Cheesemongers call it “Parm arm,” the itchy rash they sometimes get from breaking down a whole wheel of Parmigiano Reggiano. I’ve never had that experience, but Parmigiano Reggiano and some other aged cheeses can make my tongue burn. Ouch. It’s really unpleasant. And I’m not alone in this reaction. My husband never feels the burn, but others do, and last week I learned more about what causes it.

At the recent American Cheese Society conference, held virtually, presenter Pat Polowsky showed an image of a splotchy forearm next to a wedge of Parmigiano. Turns out it was his forearm. Polowsky works for Wisconsin’s Center for Dairy Research and publishes the Cheese Science Toolkit blog, but he has also spent time behind a retail counter in his occasional side hustle as a cheesemonger.

“It only happened that one time,” Polowsky says about his angry skin reaction. “It was from the sheer volume of Parm that I was handling.” But Polowsky, like me, also gets a burning sensation on his tongue from some cheeses—mostly well-aged, raw-milk wheels like the mountain cheeses of Switzerland.

The culprit is histamine, a naturally occurring compound found in many foods and beverages, including seafood, salumi, wine and beer. Microbes create histamine from histidine, an amino acid present in milk protein. They don’t always do it—the conditions have to be right—which is why some wedges of Parm and Gruyère make my tongue tingle and some don’t. Although I don’t enjoy the sensation, it’s momentary and not harmful, and histamines don’t seem to be present in any cheeses at levels that might cause more serious reactions, such as migraines. Even so, European regulators monitor histamine levels in cheese, and Swiss cheesemakers who make long-aged wheels are aware of this issue.

Some mongers tell me they wear long-sleeved shirts when cracking open a wheel of Parm. Others say they’ve learned to wash their arms immediately afterward. I asked Polowsky whether he thought taking a preventive antihistamine would help mongers avoid a reaction.

“That’s a big misconception,” he replied. “It’s not an allergic reaction. It’s a sensitivity that some people have more than others.”

Polowsky suspects we’re hearing more about these reactions because the cheeses with high histamine potential are often the ones discriminating consumers seek out. The more knowledgeable we get about cheese, the more we look for those well-aged artisan wheels made from raw milk. Cheesemakers can take steps to tamp down the activity of the microbes, says Polowsky, but some of those steps—like using pasteurized milk or selling younger wheels—would likely be ruled out of hand by many.

Personally, I’m willing to accept the occasional pain in return for the huge pleasure I get from aged cheese. And now, if I ever have the occasion to break down a whole wheel of Parmigiano Reggiano, I’ll know to roll down my sleeves.

For the science-inclined, here’s a deeper dive into the production of histamine in cheese.