Mast Cell Activation Syndrome (MCAS)

When mast cells become over-reactive

Last reviewed: October 2026 · 64 sources

Educational only, not medical advice. This page shares general information and community experience. It isn’t a diagnosis or a treatment plan. Please talk with your doctor or another licensed healthcare provider before starting, stopping, or changing any test, supplement, medication, or treatment.

At a glance

  • What it is: a condition in which mast cells, immune cells involved in allergic reactions, release their chemical messengers too easily, causing episodes of symptoms in more than one part of the body [1, 2].
  • Common symptoms: itching, flushing, hives or swelling; dizziness or fainting; cramping, diarrhea or vomiting; wheezing or breathlessness; nasal congestion [2].
  • The big debate: two different sets of criteria are in use. The stricter “consortium” criteria diagnose relatively few people, while broader criteria diagnose many more [3, 4, 5].
  • Treatment: usually avoiding personal triggers plus medicines that block or calm mast cell chemicals, chosen with a specialist [6, 7].
  • Emergency: severe reactions can be anaphylaxis. Call 911 or your local emergency number and use epinephrine as your specialist has instructed [8].

If you have reactions that seem to come out of nowhere, such as flushing after a hot shower, hives after a stressful day, or stomach cramps and dizziness after a meal, MCAS may be one of the things you’ve read about. It is real, it can be hard to pin down, and doctors don’t all define it the same way. This page explains both views so you can have a better-informed conversation with your clinician.

What MCAS is

Mast cells are immune cells found throughout the body, especially in tissues that border the outside world, like the skin, gut and airways [9]. When they’re activated, they release chemicals such as histamine, tryptase, prostaglandins and leukotrienes that cause allergy-type symptoms [6, 10].

In MCAS, mast cells release these chemicals in episodes that affect more than one body system. A 2012 international consensus proposal described MCAS as a recurring, often severe condition with symptoms in multiple organ systems, a measurable rise in mast cell markers during episodes, and a response to medicines that block mast cell chemicals [1].

MCAS is part of a larger group of mast cell disorders. Some forms are linked to an abnormal (“clonal”) population of mast cells, as in systemic mastocytosis. Others are secondary to a known allergy. When no cause is found, it’s called idiopathic MCAS [3, 6].

Common symptoms

According to a 2025 Canadian review, typical MCAS episodes start suddenly, affect at least two body systems and settle within several hours. They often meet the criteria for anaphylaxis [2]. Symptoms can include:

  • Skin: itching (sometimes starting in the palms or soles), flushing, hives, or swelling of the lips, face or throat (angioedema)
  • Heart and circulation: dizziness, confusion, near-fainting or fainting from low blood pressure
  • Gut: abdominal cramping, diarrhea or vomiting
  • Breathing: shortness of breath or low oxygen levels
  • Eyes and nose: severe nasal congestion, runny nose, sneezing, red eyes

Source: [2]

Broader symptom lists. Clinicians who use the broader “mast cell activation disease” model list many more symptoms, including fatigue, headache, trouble concentrating, anxiety, sleep problems, muscle and bone pain, bloating, and chemical or environmental sensitivities [10]. Under the stricter criteria, symptoms like fatigue, brain fog, headache, joint pain or bloating on their own, or symptoms that are constant rather than episodic, are not considered suggestive of MCAS [2]. This is one of the main reasons people get different answers from different doctors.

Triggers, causes and risk factors

Common triggers. The Mast Cell Disease Society (TMS) lists triggers that include heat, cold or sudden temperature changes; stress; exercise; fatigue; certain foods or drinks, including alcohol; some medicines; strong odors; insect stings; infections (viral, bacterial or fungal); friction or pressure on the skin; and sunlight. Triggers vary from person to person and can change over time [11].

Causes to rule out. Allergy specialists look for secondary causes, especially food allergies that only cause reactions with “cofactors” like exercise, alcohol or anti-inflammatory painkillers (NSAIDs), and NSAID hypersensitivity itself [2].

Genetics. About 4–6% of people inherit extra copies of a tryptase gene (a trait called hereditary alpha-tryptasemia, or HαT), which raises their baseline tryptase level [2, 12]. A high baseline tryptase by itself should not be read as a sign of mast cell activation [2].

