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Mast Cell Activation Syndrome



Mast cells are cells of the immune system. They are the key players in the bodys' reaction to a threat - virus, bacteria, fungi. When activated they can kill by "engulfing" - literally eating the threat.

When stimulated mast cells also undergo a process called degranulation when they rapidly release the inflammatory mediators stored within them - histamine, cytokines, leukotrienes.

Mast cells are designed to protect us from these pathogenic threats and so are strategically located in areas of the body that most frequently come into contact with the external environment. They live in the connective tissue and are found mainly in the skin, gut, blood vessels and lungs.

When they release their inflammatory mediators they kick start the immune response by:


  • Activating and recruiting other immune cells to target and eliminate the invader

  • Increasing vascular permeability to allow other immune cells to get where they are needed

  • Inducing vasodilation to allow other immune cells to arrive quicker

  • Stimulating lung and smooth muscle contraction

The mast cells have a rapid effect and also a long term inflammatory response. Mast cells are known to be activated by SARS-CoV-2. In the acute covid infection there is a hyper inflammatory reaction . There is the rapid production and hyper activation of T cells, macrophages, natural killer cells, cytokines and mast cells; all the virus fighting cells. The mast cells recognise viral products and help orchestrate the functions of the other immune cells. BUT the mast cells also have the special receptors on their surface (ACE 2 receptors) and the SARS-CoV-2 sneakily uses these to get into our cells and wreak havoc.

Mast cells promote thrombosis- blood thickening and clotting (pulmonary embolism and strokes)


Those surviving the hyper inflammatory reaction of an acute Covid-19 infection may go on to having chronic multi system illness.

The mystery is still why those with mild, moderate or even asymptomatic covid infection also go onto have chronic illness.

It could be that we have developed, or always had a disorder, called Mast Cell Activation Syndrome or MCAS. In mast cell activation syndrome, you have a normal amount of mast cells floating around in your body, but they malfunction.


Mast cell activation syndrome occurs when your mast cells overreact, releasing too many inflammatory mediators too frequently. This inappropriate and exaggerated response causes your immune system to essentially go haywire.

MCAS is a chronic multi system disorder with inflammatory and allergic themes. A flare can bring on any of the following:

GUT - increases fluid secretion and muscle contraction leading to vomiting, diarrhoea, bloating, abdominal cramping, irritable bowel syndrome ( IBS) and also NEW allergies

LUNG - triggers construction of the airways, wheezing, breathlessness, congestion, dry coughing, asthma like symptoms, and increased mucous production

SKIN - swelling, itching, flushing, hives, rashes, eczema.

HEART - low blood pressure, rapid heart rate, palpitations, fainting

BRAIN - headache, dizziness, confusion, poor concentration, brain fog, fatigue and insomnia

These symptoms sound very familiar to anyone who has Long Covid relapses and those with Post Covid Positional Orthostatic Tachycardia Syndrome.


Patients with MCAS are often undiagnosed and untreated. They would normally describe themselves as healthy people prior to infection. They have dysfunctional mast cells which when challenged by a virus such as Covid react uncontrollably. It has been hypothesised that our mast cells may have been under partial control during the acute Covid infection but the MCAS has put us at increased risk of developing post infectious illness or #longcovid.


The triggers for a MCAS flare are huge:

Environmental: Sun exposure, sudden temperature or altitude changes, mold, dust, pollen, animal dander, heavy metals, pollution.

Noxious smells: Perfumes, smog, exhaust, synthetic fragrances, cleaning supplies.

Certain medications: Narcotics, antibiotics, NSAIDs, anaesthetics, opioids, muscle relaxers, some supplements, contrast dyes used in medical imaging.

Physical stimulation: Pain, trauma, exercise, friction and vibration, fatigue.

Hormonal changes: Oestrogen and progesterone shifts such as during a woman’s menstrual cycle.


High histamine foods and beverages: Fermented foods, alcoholic beverages, aged meat and cheese, nuts, certain fruits and vegetables

Infection: Virus, bacteria, fungi, parasites.


Those who have developed new allergies after Covid especially ones with an anaphylactic reaction are likely to get tested for MCAS. For a diagnosis you need to have several symptoms- eg itching, hives, headache, gastrointestinal upset, low blood pressure- in 2 or more organs at the same time and it must reoccur. The blood is tested during an episode for tryptase and this must be higher than the patient’s baseline ( when they are not having an episode) They must respond to antihistamine medication. Note that these people must discuss a possible anaphylactic response to the new Covid-19 vaccination especially if they have been issued with a epinephrine auto injector.

So where does that the rest of us? MCAS has acute flares and this may explain our Covid relapses. We can lessen these by:


  • Following a low histamine diet- histamine this is one of the substances that mast cells released and can cause an acute and chronic inflammatory reaction. It’s a tough diet but it may help you get on top of the relapses, skin rashes, diarrhoea, reflux, cough, palpitations and brain fog.


  • Taking regular over the counter antihistamines or use the supplement DAO


  • Taking Quercetin - a key flavonoid that helps stabilize mast cells (see my blog/ instagram post for more on this)


  • Taking Bromelain - has been proven to help maintain a healthy cytokine balance and enhance your immune function.


  • Eating a diet rich in polyphenolic flavonoids - naturally occurring molecules found in apples, onions, dark chocolate, and red cabbage.


More information can be found at @histaminehangover, jillcarnaham.com. Dr Tina Peers who runs a menopause clinic is currently looking at MCAS and it's link to Long Covid with the help of the @peoplewith app.

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