Streptococcus salivarius K12
Also called BLIS K12, S. salivarius K12, K12 oral probiotic, oral probiotic K12, Bactoblis, OralBiotic.
Best grade C across 8 graded outcomes Other Last checked
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The short answer
From 12 sourcesStreptococcus salivarius K12 is an oral probiotic sold as lozenges for throat and mouth health. The largest trials were negative: no fewer ear infections in 827 day-care children or in 368 infants, and no fewer strep-positive sore throats in 1,314 schoolchildren. One trial in 160 people having head and neck radiotherapy found less severe mouth sores.
Quick pick
From a partner brand · paid link
NOW Foods OralBiotic (BLIS K12), 60 lozenges
from HerbsPro
Its name matches K12 lozenges and chewable tablets, one of the forms compared in our Forms table.
Label: 1 lozenge: 1 billion CFU BLIS K12 Streptococcus salivarius.
Contains milk.
Best for trying one bottle: $14.51 one-time (checked Oct 15, 2026).
Every graded outcome on this page
8 rows · line = participants- CGrade CStrep throat and tonsillitisSore throatn 1,846
- CGrade CSevere mouth sores (oral mucositis) during head and neck radiotherapyMouth sores during radiotherapyn 160
- CGrade CUpper respiratory infections in physically active young adultsColdsn 112
- DGrade DBad breath (volatile sulfur compounds)Bad breathn 80
- ∅No effectStrep-positive sore throats in schoolchildrenSore throatn 1,314
- ∅No effectEar infections needing antibiotics in day-care childrenEar infectionsn 827
- ∅No effectEar infections and respiratory infections in infantsEar infectionsn 368
- ∅No effectBad breath linked to tongue coatingBad breathn 28
- 5 more graded outcomes, in the evidence chapter
Key facts
- What it is
- A Streptococcus salivarius strain from the human mouth, delivered in lozenges that are sucked, not swallowed whole35
- Ear infections
- No reduction in two large trials: 8.2% vs 5.8% of day-care children needed antibiotics for ear infection over 6 months (827 children), and 37% vs 39% of infants dosed from 6 to 24 months had an ear infection (368 infants)210
- Sore throat
- Mixed: a review of 4 poor-quality trials found one positive and one null prevention trial; a 1,314-child school trial found no significant effect34
- Radiotherapy mouth sores
- Severe oral mucositis 36.6% vs 54.2% with placebo in 160 head and neck cancer patients5
- Safety
- 10 billion CFU a day for 28 days caused no blood or tolerance differences vs placebo in 53 adults (manufacturer-run study)6
- How long it stays
- Daily lozenges for 14 days kept K12 in the mouth of 59.1% of adults at day 14, but after dosing stopped it was found in only one person (from the weekly group) 1 to 3 weeks later12
What it is
Streptococcus salivarius K12 (BLIS K12) is an oral probiotic strain from the human mouth, sold as lozenges that dissolve slowly.
How it works
ProposedK12 is a normal mouth species; in children, saliva levels of S. salivarius rose after a month of K12 without disrupting the overall oral microbiome. Researchers propose it crowds out throat and mouth pathogens, but effects on otopathogens were uncertain.7
Forms
Form
| Form | Elemental % | Absorption (human data) | GI tolerance | Studied for |
|---|---|---|---|---|
| K12 lozenges and chewable tablets | Varies6Not applicable (dose in colony-forming units, CFU) | Not absorbed; colonises the mouth. Saliva levels of S. salivarius rose after 1 month of use in children. In adults, daily dosing kept colonisation higher than weekly dosing (85.7% vs 13.6% at day 7), and colonisation was lost after dosing stopped.712 | No differences in blood tests or adverse events vs placebo at 10 billion CFU a day for 28 days; well tolerated across the sore-throat trials.36 | Ear infections, sore throat, radiotherapy mouth sores, bad breath and colds |
What the human research says
Human trials only, one row per outcome. The form line shows what each trial actually tested. Grades follow our evidence-grading policy.
Trial map
8 graded outcomes, largest study first8 graded outcomes: 2 improved, 2 mixed, 4 no effect. The largest, a 2019 systematic review of 1,846 people on strep throat and tonsillitis, found mixed results. Outcomes that improved came from smaller studies: a median of 120 people, against 598 for no effect.
