MCAS and POTS Together: What to Log on Shared Days

Updated 10 October 2026

Someone living with mast cell activation syndrome who also has postural orthostatic tachycardia syndrome may find that a bad day is hard to label. A flush, a racing heart, lightheadedness and a stomach upset can arrive on the same afternoon, and each condition has its own language for them. A record that keeps both kinds of notes under one date makes it easier to describe the day later.

This guide sets out what Dysautonomia International, Johns Hopkins Medicine, the Mast Cell Disease Society and two NIH-hosted studies say about the two conditions appearing together, then offers a table of the statements, a shared-day table, a word list, four steps and a one-page summary. It covers what happened and what you were told. A clinician decides whether the two conditions are linked in your case, and nothing here diagnoses a cause or advises on treatment.

What patient groups, NIH-hosted studies and Hopkins say about MCAS and POTS together

Dysautonomia International writes: "There seems to be a growing awareness in the medical and patient community that some patients with postural orthostatic tachycardia syndrome (POTS) also have mast cell activation syndrome (MCAS)." The sentence describes awareness among clinicians and patients, and it stops short of saying how often or why.

The numbers vary with the method. In a study in the Journal of the American Heart Association, hosted by NIH PMC, 42% (29 of 69) of patients initially diagnosed with POTS had both additional symptoms and at least one elevated biochemical marker suggesting a mast cell activation disorder. A later review in Frontiers in Neurology, also on PMC, reports that the frequency of MCAS ranged from 2% using one set of consensus criteria, to 37% using a stricter set, to 87% using clinical criteria. Those figures describe how the definition changes the count, and they say nothing about any one person.

Johns Hopkins Medicine says recent research has highlighted an overlap between POTS, joint hypermobility and mast cell disorders, some of which have a genetic origin. On the mast cell side, the Mast Cell Disease Society says any patient with a mast cell disease can potentially react to any trigger, and triggers can change over the course of the disease.

Taken together, the pages describe two conditions that are discussed side by side, with unsettled numbers and no instructions for a single day. A dated record of what you noticed and what you were told gives a clinician the facts that these general statements leave out.

Any thought about how the two conditions show up on a day can be written in your own words in the Daily Journal of MCAS Journey (by Health Journey Labs), under the date it came to you.

A table of the statements: what each source says about the two conditions and how far it goes

Each source speaks to a different part of the question, and the table sets out who says what and what kind of statement it is.

Source statements table, by MCAS Journey

The table shows agreement that the two conditions can occur in the same person, and wide disagreement about how often. The 2% and 87% in one review come from different criteria, so the number depends on who is counting and how. None of the statements describes a cause for any one day, and none gives a rule for what to do.

Logging does not settle that question. It records what each day looked like, with the facts a clinician may ask for, such as the heat, the time spent upright and the symptoms that followed. The guide to starting to track MCAS reactions describes a light first step for the reaction side of the record.

Allergy workups and other test dates fit into My Labs in MCAS Journey, so those dates sit in the same history as the reaction days around them.

A shared-day table for the clinician: reactions and upright symptoms under one date

With one row per day, a clinician can follow both kinds of symptoms in order. The columns below hold what happened and what the day looked like, and the sample rows only show the layout.

Shared-day table, by MCAS Journey

Write the date, the reaction in your own words, the upright symptom in your own words and the surroundings of that day. Add what a clinician said, with the date, and keep your question beside it. Mark guesses as guesses and leave gaps empty.

After a few weeks, read down the columns. A clinician may spot days in which both columns are full, and days in which only one is. The table only records what happened. What the pattern means is for the clinician to say. The guide to preparing for a short MCAS visit with reaction notes shows a way to turn the table into a short visit page.

Reaction lines and heart-rate context can both be saved in the Daily check-in of MCAS Journey, and a day that clearly stands out can be flagged in the Flare Tracker with a short note.

Words for shared days: heat, standing, food and illness as the clinician may ask about them

A clinician will ask what was happening around a bad day, and a short list of words helps you answer in the same terms each time.

Words for shared days

MCAS Journey keeps reaction words separate from standing words.

• Reaction words: flush, itch, hives, swelling, stomach upset, breathing worry, as I would describe it.
• Upright words: lightheaded, faint, racing heart, fog, shaky, after standing, after sitting a long time.
• Heat and surroundings words: warm room, hot shower, sun, cold, sudden change, crowded place.
• Food and drink words: meal, skipped meal, new dish, alcohol, caffeine, as recorded.
• Other words: exercise, tiredness, a cold or infection, stress, a scent, whatever fits.

Pick the words that match what you noticed and write them with the date. When a word is a partial fit, put it in quotation marks to remind yourself it was a best guess.

The lists draw on the circumstances the sources name. MCAS Journey reviewed the trigger list of The Mast Cell Disease Society, which names heat, cold or sudden temperature changes, exercise, fatigue, food or beverages and infections among potential mast cell triggers (Source: tmsforacure.org.) Hopkins says POTS symptoms typically get worse in warm environments, in situations with a lot of standing, and when you get a common cold or an infection. A clinician may phrase things differently, and will say so. The Mast Cell Disease Society also notes that some anaphylaxis symptoms can be life-threatening, which is a reason to call your local emergency number first and write afterwards.

Words and context can go into the Daily Journal of MCAS Journey as you say them, dated, so a clinician hears the day as you described it.

Four steps ahead of the appointment where both MCAS and POTS are discussed

Visits that cover two conditions are short for the amount of ground, and a few steps before the day make the table easier to hand over.

