Please stop calling MCAS rare

Maybe it’s the pain and prednisone, but I’ve been really peeved by the eagerness to raise awareness for mast cell activation syndrome (MCAS) on Rare Disease Day.

First of all, why isn’t the MCAS community half as engaged on Mast Cell Disease Awareness Day? 

Second, there is growing evidence that MCAS is not rare. Some researchers believe more than 5% of people have MCAS! Yes, some organizations currently categorize MCAS as rare, but only because that is the default categorization for newly-recognized diseases. For example, AIDS used to be categorized as a rare disease. Furthermore, there is growing evidence that conditions like fibromyalgia, which affects 3-6% of people, are symptoms of MCAS.

“MCAS is likely prevalent” – Lawrence B. Afrin

Calling MCAS rare is not only unfounded, but it hurts diagnosed and undiagnosed MCAS patients. It signals to doctors that they do not need to learn about the disease. It signals to drug companies that there is not enough of a demand for new, lower cost treatments, like ketotifen in the U.S. It delays the development of accessible diagnostics. It signals to policy makers, who often vote based on numbers, that they do not need to listen to us.

Worst of all, calling MCAS rare discourages undiagnosed patients from getting tested and learning about MCAS, because they believe it is improbable.

That being said, please support Rare Disease Day. At this time, MCAS patients experience many of the same struggles associated with rare disease. Furthermore, mastocytosis continues to be classified as a rare disease through evidence-based research and we definitely should support fellow mast cell disease patients. After all, mastocytosis provides the foundation for understanding MCAS. Finally, you don’t have to have a rare disease to support Rare Disease Day.

MCAS is rarely diagnosed and rarely researched, but please stop calling MCAS rare. Instead, start planning for Mast Cell Disease Awareness Day on October 20. I know I am.

Learn more about Rare Disease Day at

3 thoughts on “Please stop calling MCAS rare

  1. I said the same thing on my Facebook page yesterday. Drives me nuts. Also, I wish they’d stop saying Ehlers-Danlos Syndrome/HSD is rare. It’s vastly under-diagnosed, not rare!

  2. Thank you for this. At now 81, with MCS and COPD, I appreciated Esp. the reasoning you gave re the downplaying, ignoring etc.on this, and too many others conditions. Although I’ve always been a “Holistic Believer” I’m not much of a scientific researcher. But I’ve read, met and been so helped by some great holistic physicians. These wonderful people were pioneers and never stopped researching, no matter how “rare” or
    “unknown”” a condition happened to be.

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