Dear Eloise,
My work as a science cat has introduced me to human foods—like chips and salsa. I love the spicy taste of salsa, but I always keep a saucer of milk handy.
I talked about why milk calms the spicy feeling with my friend Emily Cukier. She’s a chemistry librarian at Washington State University.
She told me that the spicy feeling comes from something called capsaicin. The amount of capsaicin in a pepper determines how hot it is.
When you bite a hot pepper, little bits of capsaicin stick to special proteins that sit on the nerve cells on your tongue. The proteins are called receptors.
“When capsaicin binds to its receptor, the receptor opens up and tells the nerve cell to fire,” Cukier said. “That sends a signal to your brain where it’s interpreted as heat and irritation.”
One way to stop the spicy feeling is to unstick the bits of capsaicin from the receptors. But capsaicin doesn’t mix well with water. No matter how much water you chug after eating hot peppers, the water will just slosh over the receptors. It won’t wash away the capsaicin.
But milk has two things water doesn’t have: fats and a protein called casein. That protein attracts capsaicin like catnip. If the protein is around, the bits of capsaicin will hop off the receptors. The protein forms globs around the capsaicin. It’s like how soap forms globs around dirt and grease when you wash your hands. Then, the protein and fats in milk work together to wash away the capsaicin.
Once all the capsaicin has left your receptors, the “spicy” signal to your brain stops.
Cukier told me that another way to deal with the spicy feeling is to eat dry, rough foods. Like crackers or chips.
“Those foods will produce different sensations in your mouth that can distract your brain from the spiciness,” Cukier said. “That why they’re often served with spicy foods.”
Like my chips and salsa.
So, why don’t we just avoid foods that hurt? It turns out the spicy signal also causes your brain to release endorphins—sometimes called “happy hormones.” They’re the same chemical signals your brain releases when you play or hug someone you love.
So, capsaicin can make us feel good at the same time it makes us feel a little bad.
Eating lots of spicy food could make you less sensitive to it, too. Over time, your tongue can adjust to having lots of capsaicin around. The nerve cells slurp in some of the receptors so they’re no longer poking out of the cells. That means there are fewer places for capsaicin to stick—and less of that spicy feeling.
Maybe that’s why, after years of living and eating with humans, salsa makes me pep-purrr.
Sincerely,
Dr. Universe