For centuries, folklore suggested that fermented dairy products containing live active cultures are healthful. Recent controlled scientific investigation supports these traditional views, suggesting that probiotics are a valuable part of a healthy diet. In addition, the emergence of some new public health risks suggests an important role for effective probiotics in the mitigation of illness. For example, the ability of probiotic bacteria to support the immune system could be important to the elderly or other people with compromised immune function. (It is important that immune compromised individuals ask their doctor before taking any dietary supplement, including probiotics.)

Infections are another area with potential for probiotics. Some infections, once thought self-limiting or readily treatable with antibiotics, are now recognized as more serious health threats. Bacterial vaginosis used to be considered just an annoyance. Now we know it is associated with low birth weight infants and increased risk of sexually transmitted diseases. New foodborne pathogens have emerged as prevalent and life threatening, including Shiga-like Escherichia coli strains. Multiple antibiotic resistances are a continual threat in the battle against once-treatable infections. And in non-industrialized nations, infections such as rotavirus claim the lives of hundreds of thousands of infants yearly. Prevention of infections before they occur is clearly the better alternative. Certain probiotics may be a safe, cost-effective approach that adds a barrier against microbial infection.