Steps before the appointment, by MCAS Journey

1. Fill in the shared-day table for the weeks since the last visit, leaving blanks where you are unsure.
2. Mark the days on which both columns were full, and the days that stood out in either column.
3. Add the dates of any tests and what you were told about them, in the words you were given.
4. Pick two or three questions for the clinician and lead with the one you most want answered.

From MCAS Journey, we recommend finishing the table the day before the visit (MCAS Journey shared days), so the latest rows are on the page.

Questions can stay descriptive. You might ask which clinician looks after which part, whether the table gives them what they need and what to bring next time. The sources do not answer questions about your own case, and the clinician is the person who can.

Write down the answers during the visit with the date, so the next appointment starts from them. The guide to what to log after an MCAS reaction day lists other items for the bag.

Questions picked beforehand can wait in My Care Team within MCAS Journey, and the Doctor Report condenses the table into one page for the visit.

A summary sheet across the weeks: reaction days, upright days and the days they coincide

A single page lets the clinician see the shape of the weeks before the first question is asked. Keep it to one side, and leave the daily rows in your bag for any question about a specific day.

Summary across the weeks, by MCAS Journey

• The weeks the table covers and the number of days that carried reactions, upright symptoms or both.
• Three or four of the most telling days, each in a line with its date, reaction, upright symptom and surroundings.
• The heat, food, illness or standing context that came up most often, as you recorded it.
• Tests and what you were told, with dates.
• What you would like to understand better, in your own words.
• Two or three questions for this visit.

Give the clinician the page when you sit down and offer to go through it together. If the clinician names something to note, add it with the date, so the next summary builds on this one. Keep your own copy as well.

What this page carries is a sequence of events plus the replies you received. Whether the two conditions are connected in your case, and what follows from that, belong to the clinicians. Breathing difficulty, fainting or a rapidly spreading reaction is a reason to call your local emergency number first, and the page can wait.

Entries, dates and your chosen questions leave MCAS Journey as a single page through the Doctor Report, ready to hand across when the visit opens.

How MCAS Journey can help

A paper table is enough to begin. If you want reactions, upright notes and visit questions in one dated history, the best MCAS apps guide compares the options.

MCAS Journey is a personal mcas tracker from Health Journey Labs on the App Store and Google Play. Several dated rows beat recollection when a visit has two conditions to cover. Your clinicians read the pattern, and the table supplies the dates, the words and the surroundings as they occurred. Below is what you can use and how each part helps.

• Food Tracker — Logs meal or drink lines; read together with reactions, flush, gut, sleep, energy.
• Flare Tracker — Logs flag a day clearly worse than the usual hard week, onset, intensity, short note; app-specific items: flush, itch, gut, breathing worry, a stacked heat-and-food episode; read together with history across weeks (one-off spike vs repeating pattern).
• Daily check-in — Logs physical symptoms, emotional state, nutrition, sleep, exercise, meds, external factors; app-specific items: skin, gut, heart-rate context, heat or environment, reaction aftermath; read together with the rest of the logged history.
• Daily Journal — Logs free-text notes, voice entry; app-specific items: what the reaction limited, heat or food context, partner talks, visit debriefs, leftover fear after an episode, a look-fine mismatch line; read together with scores and other logged history (adds context).
• My Meds — Logs medicine names, timing, dose; app-specific items: antihistamines or other options you already take as directed; read together with reaction weeks, sleep, heat days, the rest of the tracked history.
• My Labs — Logs result dates; app-specific items: tryptase, other mast-cell-related labs, allergy workups; read together with reactions, function.
• Weekly Goals — Logs one small aim, whether it held; read together with real check-ins.
• Learn — Logs short education topics, prompts; app-specific items: heat, food stacks, pacing after episodes, visit prep, reaction days that look fine afterward; read together with your own logged weeks.
• AI companions — Logs Clara (general chat), specialist companions; app-specific items: knowledge, fitness, nutrition, relationships; read together with your logged history (companions already see it); used for: visit wording; a calm partner script; a soft rain-check line; a listening ear after a hard reaction night.
• My Care Team — Logs clinicians, short visit notes; app-specific items: tends to ask mainly about anaphylaxis risk rather than day-to-day stacks; read together with logged history; used for: visit prep (what to ask and bring); notes during the visit; review afterward.
• Doctor Report — Logs one-page summary exported from logged history; app-specific items: dates, reactions, heat and food context, how you functioned; read together with the history already logged; visit type: allergy or immunology.
• My Assessments — Logs structured check-ins beyond daily scores, onboarding life and social context; read together with ongoing history.
• Weight Tracker — Logs scale or body notes; read together with the rest of the logged history.
• Period Tracker — Logs start and stop dates, flow, how heavy or light bleeding felt; read together with reaction, heat, sleep, everything else logged.

Everything you log builds one history, and insights get stronger as it grows. Custom symptoms let you add your own labels.

Sources

• Dysautonomia International: a tale of two syndromes, POTS and MCAS
• Journal of the American Heart Association (NIH PMC): mast cell activation in POTS
• Frontiers in Neurology (NIH PMC): MCAS frequency in POTS
• The Mast Cell Disease Society: symptoms and triggers of mast cell activation
• Johns Hopkins Medicine: postural orthostatic tachycardia syndrome

FAQ

The answers below draw on the sources cited in this guide, and the app they mention is MCAS Journey (by Health Journey Labs).