New research found that this classic treat could make you sick if it's not stored in the refrigerator.
Caramel coated apples
Credit: Brent Hofacker/Shutterstock

Caramel candy apples: Yum! Listeria monocytogenes: Yuck!

A new study has found that this fall favorite could potentially make you ill if not refrigerated.

The research, which was published online in mBio, compared caramel-coated Granny smith apples kept at room temperature or in the refrigerator. Some apples had dipping sticks, some did not.

Researchers from the University of Wisconsin-Madison's Food Research Institute found that listeria grew rapidly on unrefrigerated caramel apples with sticks. The average population of listera on these apples increased 1,000-fold compared to those without sticks also stored at room temperature.

On the other hand, refrigeration of these dipped apples substantially decreased the growth of listeria. Refrigerated apples without sticks had no listeria growth after four weeks.

Consuming listeria can cause listeriosis. Symptoms of listeriosis (headache, stiff neck, and fever) often do not appear until three or four weeks after eating infected foods.

"Dipping the apples in hot caramel killed off a lot of the surface bacteria," said study author Kathleen Glass, Ph.D., in a press release. "But those that still survived were the ones that were able to grow. If someone ate those apples fresh, they probably would not get sick. But because caramel-dipped apples are typically set out at room temperature for multiple days, maybe up to two weeks, it is enough time for the bacteria to grow."

Glass also noted that her team decided to conduct this study due to the listeriosis outbreak in 2014 that killed seven people and prompted three companies to voluntarily recall their pre-packaged caramel apples.

Moral of the story: If you're making your own caramel candy apples, you'll want to refrigerate the ones you don't eat right away. If you're buying them, make sure to ask when the apples were made and whether or not they've been refrigerated during that time. And if the house down the block leaves them out for trick-or-treaters? You might want to think twice before grabbing one.

Caitlin St John is an Editorial Assistant for who splits her time between New York City and her hometown on Long Island. Follow her on Twitter: @CAITYstjohn.