1Strep throat and tonsillitis
Mixed · Grade C · Systematic review, 1,846 people, 2019
Children and adults in 4 trials
Dose, result and source| Outcome | Found | People | Study | Who was studied |
|---|---|---|---|---|
| Strep throat and tonsillitis | Mixed | 1,846 | Grade C · Systematic review, 2019 | Children and adults in 4 trials |
| Strep-positive sore throats in schoolchildren | No effect | 1,314 | No-effect grade · RCT, 2018 | Children aged 5 to 14 at high risk of rheumatic fever (New Zealand) |
| Ear infections needing antibiotics in day-care children | No effect | 827 | No-effect grade · RCT, 2023 | Children aged 1 to 6 attending 50 day care centres (Oulu, Finland) |
| Ear infections and respiratory infections in infants | No effect | 368 | No-effect grade · RCT, 2026 | Infants from the general population (New Zealand), dosed from 6 to 24 months of age |
| Severe mouth sores (oral mucositis) during head and neck radiotherapy | Improved | 160 | Grade C · RCT, 2024 | Adults having radiotherapy for head and neck cancer (West China Hospital) |
| Upper respiratory infections in physically active young adults | Mixed | 112 | Grade C · RCT, 2024 | Physically active adults aged 19 to 25 (Italy) |
| Bad breath (volatile sulfur compounds) | Improved | 80 | Grade D · RCT, 2026 | Adults with halitosis (four groups: control, K12, tongue brushing, both) |
| Bad breath linked to tongue coating | No effect | 28 | No-effect grade · RCT, 2020 | Adults with tongue-coating halitosis who did not scrape the tongue or use antiseptic rinse first (Beijing) |
Every graded row
8 rowsShowing 8 of 8 outcomes. Human trials only.
CGrade CStrep throat and tonsillitisSore throatInconsistent; only unblinded trials were positiveSystematic review · 4 studies
n 1,846 · 2019
Mixed All 4 trials were rated poor quality. An unblinded trial in 222 young children reported fewer strep infections (16.2% vs 48.6%), but a placebo-controlled trial in 1,314 schoolchildren found no difference (7.8% vs 8.8%). In adults given K12 with penicillin there was no benefit. K12 was well tolerated.
- Design
- Systematic review, 4 studies, n = 1,846, 2019
- Population
- Children and adults in 4 trials
- Form
- K12 lozenges or products, daily
- Dose
- Daily K12 (doses varied by trial)
- Duration
- 3 months to four school terms
- Source
- Reference 3 · PubMed 30616011 (opens PubMed)
CGrade CSevere mouth sores (oral mucositis) during head and neck radiotherapyMouth sores during radiotherapyLess and shorter severe mucositis vs placeboRCT
n 160 · 2024
Improved Severe oral mucositis occurred in 36.6% with K12 vs 54.2% with placebo (P = .0351); mean duration 8.9 vs 18.3 days (P = .0084); hazard ratio for onset 0.55 (95% CI 0.34 to 0.89). Two people on K12 had mild or moderate flatulence or dyspepsia.
- Design
- RCT, n = 160, 2024
- Population
- Adults having radiotherapy for head and neck cancer (West China Hospital)
- Form
- K12 lozenges sucked three times a day
- Dose
- Three lozenges a day (CFU not stated in the abstract)
- Duration
- From the start to the end of radiotherapy
- Source
- Reference 5 · PubMed 38215354 (opens PubMed)
CGrade CUpper respiratory infections in physically active young adultsColdsNo overall difference; benefit only in a high-adherence subgroupRCT
n 112 · 2024
Mixed Overall symptom severity did not differ from placebo; participants with over 90% adherence to K12 reported more symptom-free days.
- Design
- RCT, n = 112, 2024
- Population
- Physically active adults aged 19 to 25 (Italy)
- Form
- K12 (Bactoblis)
- Dose
- One daily dose (CFU not stated in the abstract)
- Duration
- 4 months
- Source
- Reference 9 · PubMed 39597553 (opens PubMed)
DGrade DBad breath (volatile sulfur compounds)Bad breathSulfur compounds lower; odour score unchanged with K12 aloneRCT
n 80 · 2026
Improved Volatile sulfur compounds fell from baseline with K12, with tongue brushing and with both combined, most with the combination; organoleptic odour scores improved only in the combined group, and tongue coating did not fall with K12 alone.
- Design
- RCT, n = 80, 2026
- Population
- Adults with halitosis (four groups: control, K12, tongue brushing, both)
- Form
- K12 oral probiotic
- Dose
- Not stated in the abstract
- Duration
- 4 weeks, plus 4 weeks follow-up
- Source
- Reference 11 · PubMed 41604763 (opens PubMed)
∅No effectStrep-positive sore throats in schoolchildrenSore throatNo significant reductionRCT
n 1,314 · 2018
No effect 7.8% of swabs from the K12 group and 8.8% from the placebo group grew group A streptococcus, a nonsignificant 11.2% relative reduction.