Mold. Many patients and some clinicians report mold as a trigger, and mold allergy is well recognized [13]. Research on mold and mast cells is mostly lab-based: certain molds can activate mast cells in lab studies [14, 15, 16], while at least one fungal toxin, gliotoxin, has been shown to block mast cell activation [17]. Clinical studies ranking mold as a trigger in MCAS are lacking. See our post on mold and MCAS.

How MCAS is diagnosed

The consortium criteria (stricter)

The international consensus criteria, first proposed in 2012 and updated in 2019 (often called the ECNM-AIM or “consensus-1” criteria) require all three of the following [1, 2, 3]:

  1. Typical symptoms of severe, recurrent episodes involving at least two organ systems.
  2. Lab proof of mast cell activation, preferably a rise in blood tryptase during an episode compared with your own baseline, using a standard formula (a rise of at least 20% above baseline plus a small fixed amount).
  3. Response to medicines that block mast cell chemicals or their effects.

The AAAAI’s 2019 work group report uses this approach and says it aims to diagnose most cases “without overdiagnosing the disorder in patients who likely have other conditions” [18]. Under these criteria, MCAS is uncommon. One specialist center found idiopathic MCAS in 31 of 703 people referred with a suspected mast cell disorder (4.4%) [19], and the 2019 consensus authors describe overt MCAS as “unusual” [3].

Alternative criteria (broader)

Dr. Gerhard Molderings, Dr. Lawrence Afrin, Dr. Leonard Weinstock and colleagues use a broader framework they call mast cell activation disease. It accepts a wider range of symptoms (often chronic rather than episodic) and more types of lab evidence [4, 10]. Their 2021 “consensus-2” paper estimates MCAS may affect up to 17% of people and says either set of criteria can be used [4].

Consortium experts respond that the broader criteria lack specificity and haven’t been validated, and could lead to misdiagnosis [5]. Supporters argue that strict criteria miss patients who might benefit from treatment. A 2025 study of 100 young people with POTS found MCAS in 2%, 37% or 87% depending on which criteria were used, with similar responses to treatment across groups [20].

Tests your clinician may discuss

  • Blood tryptase, drawn within about 4 hours of an episode and compared with a baseline level taken when you’re well [2]. Because episodes are unpredictable, one Canadian team suggests keeping a lab requisition for tryptase with your epinephrine auto-injector [2].
  • Urine tests for mast cell chemicals: N-methylhistamine, 2,3-dinor-11β-PGF2α (a prostaglandin product) and leukotriene E4. They can help, but they’re less specific than tryptase, and labs use different cut-offs [2].
  • Checks for other conditions, such as allergy testing, tests for HαT, and sometimes evaluation for mastocytosis [2, 3].

Who diagnoses it? Usually an allergist/immunologist; some patients also see hematologists or integrative clinicians. The Canadian review notes that only a small minority of people referred for suspected MCAS are ultimately diagnosed with it under the strict criteria [2].

Treatment approaches to discuss with your clinician

Treatment is individual and usually adjusted step by step with a specialist. These are categories for discussion, not instructions.

  • Identify and avoid personal triggers [11].
  • H1 antihistamines (the allergy-pill type). These are usually the first medicine offered, and second-generation (less drowsy) versions are generally preferred [2, 6].
  • H2 antihistamines, often added for gut symptoms, although the Canadian review notes a clear benefit has never been demonstrated [2].
  • Leukotriene blockers such as montelukast [2, 6].
  • Mast cell stabilizers such as oral cromolyn, which may help persistent gut symptoms. It’s generally well tolerated and is taken for at least a month before judging whether it helps [2].
  • Other prescription options chosen by specialists, including aspirin in selected patients and anti-IgE therapy (omalizumab) for hard-to-treat cases [6, 21]. Omalizumab isn’t FDA-approved for MCAS and carries a boxed warning about anaphylaxis [22].
  • Epinephrine for acute severe episodes and corticosteroids for prolonged ones, as directed by your specialist [6].
  • Supplements. Some clinicians suggest quercetin or vitamin C. Evidence comes from lab studies and practice-based guides rather than clinical trials in MCAS [23, 24].

