But is there a biological mechanism for "building up a tolerance"? Seems possible that building up a tolerance is merely a mental exercise as well. Perhaps in the subconscious part of the brain at least.
Yup! There’s a neurotransmitter for registering the compounds that trigger that hot sensation, and that neurotransmitter gets depleted over time, based on exposure. I don’t know the exact timeframes, but it’s on the order of days/weeks.
Is it something similar for temperature? In my country some people go swimming all year around - even when the lake is covered in ice (they cut a hole). They say if you go everyday from summer to winter, you don't notice the temperature change and it's not such a big deal.
I’m not aware of anything like Substance P for temperature sensation. If I had to guess, it sounds more physiological— circulatory system adaption to handle colds exposures (e.g. blood vessel diameter). Maybe someone else here knows more and we can both learn!
Good question, one that I don't know the answer to. But I know an experiment that can help us find out! Spicy-hot is a complex phenomenon, but it is my understanding that a large part of it is that the capsaicinoids react with the heat receptors in your mouth to adjust their baseline temperature; making them react to normal temperatures inside your mouth as if they were physically burning hot. If tolerance is a purely mental exercise, then I would expect that I would not be able to accurately judge temperature of things in my mouth after consuming very spicy food; if I can accurately judge temperature then this would suggest that there is a biological mechanism at play.
I eat very spicy food and I've noticed for a while now I've lost the ability to detect when I'm being burned in my mouth (at all, it's actually a bit of an issue sometimes). The rest of my body is the same as it always was - save for my fingers, which I can use to flip things in hot oil (probably a result of exposure to hot oil). Perhaps you are on to something :)