Some bacteria make spores which can live for many years and then blossom and grow. Most probiotics do not make spores, so they gradually die off if they do not find a comfortable place to grow, meaning a moist, warm, friendly environment like the colon. However, when a probiotic sits on a shelf in a store, the bugs gradually die. The longer they are in a warehouse or on a store shelf the fewer live bacteria will be present. Refrigeration likely prolongs the life of probiotics but we don’t know for which ones and for how long. Most manufacturers will not tell you.