Probiotics

What are probiotics?

Updated 4 Nov 2026

Short answer

Probiotics are live microorganisms that give a health benefit when taken in adequate amounts.[1][2] Most are bacteria, and some are yeasts. They are found in some fermented foods such as yogurt, are added to other foods and are sold as supplements.[1]

Probiotics are not one substance. Each one is a specific strain, named by genus, species and a strain code, as in Lacticaseibacillus rhamnosus GG.[1] If one kind of Lactobacillus helps prevent an illness, that does not necessarily mean that another kind will do the same.[3] In 2020, scientists split the old genus Lactobacillus into 25 genera, so some strains now have new names.[4]

Prebiotics are something else: they are carbohydrates that gut microbes use as fuel. Synbiotics contain both prebiotics and probiotics. Postbiotics are made of dead or broken microbes.[1]

Sources (4)

  1. Probiotics: Fact Sheet for Health Professionals. NIH Office of Dietary Supplements, 2025. ods.od.nih.gov
  2. Expert consensus document. The International Scientific Association for Probiotics and Prebiotics consensus statement on the scope and appropriate use of the term probiotic. Hill C, Guarner F, Reid G, Gibson GR, Merenstein DJ, Pot B, et al. Nat Rev Gastroenterol Hepatol, 2014. PMID 24912386
  3. Probiotics: Usefulness and Safety. NIH National Center for Complementary and Integrative Health, 2019. www.nccih.nih.gov
  4. A taxonomic note on the genus Lactobacillus: Description of 23 novel genera, emended description of the genus Lactobacillus Beijerinck 1901, and union of Lactobacillaceae and Leuconostocaceae. Zheng J, Wittouck S, Salvetti E, Franz CMAP, Harris HMB, Mattarelli P, et al. Int J Syst Evol Microbiol, 2020. PMID 32293557

More about probiotics

Do probiotics change your gut bacteria?Is a higher CFU count better?Which foods contain probiotics?What are probiotics used for?Do probiotics prevent diarrhea from antibiotics and C. difficile?Are probiotics safe, and who should avoid them?

For education; not medical advice. Talk to a doctor before you start, stop or change a supplement.