Probiotics are microorganisms that are believed to provide health benefits when consumed. The term probiotic is currently used to name ingested microorganisms associated with beneficial effects to humans and other animals. Introduction of the concept is generally attributed to Nobel Prize recipient Élie Metchnikoff, who in 1907 suggested that “the dependence of the intestinal microbes on the food makes it possible to adopt measures to modify the flora in our bodies and to replace the harmful microbes by useful microbes”. A significant expansion of the potential market for probiotics has led to higher requirements for scientific substantiation of putative beneficial effects conferred by the microorganisms. Studies on the medical benefits of probiotics have yet to reveal a cause-effect relationship, and their medical effectiveness has yet to be conclusively proven for most of the studies conducted thus far. Commonly claimed benefits of probiotics include the decrease of potentially pathogenic gastro-intestinal microorganisms; the reduction of gastro-intestinal discomfort; the strengthening of the immune system; the improvement of the skin’s function; the improvement of bowel regularity; the strengthening of the resistance to cedar pollen allergens; the decrease in body pathogens; the reduction of flatulence and bloating; the protection of DNA; the protection of proteins and lipids from oxidative damage; and the maintaining of individual intestinal microbiota in subjects receiving antibiotic treatment. Scientific evidence to date has been insufficient to substantiate any anti-disease claims or health benefits from consuming probiotics.