Probiotics are live microorganisms, usually bacteria or yeast, that, when consumed in adequate amounts, can benefit health by influencing the gut microbiome. Most research focuses on strains of Lactobacillus, Bifidobacterium and Saccharomyces.

Evidence is strongest for a few specific uses. Certain probiotic strains can help prevent or shorten infectious diarrhea, particularly in children, and may reduce antibiotic associated diarrhea by restoring microbial balance. Some strains also appear to modestly reduce symptoms of irritable bowel syndrome, such as bloating and abdominal pain, although results vary between products.

There is emerging evidence that probiotics might support management of inflammatory bowel diseases like ulcerative colitis by helping maintain remission, but they are not a replacement for standard treatments. In allergy and atopic disease, some studies suggest that giving probiotics to pregnant women, breastfeeding mothers or infants may slightly reduce the risk of eczema, though findings are inconsistent.

Beyond the gut, research explores whether probiotics can influence immune responses, metabolic health and even mood, through the gut brain axis. A few small trials report improvements in anxiety or depressive symptoms, but results are preliminary and often strain specific.

Overall, benefits depend highly on the exact strain, dose and duration used. Many commercial products have not been tested in rigorous trials, and quality control is variable. Probiotics are generally safe for healthy people but can pose risks for those who are critically ill or immunocompromised. Current evidence supports targeted use for specific conditions, while broader claims remain unproven and require larger, well controlled studies.