Dietary approaches, such as low-histamine diets, are widely discussed in the patient community. We didn’t find clinical trials in MCAS strong enough to cite, so it’s best to talk with your clinician or a dietitian before restricting foods. TMS notes that foods can be triggers for some people [11].

Living with MCAS: practical day-to-day help

  • Keep a trigger and symptom diary, including foods, temperature, stress, activity, medicines and environments. Patterns help you and your specialist [11].
  • Have an emergency plan. If you’ve been prescribed epinephrine, know when to use it, keep it with you, and make sure people close to you know your plan [8]. A medical ID can help [8].
  • Tell every clinician and dentist that you have a mast cell disorder before procedures or new medicines. TMS has an overview of medicines used in mast cell diseases [7].
  • Make changes one at a time when you can, so you can tell what’s helping.
  • Care for your nervous system. Living with unpredictable reactions is stressful, and the Canadian review notes that anxiety can make episodes worse. That doesn’t mean symptoms are “in your head,” and support is worth seeking [2].
  • See our posts on managing MCAS flares and the MCAS + mold roadmap.

How MCAS overlaps with the other conditions

  • POTS and hEDS. Many patients and some clinicians describe MCAS, POTS and hEDS occurring together [9, 25]. The evidence is debated: a 2020 review found little original research and no shared mechanism yet described [25], and the Canadian review says these links have never been shown in people who clearly meet the consortium criteria [2]. How often MCAS shows up in POTS depends largely on which criteria are used [20]. See our overlap post and Trifecta reference.
  • Mold toxicity and CIRS. Many people with mold-related illness report mast cell symptoms. Lab research suggests a possible link, but clinical studies are limited [14, 17]. CIRS practitioners sometimes interpret signs like skin writing (dermatographia) differently [26].
  • Medication caution. A 2005 study of people with both POTS and mast cell activation concluded that beta-blockers, which are sometimes used in POTS, “should be used with great caution, if at all” in this group. If you have both conditions, talk this through with your clinicians [27].

What’s known and what’s debated

Generally accepted: mast cells can release chemicals that cause multi-system symptoms; severe episodes can be anaphylaxis; antihistamines and other mediator-blocking medicines are standard first options [1, 6, 18].

Debated:

  • Which diagnostic criteria to use, and therefore how common MCAS is: estimates range from uncommon to up to 17% of people [3, 4, 19].
  • How strongly MCAS is linked with POTS, hEDS, long COVID and mold [2, 20, 25].
  • Whether broader symptoms like fatigue and brain fog belong to MCAS [2, 10].

Functional & integrative perspective · evidence varies

The functional and integrative perspective

How functional and integrative practitioners see MCAS

These are practitioners’ own models, described in their terms. Consensus criteria for MCAS are strict [1], and mainstream experts warn that broader criteria are not validated [5], so read each one as a hypothesis.

  • A common pathway for many illnesses. Dr. Lawrence Afrin has argued that MCAS, often from complex “acquired clonality” (changes in mast cells that develop during life), could explain many chronic inflammatory illnesses, and notes that some environmental pollutants can activate mast cells [29]. Dr. Theoharides’ group has reviewed how mycotoxins affect mast cells [16]. Evidence: lab studies and expert opinion. The Canadian review lists many of these broader symptoms as “not suggestive of MCAS” [2].
  • Chemicals and the nervous system. Dr. Claudia Miller’s group proposes that fragrances and other chemicals sensitize mast cells and trigger mediator release along the smell and limbic pathways, causing “brain fog” [37]. Evidence: a hypothesis based on three case studies. See mold illness for the wider “TILT” theory.
  • The MCAS, POTS and hEDS “triad.” A 2018 review notes that EDS and POTS frequently coexist, that some of these patients have mast cell symptoms which “could represent a new specific phenotype,” and that preliminary genetic data suggest a role for tryptase [38]. Afrin writes that POTS, especially the hyperadrenergic type, has been associated with MCAS [29]. Evidence: small studies and reviews. A 2020 review found the evidence for a true link weak [25], and the Canadian review says it has never been shown in people who clearly meet strict criteria [2]. See POTS and hEDS.
  • Mold. ISEAI groups MCAS with mold illness as an “environmentally acquired illness” [28]; the lab evidence is in Triggers, causes and risk factors. Evidence: lab studies; clinical studies in MCAS are lacking [14, 17].

