Mast cell activation syndrome

Mast cell activation syndrome (MCAS) is a syndrome – a collection of signs and symptoms that fit together – characterised by non-specific inflammatory symptoms. This release of mediators can impact the reproductive and urinary tract, causing unpleasant or painful symptoms.

It’s important to note that MCAS can affect any part of the body, and everyone presents a little differently. If you suspect MCAS, talk to a practitioner experienced in treating and managing this condition.

How MCAS affects the urogenital tract

Some common issues that could be related to mast cell activation include interstitial cystitis or vulvodynia.

Urinary tract symptoms

  • Frequency of urination
  • Difficulty starting urination
  • Incomplete bladder emptying
  • Painful urination
  • Flank or abdominal pain from kidney stones
  • Blood in the urine (rare)
  • Signs of infection but test comes back clear

Vaginal/reproductive tract symptoms

Luteinising hormone activates mast cells, which then go on to release histamine to stimulate ovarian contractility, ovulation, and progesterone released by follicles. Antihistamines can thus prevent ovulation.

Mast cells are abundant in endometrial lesions, while in normal endometrium, mast cells are not activated. The tissue and fluids around endometrial lesions have inflammatory mast cell mediators present.

Pregnancy symptoms

  • Decreased libido
  • Infertility
  • Early miscarriage
  • Severe, excessive or prolonged vomiting
  • Pre-eclampsia
  • Pre-term labour
  • Poor response to anaesthetics

Hormonal symptoms

  • Delayed or premature puberty
  • Extremely painful periods
  • Irregular periods
  • Heavy periods
  • Weak bones
  • Thyroid abnormalities
  • High cholesterol or triglycerides
  • Blood sugar dysregulation, type II diabetes, hypoglycaemia
  • Issues transporting nutrients

MCAS and vulvodynia

In vulvodynia, there appears to be a disruption to the regulation of the inflammatory response as it relates to activation of the hypothalamic-pituitary (HPA) axis.

Biopsies show that vulvodynia sufferers have increased mast cell degranulation and infiltration compared with controls. Mast cell mediator, heparanase, was identified specifically in the vestibule of vylvodynia patients.

In the vestibule, heparanase degrades a component of basement membranes, heparin sulfate, and extracellular matrix for leukocyte infiltration.

Mast cell activation is increased in those with postmenopausal vulvodynia, when compared with premenopausal subjects, despite oestrogen receptor α and neural hyperplasia being about even in the two groups. The discrepancy suggests that further regulatory processes may contribute to the age-related incongruence.

Mast cell activation releases preformed mediators and cause the synthesis and release of other active molecules involved in inflammation, such as cytokines, eicosanoids and chemokines. After stimulation, mast cells produce proinflammatory cytokines and tumour necrosis factor-α, as found in vulvodynia biopsy samples.

MCAS and interstitial cystitis

Mast cells set off inflammation that causes pain. Interstitial cystitis (IC) is a bladder condition resulting in severe pelvic pain that has no known cause, and without consistent inflammation. IC symptoms correlate with elevated mast cell counts.

The cause of symptoms

The symptoms are caused by the inappropriate release of mast cell-produced compounds, but when there is no identified excess of mast cells (mastocytosis).

MCAS appears as unexplainable, chronic multi-system multi-symptom health problems. These health problems can start to make themselves known in infancy, childhood, adolescence or later after a trigger event such as a tick bite resulting in Lyme disease or an infection.

What is a mast cell?

A mast cell is an immune cell found in all human tissue, but are more concentrated in the skin and mucous membranes. Mast cells hold special mediators, such as histamine, tryptase, synthesised chemokines and cytokines, which are released when activated by the immune system. One main mediator is immunoglobulin E (IgE). If you’ve ever had an allergy test, this is a mediator that is tested for.

Non-immune triggers for mast cells to secrete these mediators include stress and chronic pain.

Mast cell activation causes the mast cell to burst, known as degranulation, and it releases its contents. It’s this process of degranulation that is responsible for a variety of reactive, allergic or inflammatory symptoms. The mediators stored inside the mast cell vary widely depending on the location in organs and tissue (where the cell ‘belongs’ n the body), thus when the mast cell bursts, what reaction occurs will depend on where the cell lives.

The mediators have different impacts, interacting with receptors in the tissue. The tissue affected is just about everything, including the nervous system, cardiovascular system, skin, respiratory tract, uterus, digestive tract, bone marrow and white blood cells. Meaning, any part of you could be affected by mast cell activation.

Mast cells may be activated selectively or non-selectively. Non-selective activation of a mast cell means the whole cell is degranulated, while selective activation results in the release of patterns of mediators, known as differential degranulation.

