From the weird world of celebrities comes word that actress Kate Beckinsale travels with Kerrygold grass-fed butter.

“I find it quite hard to get ahold of,” Beckinsale says. “If I’m going from one city to another, I’ll put some in my suitcase to make sure I have it. I’m the crazy person traveling with butter.”

This raises a major question: Is that safe?

It’s a little tricky, Darin Detwiler, PhD, director of the Regulatory Affairs of Food and Food Industries program at Northeastern University, tells Yahoo Lifestyle. “Butter is interesting because there is dairy in it, but it’s mostly fat,” he says. “And fat doesn’t exactly help bacterial growth.”

But there are a few things that can happen if you don’t refrigerate your butter, especially if you keep it out for a long period of time or don’t refrigerate it at all, Detwiler says. One is that it can go rancid. “You’ll know right away,” he says. Another is that you can get foodborne bacteria like E. coli or salmonella, which can grow on the butter and infect you. Finally, if you leave your butter out, there’s more of a chance for cross contamination with other foods and bacteria that may be in your kitchen. “The more you leave it out, the more you’re leaving it open to cross-contamination or the bacterial growth,” Detwiler says. “You really have to take that into consideration.”