What functional and integrative practitioners often recommend

Functional, integrative and environmental-medicine clinicians often use the approaches below, and many patients try them. Evidence varies, and most have not been tested in large controlled trials in MCAS. Mainstream experts warn that broad MCAS criteria are not validated [5], and a 2025 Canadian review lists irritable bowel syndrome, multiple food intolerance and chemical sensitivity among conditions “not suggestive of MCAS” [2]. This is not medical advice. Please talk with a licensed clinician before trying any of them.

For practical next steps, see our MCAS + mold roadmap, MCAS flares post and how mold may trigger MCAS.

  • Looking for environmental triggers. The International Society for Environmentally Acquired Illness (ISEAI) groups MCAS with mold illness and chemical sensitivity as “environmentally acquired illness” and says treatment often involves reducing exposure [28]. Evidence: expert opinion; clinical studies in people with MCAS are lacking. The models behind this are described above. See triggers and causes above.
  • Low-histamine diet. A small study of 22 adults with chronic hives (not MCAS) found symptoms improved after four weeks without high-histamine foods, but it had no control group [30]. A German, Swiss and Austrian allergy guideline says the evidence for low-histamine diets is “extremely limited.” It advises a short, individualized, dietitian-guided approach instead of generalized, restrictive long-term diets [31]. Evidence: small uncontrolled studies, none in MCAS.
  • DAO enzyme supplements. DAO is the gut enzyme that breaks down histamine from food. An open-label pilot study in 28 people with histamine intolerance reported fewer symptoms [32]. The same guideline notes that the published studies were supported by a manufacturer, and says DAO supplementation “has not been scientifically proven to date and is not recommended” [31]. Evidence: histamine intolerance only; we found no studies in MCAS.
  • Quercetin, luteolin and other flavonoids. Dr. Theoharides’ lab found quercetin blocked human mast cell cytokine release better than cromolyn in lab tests, and it reduced skin reactions in a small human test [23]. The same lab found luteolin and a related compound inhibited human mast cells in lab dishes and in mice [33]. A treatment review by Molderings and colleagues lists flavonoids among options [24]. Evidence: lab and small human studies; no clinical trials in MCAS.
  • Vitamin C. The same review lists vitamin C as a way to increase histamine breakdown and reduce histamine formation [24]. Evidence: mechanism-based; no clinical trials in MCAS. The Canadian review’s treatment plan doesn’t include flavonoids or vitamin C [2].
  • Gut-focused approaches. A primer for gastroenterologists, co-written by Drs. Afrin and Molderings, argues that MCAS gut symptoms are often mislabeled as functional disorders like IBS. It says that beyond avoiding triggers, the best therapy targets mast cell activation and mediators [34]. Molderings’ review also suggests briefly leaving out gluten, cow’s milk protein and baker’s yeast when drug therapy starts [24]. Evidence: expert opinion and clinical experience. The German-language guideline cautions against unnecessarily restrictive diets [31].
  • Nervous-system (“limbic”) retraining. Dr. Neil Nathan writes that he has recommended the Dynamic Neural Retraining System (DNRS) to 150–200 patients, at first mainly for chemical sensitivity [35]. One small trial of a similar program in fibromyalgia and chronic fatigue reported improvements, but fewer than half of participants finished it [36]. The Canadian review notes anxiety can make episodes worse [2]. Evidence: no controlled trials in MCAS.

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The MTHFR gene and MCAS

You may see MTHFR gene results mentioned alongside histamine and MCAS. Here’s what’s known and what’s debated. For the “detox” side, see MTHFR and CIRS.

What the MTHFR gene is and what it does

Genes are made of DNA, and many of them are instructions the body uses to make proteins [39]. Most people have two copies of each gene, one from each parent [39]. A gene variant is a permanent change in a gene’s DNA [40]. It used to be called a “mutation,” but changes in DNA do not always cause disease [40]. The most common kind of variant is a one-letter change called a SNP (said “snip”) [41]. SNPs are normal: each person has roughly 4 to 5 million of them, and most have no effect on health [41].