Mast cell activation syndrome is difficult to identify, with the diagnosis made from identifying the pattern of symptoms and case history. The patterns tend to escalate in severity after stress, for example, puberty, trauma and infections.

MCAS is a mast cell activation disorder (MCAD), with other conditions identified including cutaneous (skin) and systemic (whole-body) mastocytosis (mast cell proliferation).

Systemic mastocytosis (an excess of mast cells) is reasonably rare, occurring in one in every 364,000 people. MCAS is much more common, occurring in 5-10 per cent of the population. MCAS means overactive or sensitive mast cells.

MCAS tends to be familial, with 75 per cent of diagnosed people having a close relative also diagnosed. About half of those diagnosed with MCAS have children who are affected to varying degrees.

How to identify MCAS

The most common signs and symptoms of MCAS include:

  • Abdominal pain 48%
  • Alternating diarrhoea and constipation 36%
  • Anxiety/panic 16%
  • Asthma 15%
  • Chills 56%
  • Cognitive dysfunction 49%
  • Constipation 14%
  • Cough 16%
  • Depression 13%
  • Diarrhoea 27%
  • Difficulty swallowing 35%
  • Dizziness/fainting 71%
  • Easy bleeding/ bruising 39%
  • Environmental allergies 40%
  • Eye irritation 53%
  • Fatigue 83%
  • Fever 40%
  • Fibromyalgia symptoms 75%
  • Flushing 31%
  • Frequent infections 27%
  • Gastroesophageal reflux 50%
  • Hair loss 15%
  • Headache 63%
  • Heart palpitations/dysrhythmia 47%
  • Heat and cold intolerance 13%
  • Insomnia 35%
  • Itching/rash 63%
  • Multiple/odd drug reactions 16%
  • Nail changes 13%
  • Nausea and vomiting 57%
  • Non-angina chest pain 40%
  • Oral irritation/sores 30%
  • Period pain 16%
  • Poor wound healing 23%
  • Rashes 49%
  • Sinusitis 17%
  • Shortness of breath/laboured breathing 53%
  • Sweats 47%
  • Swelling that moves around the body 56%
  • Swollen lymph nodes 28%
  • Tingling/prickling skin 58%
  • Throat irritation 48%
  • Tooth/gum/dental deterioration 17%
  • Tremor 13%
  • Urinary symptoms (excluding interstitial cystitis) 27%
  • Visual anomalies 30%
  • Weight gain/obesity 17%
  • Weight loss 16%

Most common physical findings in MCAS

  • Abdominal pain (any location, any type, any severity) 32%
  • Achy/pained appearance 28%
  • Anxious demeanour 11%
  • Back tenderness (one or more points) 11%
  • Brain fog 12%
  • Bruising 22%
  • Cardiac murmur 11%
  • Chronically ill appearance 42%
  • Dental deterioration 21%
  • Depressed demeanour 11%
  • Dermatographism 76%
  • Epigastric tenderness (just below ribs) 19%
  • Flushing 12%
  • Mild diastolic hypertension (90-199 mm/Hg) 14%
  • Mild systolic hypertension (140-159 mm/Hg) 32%
  • Moderate systolic hypertension (160-179 mm/Hg) 12%
  • Obesity 37%
  • Pallor (paleness) 13%
  • Rash (any type) 34%
  • Right lower abdominal tenderness 19%
  • Right upper abdominal tenderness 15%
  • Soft tissue tenderness 16%
  • Swelling 39%
  • Tachycardia (fast heartbeat) 28%
  • Tingling/prickling 20%
  • Tired appearance 46%
  • Use of mobility-assisting devices 12%
  • Weakness 12%

Other conditions often found with MCAS include:

  • Gastroesophageal reflux disease (GORD or GERD) 35%
  • Hypothyroidism (underactive thyroid gland) 17%
  • Blood clots 13%
  • High blood pressure 29%
  • Headaches 17%
  • Frequent or atypical infections 13%
  • Multiple/atypical drug reactions 23%
  • Depression 16%
  • Obesity 13%
  • Abdominal pain 22%
  • Sinusitis 16%
  • Osteoarthritis 13%
  • Hysterectomy 21%
  • Fibromyalgia 16%
  • Anxiety or panic 12%
  • Hyperlipidaemia 20%
  • Anaemia of chronic inflammation 15%
  • Cardiovascular malformations 12%
  • Cholecystectomy 20%
  • Sleep apnoea 15%
  • Dermatitides (inflammatory skin conditions) 11%
  • Environmental allergies 19%
  • Frequent upper respiratory tract infections 15%
  • Pre-syncope or syncope 11%
  • Tobacco abuse 18%
  • Miscarriage 15%
  • Interstitial cystitis 11%
  • Asthma 18%
  • Pharyngitis of tonsillitis 14%
  • Chronic kidney disease 10%
  • Type 2 Diabetes 17%
  • Dysmenorrhea 14%
  • Postural orthostatic tachycardia syndrome (POTS) 10%

Diagnosis of MCAS

You may be diagnosed with a mixture of personal health history information and one or more of the following:

  • Functional testing for evidence of mast cell activation – urinary N-methyl histamine (a practical and stable marker), tested when symptoms are present
  • Plasma histamine and plasma heparin (though N-methyl histamine tends to provide greater accuracy)
  • A 24-hour urinary histamine metabolites of prostaglandin D2 (PGD2) or its metabolite may be supportive of a MCAS diagnosis

What drives MCAS?

