If you make a batch of caramel apples this Halloween or buy some at the orchard watch out because they might try to kill you.

Suspicion about these delicious treats came when last year seven people died from a Listeria outbreak which turned out was caused by caramel apples! Since the outbreak the University of Wisconsin has been studying caramel apples to try to figure out the reason they're good breeding grounds for bacteria.

They found that just because you dip an apple in hot caramel doesn't mean it kills all the bacteria on its skin. The caramel actually adds a nice insulated layer for bacteria to grow and multiply.

Home made are especially dangerous because the apples aren't treated like store bought. They are ok when eaten right away but It's especially bad if the apples are kept refrigerated for a long time after they're made.

Scientists found if you wash your apples really well before you dip them in caramel, and then eat them within a few days, you'll probably be safe from Listeria. They hit the danger zone once they sit for weeks or longer.