Why do some probiotics need to be refrigerated?

You’ve probably heard that probiotic supplements can be a major power player when it comes to achieving and maintaining healthy gut bacteria. (Hello, better digestion, clearer skin, lifted moods, and more.)

But when it comes to choosing one that actually works for you, the options can get overwhelming. Strains and doses vary, and to make matters more confusing, some are found in a refrigerator while others seem just fine on the shelf—what’s that all about?

Here’s the deal. “Many probiotic bacteria are naturally sensitive to heat and moisture,” explains Patricia Bannan, MS, RDN, author of Eat Right When Time is Tight. This is particularly problematic if you live in a warm or humid environment. “Heat can kill organisms, and moisture can activate them within pills, only to die due to lack of nutrients and a proper environment.” And while it probably won’t hurt you to eat “dead” probiotics, you also won’t get any of the benefits you’re after.

This doesn’t mean all probiotics on a shelf are worthless, though. “Ideally, the difference is that the manufacturer of a probiotic that doesn’t need to be refrigerated is using technology that allows the probiotic to remain stable and stay alive at room temperature,” explains Mary Ellen Sanders, PhD, probiotic consultant with Dairy & Food Culture Technologies in Centennial, CO. “Probiotics that contain freeze-dried organisms and are in packaging to prevent moisture, such as blister packs, generally do not need refrigeration,” adds Bannan.

Just make sure that once you remove a shelf-stable probiotic from its container or blister pack, you use it right away, Bannan says—don’t put it into a weekly pill container, for example. And make sure your supplement has been tested for efficacy, to ensure it actually does everything it promises.

But are refrigerated probiotics better than the ones on the shelf?

So, to shop the refrigerated section or the shelf?  One isn’t necessarily better than the other, though there may be a more limited number of strains that are available at room temperature, suggests Sanders. (Though that depends on the manufacturer.)

The bottom line is to follow the supplement’s instructions. If you’re not sure, refrigeration is a safe bet, says Bannan. “The most important thing is that the probiotics remain viable in the gut,” she adds. And as long as you’re storing them the way they’re meant to be, you’re halfway there.

Here are the exact strains of probiotics you should be taking, based on your wellness needs. And if you feel like your supplement of choice isn’t working, these could be the reasons you’re not seeing results.