Saccharomyces boulardii is a tropical yeast first isolated from lychee and mangosteen peels in 1923 by French scientist Henri Boulard.

Although early reports claimed distinct taxonomic, metabolic, and genetic properties,[1] S. boulardii is a grouping of S. cerevisiae strains, all sharing a >99% genomic relatedness.

[9] Boulard first isolated this yeast after he observed natives of Southeast Asia chewing on the skin of lychee and mangosteen in an attempt to control the symptoms of cholera.

S. boulardii encodes extra copies of yeast adhesion proteins called flocculins that help to stick to pathogenic bacteria and stop them from binding to the intestinal mucus.[2]: supp.

[15][16] A 2015 meta-analysis of 21 randomised controlled trials (4780 participants) confirmed that S. boulardii is effective in reducing the risk of AAD in children and adults.

[19] S. boulardii has been shown to significantly increase the recovery rate of stage IV AIDS patients with diarrhea versus placebo.

[22][23] A position paper published by ESPGHAN Working Group for Probiotics and Prebiotics based on a systematic reviews and randomized controlled trials suggested that S. boulardii (low quality of evidence, strong recommendation) may be considered in the management of children with acute gastroenteritis in addition to rehydration therapy.

[25] It can be also used for baking, where its ability to deter bacteria translates into inhibition of rope spoilage, a bread defect caused by Bacillus subtilis or B. licheniformis contamination.