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Sichuan pepper is a widely-used condiment. It has a citrus-like flavour and induces a tingling numbness in the mouth, which has been found to be due to the presence of a chemical called hydroxy-alpha sanshool.

However, unlike chilli pepper, the biochemical pathways which cause the burning / numbing sensations are currently unknown.

The chemical structure of hydroxy-alpha sanshool is similar to that of capsaicin, but the mechanism of action by which it induces nerve sensations has been a matter of debate. Although the compound is an agonist at the pain integration channels TRPV1 and TRPA1 like capsaicin, newer evidence suggests that the tandem pore domain potassium channels KCNK3, KCNK9, and KCNK18 are primarily responsible for sanshool's effects."

Source : Wikipedia