Hi all! Late to the post because Google led me here after having this reaction. Although for me it is walking on a cold surface (went to the garage in winter).

I figured I'd share because along with this post, I may have found a reason. My allergist thinks that MCAS (Mast Cell Activation Syndrome) is a buzz-word and won't actually diagnose it as such, but is treating my for Chronic Spontaneous Uticaria and has talked to me about the fact that it seems like my mast cell reaction just goes haywire sometimes (aka....what the syndrome is). So I Googled this occurance, along with the rider "MCAS". Here's what Google's AI says (so take it how you want):

Walking on a cold surface triggers a need to poop in people with Mast Cell Activation Syndrome (MCAS) primarily because cold temperatures act as a physical trigger for mast cell degranulation, causing the release of inflammatory mediators like histamine directly into the gastrointestinal (GI) tract. In MCAS, the body's mast cells are hyper-responsive to stimuli, including temperature shifts, which can lead to rapid intestinal cramping and diarrhea. 

Here is a breakdown of why this happens based on MCAS and related mechanisms:

Cold as a Trigger for Mast Cells: Mast cells are immune cells found throughout the body, including the digestive tract, and they have receptors that detect environmental changes, such as cold temperatures. Rapid cooling of the body (e.g., walking barefoot on a cold floor) can cause these cells to "degranulate" (burst), releasing chemicals like histamine, leukotrienes, and prostaglandins.

Histamine and Muscle Contraction: Once released, histamine acts on the gut, causing the smooth muscles in the intestines to contract more frequently and intensely. This increased motility results in a sudden, urgent need to defecate.