What is Saccharomyces boulardii? Saccharomyces boulardii is a health promoting, probiotic yeast. To be an effective probiotic, microorganisms must have certain qualities to withstand the natural defense factors of the host. These include resistance to gastrointestinal transit and the ability to thrive at human core temperatures. Saccharomyces boulardii is a stomach acid-resistant probiotic, proven to survive high temperatures and transit into the intestines. As a probiotic, S. boulardii actively promotes healthy gastrointestinal flora, strengthens intestinal barrier function, and enhances immune function. This formulation is freeze-dried, lactose-free, and strain-verified through genetic typing to ensure maximum efficacy.