The MTHFR gene carries the instructions for an enzyme called methylenetetrahydrofolate reductase [42]. This enzyme turns folate (vitamin B9) into its active form, 5-methyltetrahydrofolate (5-MTHF), the main form of folate in the blood [42]. Active folate supplies a methyl group so that, with help from vitamin B12, the body can recycle homocysteine, an amino acid, into another amino acid, methionine [43]. The body then uses methionine to make SAMe (S-adenosylmethionine), a methyl donor for many reactions [43, 44].

  1. Step 1
    Folate (vitamin B9) comes from food.
  2. Step 2
    The MTHFR enzyme turns it into active folate (5-MTHF).
  3. Step 3
    Active folate and vitamin B12 recycle homocysteine into methionine.
  4. Step 4
    Methionine is made into SAMe.
  5. Step 5
    SAMe donates methyl groups (methylation).
How MTHFR fits in, simplified. The real pathway has more steps and feedback loops [43].

Methylation simply means attaching a tiny chemical tag, called a methyl group, to another molecule [45]. On DNA, these tags help turn genes on or off [45]. SAMe also supplies methyl groups to neurotransmitters (the brain’s chemical messengers), proteins and other molecules [43]. For example, the enzyme HNMT breaks down histamine by methylation, using SAMe [46].

The two best-known MTHFR variants, C677T and A1298C, are named for their place in the gene and the DNA letter that changed [42, 47]. They are very common: more people in the U.S. have one or two copies of C677T than don’t [47]. Having one copy of a variant is called heterozygous, and two copies homozygous [48, 49]. One copy of each variant is called compound heterozygous [50]. In lab tests, the C677T enzyme works at about 65% of normal with one copy and about 30% with two [51]. A1298C has a smaller effect: two copies leave about 60% of normal activity [51, 52], and one copy of each variant left 50–60% in one study [52].

When MTHFR works more slowly, homocysteine can build up, mainly in people with two copies of C677T [42]. Folate, vitamin B12 and vitamin B6 all help break down homocysteine, so B-vitamin levels matter too [53]. Researchers have reported that people with two copies of C677T have higher homocysteine mainly when their folate status is low; with enough folate, homocysteine is low regardless of genotype [52, 54]. A1298C alone has not been linked to higher homocysteine [55].

A variant is not a disease or a diagnosis. Most gene variants have no effect on health [56], and ACMG says one copy of C677T, two copies of A1298C, or one of each is “unlikely to be of clinical significance” [50]. Because HNMT depends on methylation, one review has proposed a link between folate, methylation and histamine, as described below [57].

What mainstream medicine says

The American College of Medical Genetics and Genomics (ACMG) says MTHFR testing “has minimal clinical utility” and should not be part of a routine workup for blood clots [50], a position it reaffirmed in 2020 [58]. The American College of Obstetricians and Gynecologists (ACOG) does not recommend MTHFR or fasting homocysteine screening in pregnancy [59]. ACMG also warns that it is “not uncommon” for medical problems to be “incorrectly attributed to positive MTHFR status” [50]. The CDC says people with MTHFR variants “can process all types of folate, including folic acid,” and calls the advice to avoid folic acid “not true” [47].

MedlinePlus says a homocysteine blood test may be ordered if you’re at high risk for low vitamin B12 or folate, though routine screening for heart disease risk “isn’t recommended for everyone” [53].

Functional & integrative perspective · evidence varies

How some practitioners connect MTHFR and histamine

  • Histamine breakdown uses methylation. The body breaks down histamine mainly through two enzymes, DAO and HNMT [46]. HNMT works by methylation and needs S-adenosyl methionine (SAMe) as its methyl donor [46]. DAO is the main enzyme for histamine from food, while HNMT works only inside cells [60]. Evidence: established biochemistry.
  • The MTHFR–histamine idea. A 2019 narrative review by an author at Kaiser Permanente proposed a possible link between folate, methylation and histamine clearance in people with mast cell–related bladder pain (interstitial cystitis) [57]. The idea joins two established facts: MTHFR helps make methionine [42], and HNMT relies on a methyl donor [46]. Evidence: a hypothesis in one narrative review; not tested in people with MCAS [61].
  • Methylation “support.” A review co-written by an author at the Institute for Functional Medicine lists folate, vitamin B12 and vitamin B6 among the nutrient cofactors for methylation, while urging caution because of “the limitations of current research” [62]. Evidence: a narrative review; we found no studies of MTHFR in MCAS [61].