There are several key drivers for MCAS:

  • Chronic stress
  • Gut dysbiosis and intestinal permeability (‘leaky gut’)
  • Sleep problems and insomnia
  • Chronic infections and chronic inflammatory response syndrome
  • Chronic pain
  • Oestrogen activity/exogenous oestrogen exposure

How chronic stress drives MCAS

Mental, emotional, metabolic, traumatic or physical stress may trigger the body’s innate stress response. In turn, the hypothalamus releases corticotropin-releasing hormone (CRH). CRH then stimulates the pituitary to release adrenocorticotropic hormone (ACTH), which in turn stimulates the adrenal glands to produce the stress hormone cortisol.

CRH causes the synthesis and release of mast cell mediators such as tumour necrosis factor-alpha (TNFα), proteases, tryptase, chymase, histamine, leukotrienes (LTs) and PGD2 from mast cells.

Over time, this response may result in the perpetual cycle of chronic mast cell activation and CRH activity.

How gut dysbiosis and intestinal permeability drive MCAS

Gut dysbiosis is the state whereby the digestive tract flora has become unbalanced. Intestinal permeability is the state whereby the intestine has become prone to letting much larger particles through than it should, also known as leaky gut. This leakage can cause an immune response.

Gut dysbiosis and intestinal permeability can contribute to MCAS via inflammatory compounds stimulating mast cell activation by aggravating toll-like receptors found on mast cells.

Having an imbalanced gut microbiome may mean the enzyme in the gut that metabolises dietary histamine may be lacking. Histamine therefore may continue to circulate, exacerbating mast cell activation.

Short-chain fatty acids produced by some gut bacteria may reduce the expression of genes associated with mast cell activation, the inflammatory response, and cytokine signally, thus reducing the frequency of MCAS symptoms. Dysbiosis may reduce colonies of such bacteria.

In instances where the intestinal barrier is performing loosely, antigens may enter the mucosa, causing mucosal mast cell activation, an inflammatory response, and altered mast cell-enteric nerve interaction.

How sleep disturbances and insomnia drive MCAS

Melatonin, the hormone that regulates our sleep-wake cycle (circadian rhythm), is directly prevents mast cell degranulation, infiltration and activation. When production of melatonin is interrupted, MCAS symptoms can occur.

How chronic infection or CIRS drive MCAS

Pathogenic bacteria, fungi and viruses produce toxins and proteins, which can active mast cells through pattern recognition receptors on mast cell surfaces resulting in Chronic Inflammatory Response Syndrome (CIRS). Receptors recognise and respond to molecular patterns produced by pathogens.

Some specific pathogens are known to activate mast cell receptors:

  • Staphylococcus aureus
  • Escherichia coli
  • Cholera
  • Pertussis
  • Clostridium difficile
  • Mycoplasma
  • Respiratory syncytial virus (RSV)
  • Rhinovirus
  • Reovirus
  • Dengue fever virus
  • Human immunodeficiency virus (HIV)
  • Influenza
  • Candida albicans
  • Cryptococcus neoformans
  • Aspergillus fumigatus

How chronic pain drives MCAS

Pain receptors, when activated by inflammatory mast cell mediators, may activate the release of pain signalling neuropeptides, which inturn can stimulate mast cell activation.

Once activated, this can cause a positive feedback loop resulting in ongoing mast cell activation and inflammation that may perpetuate chronic pain.

How oestrogen activity drives MCAS

Oestrogen, both human and exogenous (external/environmental), has been linked with mast cell activation. Oestrogen can bind to oestrogen receptors on mast cells and cause mast cell degranulation.

Mast cells express oestrogen receptors in the upper respiratory tract cells and interstitial bladder epithelium. Mast cell overactivation in these cells may be associated with increased oestrogen levels.

In oestrogen-driven conditions, for example, endometriosis, more oestrogen concentrations were associated with greater mast cell activity in ovarian endometriomas and period pain severity.

