Can Stress Trigger an MCAS Flare? How Stress Hormones Reach Your Mast Cells
How the stress hormone CRH reaches your mast cells, what human studies found, and how to track stress alongside your other MCAS triggers.
Photo: Nicolas Lobos / Unsplash
Can stress trigger an MCAS (mast cell activation syndrome) flare? Yes, it can, even when nothing new has gone into your mouth or touched your skin. Mast cells are the immune cells that release histamine and other chemicals during a reaction, and they carry receptors for corticotropin-releasing hormone (CRH). CRH is one of the first hormones your body releases under stress. That gives stress a physical route to your mast cells, which is why a flare after a hard week can be a physical event rather than something you imagined.
How a stress hormone reaches a mast cell
When you're under stress, your brain releases CRH to start the hormone chain that ends with cortisol. In 2005, Cao and colleagues reported that two kinds of lab-grown human mast cells carried receptors for CRH, and they called it the first evidence that mast cells express functional CRH receptors. In those cells, CRH triggered the release of one specific chemical, a blood vessel growth signal called vascular endothelial growth factor (VEGF), without releasing histamine or tryptase, so the effect of CRH on a mast cell can be selective rather than all-or-nothing.
Cells grown in a lab can only show so much about what happens in a person. A 2003 study in adult women applied a small dose of CRH to the skin of the forearm and measured blood flow. CRH widened the small blood vessels there, and that widening was significantly reduced in the presence of cromolyn (a medication that stabilizes mast cells) or of antihistamines that block H1 or H2 receptors. Crompton and colleagues concluded that CRH widens blood vessels in human skin through mast cells releasing their contents, mainly histamine. That study applied the hormone directly rather than stressing anyone. Still, it shows a stress hormone producing a flush-type response in human skin by way of mast cells.
What happened when researchers stressed healthy volunteers
The most direct human evidence comes from a 2014 study published in Gut. Vanuytsel and colleagues measured small intestinal permeability, meaning how easily molecules pass through the lining of the small intestine, using a sugar test: you drink two sugars, and the ratio that comes out in your urine reflects how leaky the lining is. In the first part, 23 healthy volunteers went through several conditions. Giving a public speech increased intestinal permeability, while waiting for possible electric shocks didn't. The speech also raised salivary cortisol, and the permeability change showed up only in people whose cortisol rose significantly.
In the second part, 13 volunteers were given CRH itself. CRH increased permeability on its own, and pretreatment with cromolyn blocked that increase. Cromolyn also blocked the effect of the public speech. In the authors' words, this suggests the involvement of mast cells. These were healthy people, not people with MCAS, and the study measured gut permeability rather than flares. Even so, an ordinary social stressor changed gut physiology in these volunteers, and a mast cell stabilizer prevented that change.
A 2020 review by Theoharides describes psychological stress worsening asthma, atopic dermatitis, and mastocytosis (a condition with too many mast cells), and it attributes that to mast cells responding to CRH and two other nerve-related signals, neurotensin and substance P.
Why this makes triggers harder to read
This is where trigger tracking gets complicated in clinic. After a few bad reactions, it makes sense to feel wary of anything new. That wariness is itself stress, and stress can contribute to a flare, so a new food can get the blame for a reaction that the worry about the food helped set off.
The connection may also go the other way, because mast cell chemicals may produce symptoms that feel like anxiety. In a 2025 survey, Weinstock and colleagues compared 553 people with MCAS to 558 people who had never been diagnosed with it. Women with MCAS reported higher rates of all 14 psychiatric conditions the survey asked about, and anxiety, depression, panic attacks, and post-traumatic stress disorder (PTSD) were each reported by close to half or more of them. Weinstock's team offered a theory for the overlap: mast cell chemicals that reach the brain, or that come from mast cells living in the brain, can lead to or worsen these conditions. They were also clear about the limits: participants volunteered, the diagnoses were self-reported, and none of the answers could be confirmed. So the survey shows that the two show up together often, without showing which came first. The same which-came-first question comes up in research on long COVID and anxiety.
A stress flare is a physical event
When stress hormone levels are high, mast cells can become more reactive. In one video I described this as affecting how often they release their contents, or "how trigger happy they are." Some people hear that their symptoms are all in their head and leave with nothing. Others see a clinician so worried about seeming dismissive that stress is left out of the conversation entirely. As I said in that same video, "neither of these extremes serve the patient in the middle."
When a flare shows up with no new food, medication, or exposure behind it, I look at what the nervous system was carrying beforehand, alongside every physical trigger, because the treatment differs depending on which one it was. If nervous system hypervigilance is part of the picture, then it needs care aimed at the nervous system, in addition to the medications you and your clinician have chosen.
Tracking stress next to your other triggers
If you think of your tolerance as a bucket, the way the mast cell bucket model describes it, stress is one more thing filling it. A few notes that make stress visible in a symptom log:
- A simple stress rating each day, recorded next to foods, fragrances, and medications
- Whether you were anxious about trying something new before you tried it
- Poor sleep, conflict, travel, or deadlines in the days before a flare
- Where you were in your cycle, since hormonal shifts move mast cells too
Wearable stress scores come up often in these conversations, and what a heart rate variability (HRV) score actually measures covers what that number does and doesn't reflect. The rest of this series is collected on the MCAS hub.
If you're living with MCAS and want a structured starting point, MCAS: What You Need to Know First walks through what the diagnosis actually means, where to begin, and what to do when diet alone isn't enough.
FAQ
Can anxiety cause MCAS symptoms?
The connection may go both ways. Stress hormones such as CRH act on receptors that mast cells carry, and mast cell chemicals may also produce symptoms that feel like anxiety, such as a racing heart. In a 2025 survey of 553 people with MCAS and 558 people without it, women with MCAS reported anxiety at higher rates than women without it, although a survey like that can't show which one came first.
How can I tell whether a flare came from stress or from a food?
From a single flare, you often can't. A pattern is easier to see over weeks of notes that record stress and worry next to foods, fragrances, medications, and your cycle. Bringing those notes to your clinician gives the two of you something concrete to look at together.
Does a stress-triggered flare mean my MCAS is psychological?
No. Human mast cells carry receptors for corticotropin-releasing hormone, and studies in human skin and in the human gut found that this stress hormone produced changes that a mast cell stabilizing medication reduced or blocked. A flare that follows a hard week can have a physical cause.
Can a mast cell stabilizer block a stress reaction?
In one study of healthy volunteers, the mast cell stabilizing medication cromolyn blocked the rise in gut permeability that came with giving a public speech. That was a small study of people without MCAS, and flares weren't one of its outcomes, which leaves open how a stabilizer would work for you. Any medication question belongs with the clinician who prescribes for you.
Is stress management a treatment for MCAS?
Stress work doesn't replace medical care for MCAS. When stress is part of what sets off someone's flares, I think of nervous system support as one piece of their care, alongside the medications and trigger changes they've worked out with their clinician.
References
- 1.
- 2.
- 3.
- 4.
- 5.