Where the evidence stands: We searched PubMed in October 2026 for MTHFR together with mast cell activation or mastocytosis and found no published studies [61]. ACMG notes there is “no evidence that specific treatments reduce risks associated with hyperhomocysteinemia or MTHFR genotype status” [50].

What to do next

General information, not a diagnosis or a treatment plan. A licensed clinician can tell you which of these steps fit you.

  1. Step 1Start this week

    • Keep a trigger and symptom diary that includes foods, temperature, stress, activity, medicines and environments [11].
    • AHRQ suggests writing down all your questions and concerns before a visit [63].
    • Our symptom checklist can help you organize what you notice.

  2. Step 2Choose who to see

    • Start with your primary care doctor: AHRQ calls your doctor “the first person to ask” [63].
    • MCAS is usually diagnosed by an allergist/immunologist [2].
    • The Mast Cell Disease Society (TMS) has patient information on testing and treatment [7, 64].
    • See also the provider directories on our homepage.

  3. Step 3Tests to ask about

    • Ask about a baseline blood tryptase and another one drawn soon after an episode, since consensus criteria prefer a rise in tryptase compared with your own baseline [2, 3, 64].
    • Urine tests for mast cell chemicals can help, but they’re less specific than tryptase [2]. TMS accepts certain urine tests as an alternative and doesn’t endorse other mediator tests until they’re proven valid [64].
    • Two sets of diagnostic criteria are in use, so ask which one your clinician is using [3, 4, 5]. Evidence: criteria debated.

  4. Step 4Everyday steps mainstream sources support

    • Identify and avoid your personal triggers [11].
    • If you’ve been prescribed epinephrine, keep it with you and make sure people close to you know your plan [8].
    • Medicines are chosen and adjusted step by step with a specialist [6, 7].

  5. Step 5Prepare for the appointment

    • Bring a list of all the medicines you take [63]. Our Doctor visit prep sheet has space for your episodes and past results.
    • If you feel dismissed, consider a second opinion: AHRQ says wanting one “is not pushy or rude” and suggests asking for a doctor who doesn’t work in the same office [63].
    • TMS is a patient organization focused on mast cell diseases [7, 11].
    • Then use the Questions to ask your doctor below.

  6. Step 6When to get urgent care

    • Call 911 for signs of anaphylaxis, such as trouble breathing, throat or tongue swelling, dizziness or passing out, and use epinephrine as your specialist has instructed [8].
    • See the full list under When to get urgent help.

Questions to ask your doctor

  • Which criteria are you using to evaluate me for MCAS, and why?
  • Could an allergy, a medicine reaction or another condition explain my episodes?
  • Should I get a baseline tryptase, and how do I get a blood test during an episode?
  • Would a homocysteine, vitamin B12 or folate blood test be useful for me, and would MTHFR testing change anything about my care?
  • Which medicine should we try first, how long before we judge it, and what side effects should I watch for?
  • Do I need an epinephrine auto-injector and a written emergency plan?
  • Are any of my current medicines a concern with a mast cell disorder?

When to get urgent help

Call 911 or your local emergency number for signs of anaphylaxis, such as trouble breathing, wheezing or high-pitched breathing sounds, trouble swallowing, swelling of the face, eyes or tongue, dizziness, slurred speech, or passing out [8]. If you have been prescribed epinephrine, use it according to your specialist’s instructions. MedlinePlus notes there’s no reason not to use epinephrine in a severe allergic reaction [8].

Sources

Numbers in brackets in the text link to these sources. Links were checked in October 2026. Some sources are written by people who support a particular approach; we've tried to say so in the text.

