Mast Cell Activation Syndrome (MCAS) Signs, Testing, and Treatment Options
What is MCAS?
If you've been told your reactions are "just allergies," but they keep spreading to new parts of your body, you may have come across MCAS. More and more people are wondering if they have it. Some do. Many others have something else going on and haven't been properly evaluated. That difference matters, because the right treatment starts with the right diagnosis.
MCAS stands for Mast Cell Activation Syndrome. It is a condition where overreactive mast cells release histamine and other chemicals in response to a plethora of triggers. It is a cluster of chronic symptoms that impact multiple organ systems in the body.
MCAS may affect people who have genetic predispositions to handling histamine in ways that make them more sensitive to triggers. Common triggers include food, environmental allergies, and environmental toxicants, such as mold.
How Common Is MCAS?
The honest answer is that experts don't agree. One group of researchers and clinicians estimates that MCAS may affect up to 17% of the general population. Specialists who use the stricter consensus criteria caution that MCAS is over diagnosed in people who likely have other conditions. Which estimate you see depends largely on which diagnostic criteria are being used.
What both sides agree on: getting properly evaluated matters, so you get the right diagnosis and the right treatment.
MCAS Triggers to Watch for in Arizona
Living in the desert doesn't mean you're safe from mold and other triggers. A few local ones we look at with patients:
Monsoon season moisture. Summer storms can lead to roof leaks and water damage that create hidden mold growth.
Water-damaged buildings. Arizona doesn't have a single statewide building code. Each city and county adopts its own, so homes here were built under many different code editions, with varying enforcement and workmanship. Many homes were also designed with a dry climate in mind, and maintenance often gets put off. When intense monsoon rains do get inside, there often aren't requirements to check for hidden moisture or fully dry the building afterward. That can leave moisture trapped in walls and floors, where mold can keep growing out of sight.
Evaporative (swamp) coolers. These add moisture to indoor air during the hot months and can make homes moldier, especially if they aren't cleaned and maintained.
Desert pollen and seasonal allergies. Pollen from desert plants and seasonal dust can add to the overall burden on an already reactive immune system.
Key MCAS Symptoms
To be diagnosed with MCAS, at least 2 of these organ systems must be involved during an episode:
Heart: low blood pressure, lightheadedness, fainting
Lungs: cough, shortness of breath, wheezing
Gut: abdominal cramping, diarrhea, loose stools, or vomiting
Skin: flushing, hives, swelling (eyes, lips, tongue, throat)
Other symptoms are commonly associated with MCAS but are not used to diagnose it. You may have these symptoms and MCAS, but having them does not mean you have MCAS without a proper diagnosis:
Fatigue
Food allergies or food intolerances
Brain fog and trouble focusing
Anxiety, depression, and mood disorders
Digestive problems, such as bloating, abdominal pain, constipation, and SIBO
People with MCAS may also have other conditions, such as POTS (Postural Orthostatic Tachycardia Syndrome) and EDS (Ehlers-Danlos Syndrome).
MCAS is not the same thing as histamine intolerance, which is a separate condition. It is also different from mastocytosis, a disorder in which the body produces too many mast cells, with its own diagnostic criteria.
Diagnosing MCAS
Under the widely used consensus criteria, MCAS is diagnosed when three things are true:
Symptoms in 2 or more organ systems from the list above, happening in episodes.
Lab evidence that mast cells are releasing their chemicals during a flare. The most reliable marker is a rise in blood tryptase above your own baseline level. The consensus group's "20% + 2" formula looks for an increase of 20% over your baseline plus 2 ng/mL. Other markers, such as histamine or prostaglandin D2 and their breakdown products in urine, can also be used.
Your symptoms improve with treatments that target mast cells.
This is not always easy to assess. The blood draw has to be timed shortly after a flare and compared against a baseline drawn when you feel well. Some experts also use broader diagnostic criteria, and this remains an area of active debate. That's why a careful evaluation matters.
