Spicy foods are notorious for leaving an exquisite burning sensation in our mouths. But why do our mouths feel like it's engulfed in flames even if these foods are not physically giving off heat?
The painful burning sensation associated with spicy foods is due to the capsaicin molecules that are most concentrated in the seeds of peppers. We can't actually taste the capsaicin; rather we feel them on our tongues, which are lined with receptors called TRPV1 that activate in the presence of capsaicin.
Once bound to TRPV1 receptors, capsaicin triggers signals in the brain can make it feel as though your mouth is on fire. The same signals can be elicited by these receptors in the presence of physical heat, hence why the resulting sensations from eating hot peppers is often described as a burn. Also, have you ever touched your eyes after cutting a pepper? You feel that same burning sensation because the TRVP1 receptors exist elsewhere on the body, which is why you should always wash your hands after handling hot peppers!