Limited evidenceImmunity

Streptococcus Salivarius K12

An oral probiotic that colonises the throat and produces bacteriocins against Streptococcus pyogenes. Several trials report fewer sore throat and ear infection episodes, but almost all are small and poorly blinded.

Evidence last reviewed: August 2026

What the science says

Possible reduction in sore throat episodes Limited evidence
A systematic review of K12 for treating or preventing sore throat found studies suggesting reduced episodes of streptococcal pharyngitis, while judging the trials small, largely non-blinded and at substantial risk of bias. The reviewers concluded that better trials are needed before recommending it.
Ear and oral cavity outcomes Limited evidence
A systematic review of K12 in ear and oral health reported reductions in recurrent pharyngotonsillitis and acute otitis media across the available studies, again with methodological weaknesses throughout.
Paediatric prevention study Limited evidence
An open-label study in three-year-old children reported fewer episodes of streptococcal pharyngotonsillitis, scarlet fever and acute otitis media over a 90-day treatment plus follow-up. The lack of blinding and placebo control limits what can be concluded.

Dosage & safety

Studied doseOne lozenge providing roughly 1 billion CFU per day, dissolved slowly in the mouth after brushing teeth at night. Studied courses typically ran 30–90 days.

SafetyWell tolerated in the trials. Live-organism probiotics should be avoided by people who are severely immunocompromised, have central venous catheters or are at risk of endocarditis. Lozenges are a choking hazard for very young children — paediatric trials used age-appropriate formulations.

Scientific references

Effectiveness of the probiotic Streptococcus salivarius K12 for the treatment and/or prevention of sore throat: a systematic review
Wilcox CR, Stuart B, Leaver H, Lown M, Willcox M, Moore M, Little P — Clin Microbiol Infect, 2019
Influence of Oral Probiotic Streptococcus salivarius K12 on Ear and Oral Cavity Health in Humans: Systematic Review
Zupancic K, Kriksic V, Kovacevic I, Kovacevic D — Probiotics Antimicrob Proteins, 2017
Effect of administration of Streptococcus salivarius K12 on the occurrence of streptococcal pharyngo-tonsillitis, scarlet fever and acute otitis media in 3 years old children
Di Pierro F, Colombo M, Giuliani MG, Danza ML, Basile I, Bollani T, Conti AM, Zanvit A, Rottoli AS — Eur Rev Med Pharmacol Sci, 2016

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