Why Is Allergy Testing Often Normal in MCAS? A common head-scratcher: your allergy tests come back totally normal… yet you still feel like you’re reacting to everything. What gives? Here’s the deal—in mast cell activation syndrome (MCAS), your immune system’s alarm bells (mast cells) go off even when there’s no classic allergy trigger. Most allergies involve IgE antibodies, but MCAS doesn’t follow that rule. It’s IgE-independent—meaning standard allergy tests may miss it entirely. And yet, the s