In English, the word “hot” means hot, in the sense of high temperature, and also for spicy. It thus characterizes the perception of food containing chili, for example. The origin of this English tea kettle is probably that the sensory impressions of hot and spicy are quite similar. But do they really do the same thing biologically, so that spicy food can burn the tongue just as much as hot?
“Yes and no,” is the answer from Jan Siemens, professor at the Institute for Pharmacology at the University of Heidelberg. Yes, because when eating spicy food, biological signaling pathways are set in motion that are identical to those for hot food: “The central molecule here is the TRPV1 receptor, for the discovery of which the Nobel Prize in Medicine was awarded almost two years ago,” says Siemens. This receptor is a protein molecule located in the cell membrane of pain fibers.
It reacts to both heat and capsaicin, the substance that defines the heat in chili peppers, among other things. Then it changes its structure so that sodium and calcium ions flow into the cells and start molecular processes that mediate pain and cause inflammation-like processes. Persistent stimulation of the receptors with capsaicin, as in the capsaicin patches that can be used to relieve chronic pain, even leads to the long-term degradation of the pain fibers. At this point it is not possible to distinguish whether heat or sharpness triggered these processes.
“But on the other hand, the answer to the initial question is no,” explains biochemist Siemens. “Because hot things activate other processes beyond the TRPV1 receptor.” In addition to activating additional receptors, heat can lead to longer-lasting and significantly more severe tissue damage than capsaicin. The inflammatory reactions in real burns also go beyond the level of capsaicin triggering. Because the immune system is often involved, so that the reaction is more extensive and lengthy.
For the sensory impression on the tongue when eating spicy or hot food, this means: Hot food leaves a very similar impression to spicy food, but has even more biological effects.
