• Welcome to Phoenix Rising!

    Created in 2008, Phoenix Rising is the largest and oldest forum dedicated to furthering the understanding of and finding treatments for complex chronic illnesses such as chronic fatigue syndrome (ME/CFS), fibromyalgia (FM), long COVID, postural orthostatic tachycardia syndrome (POTS), mast cell activation syndrome (MCAS), and allied diseases.

    To register, simply click the Register button at the top right.

Interchange of symptoms


Senior Member
Sorry for making two posts in quick succession.

I'm not sure I have MCAS but I'm exploring the possibility that mast cell activation is at play with my symptoms.

Does anybody ever experience one set of symptoms, the CFS-type symptoms for example, generally, but then when an MCAS flare is triggered by some environmental or dietary thing, the CFS goes away while the MCAS symptoms take over? Like you either have CFS or MCAS, but never both at the same time. Or is it generally that your MCAS and CFS are one and the same.



Senior Member
United Kingdom
I can only speak for myself but for me the two are intertwined - I have sort of "permanent" CFS, say 7/10, but when I get a really bad reaction to something I can go all the way up to a 10/10, if that makes sense. And it's very much not the case that the MCAS will displace my CFS; it makes it considerably worse.

And my reactions generally include symptoms that are very common with CFS (aching joints, cognitive issues, brain fog, heavy fatigue) and not all that much of the stuff that's generally associated with MCAS or allergies (hives, itching).