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Why does big red gum wrappers burn your skin?
Question Date: 2006-05-31
Answer 1:

Thank you for sending such an interesting question! You may be surprised to hear that a related question captured the interest of scientists working at the Scripps Institute in San Diego. Who would have thought that chewing gum would be so thought provoking?!

Actually, Big Red chewing gum, Atomic Fire Balls (my personal favorite), and some types of toothpastes and mouthwashes all produce the same kind of burning sensation that you describe (though most people usually experience this sensation in their mouths). Do you have any idea what ingredient is shared by all of these products?

The answer lies in the bark of evergreen trees that are native to Sri Lanka, a tiny island just off the coast of India. Certain portions of their bark are dried, ground into a fine powder and used as a spice that you probably know as cinnamon. Other parts of the bark are used to extract oil. For the trees, this oil prevents them from being invaded and damaged by fungi. For people, the oil is used to flavor a variety of products, including chewing gum and Atomic Fire Balls (did I mention that these are my personal favorite?). The main ingredient of the oil -- and the one that produces a burning sensation -- is called cinnamic aldehyde. Because powdered cinnamon contains very small amounts of cinnamic aldehyde, it usually doesn't give your mouth or skin a burning sensation. On the other hand, cinnamon oil contains amounts of cinnamic aldehyde large enough to cause the burning sensation that you experienced.

So how can the cinnamic aldehyde in Big Red chewing gum make your mouth and skin feel like they're on fire (after all, chewing gum is certainly not hot to the touch)? This is precisely the kind of question that scientists at the Scripps Institute are trying to unravel. Our ability to perceive temperature -- say, when we put our hand close to a hot stove or when we grab an ice cube tray, is controlled by nerve cells responsible for sensing hot and cold. These nerve cells have endings embedded very close to the surface of our skin (and also inside the linings of our mouth). When we encounter something in our environment that is hot, specialized sensor molecules on the nerve endings are activated. Once activated, a "hot" signal is transmitted through our spinal cords and eventually into our brains.

As you probably guessed, other sensor molecules are "tuned" to respond to cold temperatures and allow our brains to perceive certain things in our environment as "cold". Oddly enough, certain compounds, like the cinnamic aldehyde in Big Red chewing gum, activate the same kinds of nerve sensors that detect cold! Why then do we perceive a burning sensation when we contact the cinnamic aldehyde contained in these types of products. It seems that these same cold receptors also convey sensations of pain that our brains sometimes mistake for heat. Case in point: Some unfortunate Artic travelers experience such extremes in cold that that report the sensation of burning pain. Apparently cinnamic aldehyde works the same way.

Some people are more sensitive to cinnamic aldehyde than others. Your chewing gum wrapper probably contained some cinnamic aldehyde that contacted your skin, activated your cold sensors, and made you feel a burning sensation! Blame it on our brains!

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