Capsaicin (8-methyl-N-vanillyl-trans-6-nonenamide; FEMA# 3404, CAS# 404-86-4) occurs in the Capsicum species. It has a mild, warm-herbaceous odor, with very pungent taste, and it is applied for its pungent taste in meaty and spicy formulations.
Capsaicin is at the head of a list of capsaicinoids, all having high Scoville heat unit values (F-2). As a comparison, piperine has only 100,000 Scoville heat units.
The capsaicin transient receptor potential (TRP) TRPV1 is the principal transduction channel for nociception. Excessive TRPV1 activation causes pathological pain. Capsaicin selectively binds to a protein known as TRPV1, which resides on the membranes of pain- and heat-sensing neurons. TRPV1 is a heat-activated calcium channel, which opens between 37–45°C. When capsaicin binds to TRPV1, it causes the channel to open below 37°C, which is why capsaicin is linked to the sensation of heat. Prolonged activation of these neurons by capsaicin depletes presynaptic substance P, one of the body’s neurotransmitters for pain and heat. Neurons that do not contain TRPV1 are unaffected.