  1. Valent P, Akin C, Arock M, 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. PMID: 22041891. https://pmc.ncbi.nlm.nih.gov/articles/PMC3224511/
  2. Lee E, Picard M. Diagnosis and management of mast cell activation syndrome (MCAS) in Canada: a practical approach. Allergy Asthma Clin Immunol. 2025;21:49. PMID: 41272881. https://pmc.ncbi.nlm.nih.gov/articles/PMC12639879/
  3. Valent P, Akin C, Bonadonna P, et al. Proposed Diagnostic Algorithm for Patients with Suspected Mast Cell Activation Syndrome. J Allergy Clin Immunol Pract. 2019;7(4):1125-1133.e1. PMID: 30737190. https://pmc.ncbi.nlm.nih.gov/articles/PMC6643056/
  4. Afrin LB, Ackerley MB, Bluestein LS, et al. (incl. Weinstock LB, Molderings GJ). Diagnosis of mast cell activation syndrome: a global "consensus-2". Diagnosis (Berl). 2021;8(2):137-152. PMID: 32324159. https://doi.org/10.1515/dx-2020-0005
  5. GĂĽlen T, Akin C, Bonadonna P, et al. Selecting the Right Criteria and Proper Classification to Diagnose Mast Cell Activation Syndromes: A Critical Review. J Allergy Clin Immunol Pract. 2021;9(11):3918-3928. PMID: 34166845. https://doi.org/10.1016/j.jaip.2021.06.011
  6. Castells M, Butterfield J. Mast Cell Activation Syndrome and Mastocytosis: Initial Treatment Options and Long-Term Management. J Allergy Clin Immunol Pract. 2019;7(4):1097-1106. PMID: 30961835. https://doi.org/10.1016/j.jaip.2019.02.002
  7. The Mast Cell Disease Society (TMS). Medications to Treat Mast Cell Diseases. Web page, accessed October 10, 2026. https://tmsforacure.org/treatments/medications-treat-mast-cell-diseases/
  8. MedlinePlus (U.S. National Library of Medicine). Anaphylaxis. Web page, accessed October 10, 2026. https://medlineplus.gov/ency/article/000844.htm
  9. Seneviratne SL, Maitland A, Afrin L. Mast cell disorders in Ehlers-Danlos syndrome. Am J Med Genet C Semin Med Genet. 2017;175(1):226-236. PMID: 28261938. https://doi.org/10.1002/ajmg.c.31555
  10. Molderings GJ, Brettner S, Homann J, Afrin LB. Mast cell activation disease: a concise practical guide for diagnostic workup and therapeutic options. J Hematol Oncol. 2011;4:10. PMID: 21418662. https://pmc.ncbi.nlm.nih.gov/articles/PMC3069946/
  11. The Mast Cell Disease Society (TMS). Symptoms and Triggers of Mast Cell Activation. Web page, accessed October 10, 2026. https://tmsforacure.org/signs-symptoms-triggers/symptoms-and-triggers-of-mast-cell-activation/
  12. Lyons JJ, Yu X, Hughes JD, et al. Elevated basal serum tryptase identifies a multisystem disorder associated with increased TPSAB1 copy number. Nat Genet. 2016;48(12):1564-1569. PMID: 27749843. https://pmc.ncbi.nlm.nih.gov/articles/PMC5397297/
  13. American Academy of Allergy, Asthma & Immunology (AAAAI). Mold Allergy (patient page; updated July 8, 2026). https://www.aaaai.org/conditions-treatments/allergies/mold-allergy
  14. Kritas SK, Gallenga CE, D'Ovidio C, et al. Impact of mold on mast cell-cytokine immune response. J Biol Regul Homeost Agents. 2018;32(4):763-768. PMID: 30043558. https://europepmc.org/article/MED/30043558
  15. Urb M, Pouliot P, Gravelat FN, Olivier M, Sheppard DC. Aspergillus fumigatus induces immunoglobulin E-independent mast cell degranulation. J Infect Dis. 2009;200(3):464-472. PMID: 19527167. https://doi.org/10.1086/600070
  16. Ratnaseelan AM, Tsilioni I, Theoharides TC. Effects of Mycotoxins on Neuropsychiatric Symptoms and Immune Processes. Clin Ther. 2018;40(6):903-917. PMID: 29880330. https://doi.org/10.1016/j.clinthera.2018.05.004
  17. Niide O, Suzuki Y, Yoshimaru T, et al. Fungal metabolite gliotoxin blocks mast cell activation by a calcium- and superoxide-dependent mechanism. Clin Immunol. 2006;118:108-116. PMID: 16213796. https://doi.org/10.1016/j.clim.2005.08.012
  18. Weiler CR, Austen KF, Akin C, 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. PMID: 31476322. https://doi.org/10.1016/j.jaci.2019.08.023
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