I admit it, I was completely wrong. But I have an excuse: I was misled by published articles. For years I have written that the sensitivity in the mouth for capsaicin was controlled by the number of taste buds, and that super-tasters, people with a higher concentration of taste buds, couldn’t take the hot stuff as well as the non-tasters, who had a genetically-linked lesser number of them in their mouths. Sometime in 2002, I received an email from a reader telling me I was wrong and that taste buds could only detect sour, sweet, bitter, salty, and umami flavors. (Umami is the flavor of monosodium glutamate, or MSG.) He wrote that capsaicin is not detected by the taste buds because it does not fall into any of those five categories. This person promised to forward links to prove me wrong, but he never did, so I forgot about it.
Illustration by Lois Lyles
But in May, 2003, the proof was, well, in the spicy pudding. Scientists Elizabeth D. Prescott and David Julius of the University of California, San Francisco, announced they had identified a lipid molecule called PIP2 that plays a crucial role in controlling the strength of the burning sensation caused by capsaicin. A lipid molecule is a fatty molecule, insoluble in water, but soluble in fat solvents and alcohol–just like capsaicin. In the mouth, there is a capsaicin receptor called TRPV1 and the lipid molecule PIP2 is bound to it. In the presence of capsaicin, the PIP2 molecule separates from the receptor, causing a painful sensation. Here’s the scientific description: “In this process, the capsaicin receptor (TRPV1) is sensitized by phosphatidylinositol-4,5-bisphosphate (PIP2) hydrolysis following phospholipase C activation.” That’s quite a mouthful.
Now, what governs the degree of pain? The strength of the binding of the molecule to the receptor, say the scientists–the stronger the binding, the more powerful the pain sensation when the capsaicin causes the separation. And what determines the strength of the binding? To quote the researchers: “Thus, modification of this PIP2 regulatory domain by genetic, biochemical, or pharmacological mechanisms may have profound effects on sensitivity of primary afferent nerve fibers to chemical and thermal stimuli under normal or pathological conditions.”
Now I’m no scientist, but it seems to me that they are saying that the sensitivity to capsaicin is determined by genetics–some people’s lipid molecules have a stronger bond with the capsaicin receptors than others. But by stating that biochemical and pharmacological mechanisms can also play a role, this could explain why some people become desensitized to capsaicin and can take more and more heat.
I’m certain that further study will reveal even more information regarding this process, so stay tuned. And by the way, if you are worried about capsaicin destroying your five to ten thousand taste buds, you should know that all of them are replaced every two weeks, anyway. So forget about your taste buds and concentrate on the binding of your lipid molecules!