Running with Mast Cell Activation Syndrome: What I Wish I’d Known About My ‘Invisible Limiter

I used to think I just wasn’t tough enough. Years later, I found out my body had been fighting me the whole time.

When I was seventeen I thought it was all in my mind. Everyone told me it was.

Every race and hard practice started and ended the same way: the same stomach pain and constant need to pass gas, the same lead legs that locked up solid like stone, the same frustration of giving everything I had and still watching someone edge past me in the final hundred meters. Looking back, I realize I was running with Mast Cell Activation Syndrome long before I had a name for it

I ran 16:48 for a 5K and 4:48 for the mile — competitive times for a D4 school in West Michigan, sure, but I always felt like there was a wall I couldn’t break through no matter how hard I worked – and I worked so hard! I trained year-round, did the workouts, pushed through pain, did the cross training, all the little things, but my body never bounced back the way everyone else’s did and never allowed me to tap into that level of fitness I had developed.

My coach, an absolutely wonderful man who I am still so close too tried everything to help me solve it. More salt, more base, more cross training, less bulk, better timing for when I reach peak. We tried and tried, but we couldn’t solve it. It just became normal.

What I didn’t know was that my body — it was fighting itself. Decades later, I would learn the word for it: Mast Cell Activation Syndrome (MCAS).

The Hidden Weight I Carried

MCAS is a condition where certain immune cells — mast cells — misfire and release inflammatory chemicals at the wrong times. For me, it means heat, humidity, pollen, and even exercise itself can trigger body-wide inflammation.

Back then, I just thought some days were “bad days” and that they just happened to almost always be race days. I thought it was nerves, fear, weakness. Now I understand they were flares. Looking back, MCAS shaped my entire running life in ways I couldn’t see:

Chronic inflammation changed how my body used oxygen.

Histamine — one of the chemicals those rogue cells release — opens some blood vessels and clamps down on others. During races, that meant oxygen wasn’t getting where it needed to go. My muscles would suddenly seize, as if I’d sprinted into a wall. Matter how hard I willed my body to put one foot in front in front of the other I couldn’t do it.

My gut was always in revolt.

Mast cells line the digestive tract, and when they’re angry, so is your stomach. Cramps, nausea, unpredictable bathroom breaks — all of it was my immune system reacting, not my diet or nerves. I never understood it, but I would spend every second I could before a race in the bathroom, trying to relieve the pressure from all the gas I had.

Heat and humidity hit like a sledgehammer.

I always have loved running in the 40s. Everyone still thinks I am crazy, but cool air is the only time my body stopped fighting itself. Now I know why. I would struggle all spring, summer and fall (the competitive seasons) and I would love training all winter. I would feel so confident going into the next year only to find that I would be zapped once again when the season came around.

Recovery took forever.

After races, while teammates bounced back, I was wrecked for days. The inflammation never really stopped — it just smoldered between workouts. In High School we would race up to three days a week and I just couldn’t do it.

If MCAS had been recognized back then — if someone had connected the dots — I might have found ways to lower the inflammation, stabilize my system, and give my body a fair shot. Maybe that 4:48 mile would have been a 4:44, which would have been two seconds below the automatic qualifying time back then to go to state.

But the point of me sharing this twofold. One, it has been incredibly validating to look back on all these lived experiences with understanding that I have now. Second, somewhere, someone is going through this right now and I want them to know and to be able to do what I couldn’t.

If you’re a runner who trains hard and still can’t understand why your body betrays you…

To the Any Runner Who Can Relate

If you love running but dread the stomach pain, the lead legs that won’t respond, the heat, the “bad days” where you just don’t have it, but you did all the little things right and you question yourself…
If the people in your life think you’re overreacting, or that quitting might be safer — You might be where I was and still am.

Please hear this: You’re not broken. You’re not lazy. You’re not imagining it. It’s not in your head.
You might be fighting a body that’s chemically out of balance, not a mind that’s weak. There are doctors who understand this now. There are tests, treatments, and tools that can help. Most importantly — you deserve support, not doubt. If you can’t find that support from anyone else, I will be that support.

Why I’m Sharing This

I don’t run for medals as much anymore. After trying to cut it for a year running for my college team I transitioned to marathons. I did pretty well for myself at first, I even got the chance to run Boston, but my issues caught up to me and I would end up with legs locked up so bad that I couldn’t finish over and over again. Eventually it got so bad that I just gave up. Now I run for peace, for understanding, and for my kids. While MCAS is still being researched, we do have emerging data that shows it’s far from rare.

My hope is that together we can raise awareness to this struggle. A 2023 clinical study found idiopathic MCAS in 4.4 percent of patients tested out of group of 703 people. (Sánchez-Muñoz et al., Annals of Allergy, Asthma & Immunology, 2023). So while MCAS is not super prevalent, it is out there and it is a real struggle. Therefore if we can reach even one athlete or parent, who is able to see the signs early — if it helps them find answers, compassion, or the courage to keep believing in themselves — then all those hard miles will finally mean something bigger than me

Author’s note:

If this story sounds familiar, visit The Mast Cell Disease Society (tmsforacure.org) or ask your doctor about mast cell activation disorders. Getting the right diagnosis can change everything — not just for your performance, but for your quality of life. If you’ve experienced something like this, I’d love to hear your story — you can comment below or reach out privately. We’re all still figuring this out.