Mast cell activation syndrome, and what is actually known about it
Mast cells are immune cells that sit in the skin, gut, airways and around blood vessels. They store histamine and other chemicals and release them when triggered. In mast cell activation syndrome they release them too readily, and the result is repeated episodes affecting more than one part of the body at once.
This site indexes the treatments and triggers discussed for it. For each treatment it separates mechanism, mast-cell relationship, study type, studied condition, approval, and evidence limits instead of compressing them into a score. It carries no dosing and never says anything works. Every term used here is defined, and the rules are enforced by the build.
Where to start
I think I might have this
There is no symptom checklist here, and that is deliberate. These symptoms overlap several commoner conditions, so a list would invite a conclusion the evidence cannot support. What a diagnosis actually requires is a different question, and a more useful one.
- Read what a diagnosis requires — three criteria, and two competing versions of them.
- Note the timing of the tests. The main blood test only means something if it is drawn within a few hours of an episode.
- Find someone to take it to, then build a sheet to bring.
I have a diagnosis
The directories below are the reference material. Two things are worth knowing before reading them.
- Nothing is approved for MCAS itself. Most entries draw their studies from another condition or from laboratory work, and each one says where.
- Food lists disagree with each other, and the directory shows where they conflict rather than hiding it.
- The appointment sheet prints selected entries with their mechanisms and citations.
None of this is medical advice, and no page here can tell you whether you have this condition.
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Medications 34
Mast cell stabilisers, antihistamines, and kinase inhibitors, with their mast-cell relationship, cited study types and named conditions kept separate.
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Supplements 8
Held to the same sourcing bar as medications, with laboratory findings kept visibly separate from human studies and approval.
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Food & triggers 54
FODMAP, histamine, oxalate and tyramine ratings shown per source, with the basis for each exclusion recorded rather than assumed.
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Resources 12
Diagnostic criteria, key papers, and patient organizations, each tagged with what it is and when it was last checked.
How to read an entry
Nothing here is approved for MCAS, and almost nothing has been tested in it. Only 11 of 42 entries have been studied in MCAS patients at all, and even those are uncontrolled. So every entry separates how the treatment relates to mast cells, the types of studies cited, the conditions studied, regulatory approval and what the evidence cannot establish.
The first of those carries a distinction worth knowing before you ask about anything: 5 of these act after mast-cell mediators are released. That includes routine antihistamines and emergency epinephrine. The relationship says where an intervention acts, not how important it is, and it is never shown as a strength score.
- MCAS patients Studied in people diagnosed with mast cell activation syndrome. Current evidence consists of case reports, uncontrolled series, or retrospective review rather than randomised comparisons — so it establishes that people have taken it, not that it worked.
- Mast cell disease Studied in patients with a different mast cell disease, usually systemic mastocytosis. Those disorders have diagnostic criteria and disease biology that differ from MCAS, so a result there does not establish an MCAS outcome.
- Mast-cell-mediated condition Given to people with a condition in which mast cells are central to the disease process, with a human mast-cell effect also measured. This is human evidence, but it is not evidence in MCAS or in a clonal mast cell disorder, and it cannot establish an MCAS outcome.
- Mast cells in the laboratory Studied on mast cells directly, but in cell culture or animals rather than in people. The study-design field distinguishes human cells from non-human models. A mechanism demonstrated in a dish is a reason to investigate, not a result — and the concentrations used are frequently ones that human exposure does not reach.
- Related inflammatory condition Studied in people with a condition in which mast cells can contribute, but the study did not measure an effect on mast cells. This is a clinical bridge for inclusion, not a direct observation of mast cells and not an MCAS outcome.
- Downstream of the mast cell Acts after mast-cell mediators are released rather than stabilising the mast cell itself. This includes treatments that block mediator receptors, degrade a mediator, or oppose the physiology of an acute reaction. It describes where the intervention acts, not its clinical importance.
What the site refuses to do
- Average away a disagreement
- Published food lists contradict each other more than patients are usually told, and the sharpest conflicts are between a list and a laboratory: 60% of reviewed low-histamine diets exclude citrus, which contains no detectable histamine. Ratings are stored and shown per source so those conflicts stay visible instead of being averaged into one confident-looking number.
- Let borrowed evidence pass as its own
- MCAS relapses and remits, so improvement after starting something is not evidence that the something caused it. Every entry must state in plain words what its evidence cannot establish, and the schema rejects any that omits it. Listing a condition as approved requires citing the current label; listing one as trialled requires citing the published trial. A registered protocol or a study stopped after two participants is a fact about a trial, not a result from one.
- Trust an aggregator for a trial status
- Trial statuses come from ClinicalTrials.gov or the sponsor, never from a tracker site — the data model has no field value for one. Aggregators cache the last confident-sounding status and show it long after the underlying record has gone quiet.
- Go stale quietly
- All 153 citations are re-checked weekly by a scheduled job, and every entry displays the date a human last verified it. Entries that fall out of date say so on their own faces.