to rear their ugly head more at night. So, do everything you can to promote a good night’s sleep during the day by getting enough natural light. This will support increased melatonin (sleep hormone) production and set you up for optimal sleep quality.

4. Diet & Supplements

A low histamine diet can be beneficial to manage symptoms in the first instance, if histamine is an issue.

Not everyone responds to a low histamine diet and potentially low oxalate and low lectin diets can also be helpful, but it’s important to work with a health expert to navigate the complexities of MCAS so that you don't create more problems.

There’s lots of natural supplements that can be very helpful for MCAS. Again it’s a question of finding the ones that suit the individual, their symptoms and their genetic make-up.

Most times people with MCAS are extremely sensitive to drugs and supplements, so it’s important not to throw a ton of stuff at the body all at once. Slow and steady is the best way to make any progress with MCAS.


Let me know in the comments below if you found this post helpful. Do you think you have MCAS? And what have you tried for treatment of MCAS in the past? 

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Meet Nicola - blog posts

Meet Nicola

Hello, I'm a Holistic Nutritionist, Certified Functional Medicine Practitioner, Breathwork Instructor and Pain & Stress Management Therapist with heaps of experience of helping others tweak and transform their health and life. 

Let's work together to optimise how you look, feel and function for better health and wellness.

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