Conventional Medicine Treatment of MCAS
Conventional treatment may include different medications, including but not limited to:
Mast cell stabilizers to prevent mast cells from releasing histamine
Antihistamines (H1 and H2 blockers) to reduce allergy-like histamine symptoms
Leukotriene modifiers to assist with breathing
For more severe symptoms and cases, doctors may prescribe corticosteroids to reduce inflammation, epinephrine (EpiPen) to treat anaphylaxis in emergencies, and omalizumab (Xolair) for severe and ongoing symptoms.
The Naturopathic Medicine Approach to MCAS
In naturopathic medicine, we follow the therapeutic order and look at triggers and obstacles to cure. Triggers must be reduced, and patients should be removed from any toxic exposures that are pushing their immune system to respond this way. For example, if someone is living in a moldy home, they need to get out of that environment.
Other approaches include:
Diet and nutrition. A low histamine diet removes foods that can trigger symptoms. It is key for the foundation, but on its own it isn't enough for true MCAS patients.
Nettle leaf tea. Many of our patients drink nettle leaf tea as a gentle, supportive part of their plan.
Supplements. Your naturopathic doctor may recommend vitamin C, quercetin, and bromelain with nettle leaf extract, at doses and frequencies tailored to you. Not everyone tolerates quercetin well. These natural ingredients may help with MCAS, but they are typically not enough on their own.
Ketotifen. Ketotifen works as a mast cell stabilizer, helping keep mast cells from releasing histamine and other chemicals. It also has antihistamine effects. In the USA, oral ketotifen is only available through compounding pharmacies. The FDA has approved ketotifen only as eye drops, so taking it by mouth is not an FDA-approved route of administration. We typically start with a low dose to assess tolerance. Ketotifen is not for everyone, because everyone's biochemistry is different.
Cromolyn sodium. Cromolyn is available as a nasal spray and in oral forms, and can also be compounded. Compounding lets us request formulations without fillers a patient is known to react to.
Reducing exposures. We work with patients to identify and reduce the exposures in their home, food, and air that keep their immune system on high alert.
First, do no harm. Be careful with first-generation antihistamines such as Benadryl (diphenhydramine). They can cause significant drowsiness and other side effects, and older adults should generally avoid them because they raise the risk of confusion and falls. Talk with your provider before starting or stopping any antihistamine.
Wondering If MCAS Is Behind Your Symptoms?
MCAS is often missed, and it's just as often mislabeled. Getting the right answer starts with a careful evaluation, not a guess. I bring 14 years of clinical experience in environmental medicine, mold illness, hormone imbalances, autoimmunity, chronic fatigue syndrome, and MCAS. I look at the full picture: your symptoms, your triggers, your home environment, and the right lab testing to sort out MCAS from the conditions that mimic it.
You don't have to keep guessing what's setting you off. Book your appointment or free consultation with me , or call us at 928.300.1565. I see patients in Sedona and the Verde Valley, with telemedicine available across Arizona.
Medical disclaimer: This article is for general educational purposes only. It is not intended to diagnose, treat, cure, or prevent any disease, or to prescribe any medication. It is not a substitute for professional medical advice, diagnosis, or treatment, and reading it does not create a doctor-patient relationship. Always talk with your healthcare provider before starting, stopping, or changing any medication or supplement, and never delay seeking care because of something you read here. If you are having a medical emergency, call 911.
References
Valent P, et al. Definitions, criteria and global classification of mast cell disorders with special reference to mast cell activation syndromes: a consensus proposal. Int Arch Allergy Immunol. 2012;157(3):215-225. DOI
Valent P, et al. Why the 20% + 2 tryptase formula is a diagnostic gold standard for severe systemic mast cell activation and mast cell activation syndrome. Int Arch Allergy Immunol. 2019;180(1):44-51. DOI
Weiler CR, et al. AAAAI Mast Cell Disorders Committee Work Group Report: Mast cell activation syndrome (MCAS) diagnosis and management. J Allergy Clin Immunol. 2019;144(4):883-896. DOI
Afrin LB, et al. Diagnosis of mast cell activation syndrome: a global "consensus-2". Diagnosis (Berl). 2020;8(2):137-152. DOI
Dr. Samuel Madeira | Naturopath