Streptococcus thermophilus

S. thermophilus

Snapshot

Indications	Contraindications
Infant acute diarrhea^{1, 2} Infant rotavirus shedding¹ H. pylori eradication adjunct³ Infant gut microbiota⁴	Milk allergy⁵ Compromised immune system⁵

Streptococcus thermophilus is a lactic acid bacterium used as a yogurt starter culture and included in many probiotic products, usually alongside other strains. It acts through lactic acid fermentation and effects on the gut microbiota.² Supplementation is used to prevent acute diarrhea in infants, typically with Bifidobacterium formulas. One hospital trial reduced incidence, while a larger community trial reduced severity but not incidence^{1, 2}.

A later trial in healthy infants found a fermented formula did not change diarrhea incidence but made episodes less severe². In adults, adding Lactobacillus delbrueckii and S. thermophilus to triple therapy improved H. pylori eradication in a randomized trial³. A 2020 review found most intervention studies did not identify S. thermophilus in stool accurately enough to distinguish it from Streptococcus salivarius, leaving gut survival uncertain⁶. Over one thousand products list S. thermophilus, mostly as powders and capsules in multistrain blends; see Form comparison.

The most practical caution is allergenic: some United States (US) labels note cultures grown on milk-based media⁵. US product labels also direct patients taking immune-suppressing medications, or with compromised immunity, to consult a physician first⁵.

Last updated October 17, 2026. Read how we make monographs.

In the full monograph

25 sources, 16 studies

When to useThe situations practitioners use it for, each with the reason and the study behind it.
SafetyWho should avoid it, who needs extra care, and the side effects reported in studies.
InteractionsThe medicines and supplements it interacts with, the effect of each, and what labeling says to watch.
Protocol notesThe doses used in studies, how and when they were taken, and how the forms on the market compare.
How it worksWhat it is and how it works in the body, in plain terms.
Published studiesThe studies behind each use, popular claims checked against them, and trials still under way.
Word of mouthWhat patients and practitioners report online, kept separate from the clinical evidence.
Clinical perspectiveA closing read of where the evidence is solid, where it is thin, and what has not been studied.

Snapshot

In the full monograph

Sources