Treatment for MCAS

Non-drug treatments include:

  • Probiotics Lactobacillus paracasei and Lactobacillus rhamnosus to improve immune function and moderate overactivity (induces T regulatory cell production, dampens inflammation in immune disorders.
  • Quercetin – stabilises mast cells and basophils, reduces degranulation and histamine release.
  • Aller-7 – a patented blend of herbs that has antihistamine, antioxidant and anti-inflammatory activity, stabilises mast cells, down-regulates histamine release.
  • Fish oils high in omega-3 fatty acids – control underlying inflammation, support immune regulation, enhance clearance of pathogens. Encourages switch of proinflammatory M1 macrophages to anti-inflammatory M2 macrophages. Promotes tissue repair.
  • Prebiotics and fibre – promotes intestinal integrity, enhances microbiome composition, enriches commensal species associated with short-chain fatty acid production (especially butyrate, associated with moderating mast cell over-activity). Stimulates mucin secretion.
  • Herbal medicine for stress management and treatment of infections.
  • Low histamine diet to reduce intake of histamine-containing foods.

Pharmaceutical treatments include:

  • Epinephrine – used for acute anaphylaxis/allergic reactions.
  • Cromolyn sodium – typical dose is 200mg four times daily to reduce bone pain, abdominal cramping, diarrhoea, headaches and skin symptoms (e.g. allergic rash).
  • H2 and H1 blockers – both short and long-acting (diphenhydramine, hydroxyzine) for anaphylactic symptoms of MCAS.
  • Aspirin – blocks prostaglandins
  • Leukotriene antagonists – such as zafirlukast, montelukast, prescribed for respiratory spasm, skin reactions and swelling.
  • Corticosteroids – controls malabsorption, the build-up of fluid in the abdomen (ascites), bone pain and to prevent anaphylaxis.

Diet modifications

  • Avoid alcohol or limit intake – DAO activity is impaired by alcohol and can increase dietary intake from food, and may trigger MCAS symptoms.
  • Opt for Mediterranean-style diet rich in fibre and prebiotics to improve gut microbiome and increase short-chain fatty acids, which reduce mast cell activation
  • Try the low-histamine diet

Lifestyle modifications

  • Get plenty of good quality sleep
  • Avoid stimulants, drugs, alcohol, as these substances disturb the hypothalamic-pituitary-adrenal axis and can exacerbate symptoms
  • Do regular physical activity to mitigate corticotropin-releasing hormone-induced mast cell activation


Molecular and Cell Biology of Pain Angela N. Pierce, Julie A. Christianson, in Progress in Molecular Biology and Translational Science, 2015

Rudick CN, Bryce PJ, Guichelaar LA, Berry RE, Klumpp DJ. Mast cell-derived histamine mediates cystitis painPLoS One. 2008;3(5):e2096. Published 2008 May 7. doi:10.1371/journal.pone.0002096

Afrin LB. The presentation, diagnosis and treatment of mast cell activation syndrome. Curr Allergy Clin Immun. 2014 Sep 1;27(3):146-60.

Maintz L, Novak N. Histamine and histamine intolerance. Am J Clin Nutr. 2007 May;85(5):1185-96. PMID: 17490952.

Afrin LB. The presentation, diagnosis and treatment of mast cell activation syndrome. Curr Allergy Clin Immun. 2014 Sep 1;27(3):146-60.

Afrin LB, Khoruts A. Mast cell activation disease and microbiotic interactions. Clin Ther. 2015 May 1;37(5):941-53. doi: 10.1016/j.clinthera.2015.02.008.

Afrin LB, Self S, Menk J, Lazarchick J. Characterization of mast cell activation syndrome. Am J Med Sci. 2017 Mar;353(3):207-215. doi: 10.1016/j.amjms.2016.12.013.

Wang X, Liu W, O’Donnell M, et al. Evidence for the Role of Mast Cells in Cystitis-Associated Lower Urinary Tract Dysfunction: A Multidisciplinary Approach to the Study of Chronic Pelvic Pain Research Network Animal Model Study. PLoS One. 2016;11(12):e0168772. Published 2016 Dec 21. doi:10.1371/journal.pone.0168772

USD $19.95 ex GST/VAT/TAX
Jessica Lloyd - Vulvovaginal Specialist Naturopathic Practitioner, BHSc(N)

Jessica is a degree-qualified naturopath (BHSc) specialising in vulvovaginal health and disease, based in Melbourne, Australia.

Jessica is the owner and lead naturopath of My Vagina, and is a member of the:

  • International Society for the Study of Vulvovaginal Disease (ISSVD)
  • International Society for the Study of Women's Sexual Health (ISSWSH)
  • National Vulvodynia Association (NVA) Australia
  • New Zealand Vulvovaginal Society (ANZVS)
  • Australian Traditional Medicine Society (ATMS)