- Design
- RCT, n = 1,314, 2018
- Population
- Children aged 5 to 14 at high risk of rheumatic fever (New Zealand)
- Form
- K12 lozenges, observed daily on school days
- Dose
- 2.5 billion CFU per lozenge
- Duration
- One school year
- Source
- Reference 4 · PubMed 29189607 (opens PubMed)
∅No effectEar infections needing antibiotics in day-care childrenEar infectionsNo fewer ear infections than placeboRCT
n 827 · 2023
No effect 34 children (8.2%) on K12 and 24 (5.8%) on placebo had at least one ear infection treated with antibiotics (relative risk 1.42, 95% CI 0.86 to 2.34; P = .17). Time to first episode did not differ.
- Design
- RCT, n = 827, 2023
- Population
- Children aged 1 to 6 attending 50 day care centres (Oulu, Finland)
- Form
- K12 oral powder (under 3) or chewable tablet (3 and over)
- Dose
- 1 billion CFU once daily in the evening
- Duration
- 6 months
- Source
- Reference 2 · PubMed 37917062 (opens PubMed)
∅No effectEar infections and respiratory infections in infantsEar infectionsNo fewer ear infections than placeboRCT
n 368 · 2026
No effect Doctor-recorded ear infections occurred in 37% on K12 and 39% on placebo (rate ratio 0.84, 95% CI 0.57 to 1.24); time to first episode, respiratory infections, antibiotic prescribing and healthcare use did not differ.
- Design
- RCT, n = 368, 2026
- Population
- Infants from the general population (New Zealand), dosed from 6 to 24 months of age
- Form
- K12 daily study product
- Dose
- Daily (amount not stated in the abstract)
- Duration
- 18 months (age 6 to 24 months)
- Source
- Reference 10 · PubMed 42693329 (opens PubMed)
∅No effectBad breath linked to tongue coatingBad breathNot better than placeboRCT
n 28 · 2020
No effect Odour scores and sulfur compounds fell from baseline in the K12 group, but there were no differences from placebo in odour, sulfur compounds or tongue coating.
- Design
- RCT, n = 28, 2020
- Population
- Adults with tongue-coating halitosis who did not scrape the tongue or use antiseptic rinse first (Beijing)
- Form
- K12 tablets sucked daily
- Dose
- One tablet a day (CFU not stated in the abstract)
- Duration
- 30 days
- Source
- Reference 8 · PubMed 32227309 (opens PubMed)
What the numbers add up to
Each point is worked out from the data and the sources numbered on this page, with the arithmetic shown under it. It adds no new data and is not medical advice.
The bigger the trial, the weaker the result
Strongest signal is outside everyday use
The clearest positive result is fewer severe mouth sores during head and neck radiotherapy, a single trial not yet repeated.5
Studied doses
Doses used in research, shown against the official limits. They describe the studies, not a recommendation for you.
Studied doses in research, not advice. These are amounts used in research, not personal advice. Your clinician or pharmacist can say what fits you.
Doses studied in human trials
Interactions and safety
Published interactions only: each row cites a source. No row means none was found in our sources, not that a combination is safe.
What Streptococcus salivarius K12 meets
2 cited rowsMedicines 2
Supplements and foods 0
No supplement rows in our sources.
- Reference summary
Choose a medicine or supplement above to read its cited rows here.
Also cited:
Antibiotics
ReviewReference summary
Antibiotics, for example Penicillin: In the one adult trial where K12 was given alongside penicillin for acute tonsillitis, it added no benefit. NCCIH says probiotics with antibiotics appear safe except in people who are very weak or immune-compromised.
Source 3, Clin Microbiol Infect (2019); Source 1, National Center for Complementary and Integrative Health (NCCIH) (2019)
Immunosuppressants
NIH fact sheetReference summary
Immunosuppressants: NCCIH says the risk of harmful effects from probiotics, such as infections, is greater in people with compromised immune systems; immune-suppressing medicines put people in that group.
Source 1, National Center for Complementary and Integrative Health (NCCIH) (2019)
Interactions
2 agents| Agent | What the source says | Evidence |
|---|---|---|
| Medicines2 | ||
| Antibioticse.g. Penicillin | In the one adult trial where K12 was given alongside penicillin for acute tonsillitis, it added no benefit. NCCIH says probiotics with antibiotics appear safe except in people who are very weak or immune-compromised.31 | Review |
| Immunosuppressants | NCCIH says the risk of harmful effects from probiotics, such as infections, is greater in people with compromised immune systems; immune-suppressing medicines put people in that group.1 | NIH fact sheet |
Check with what you take
Kept on this device onlyAdd what you take. We list every interaction our evidence profiles cite between Streptococcus salivarius K12 and your picks, and between your picks.
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Add a supplement or medicine you take to check it against Streptococcus salivarius K12.
Starting from one medicine? The interaction checker rates how serious each pair is, on a curated list of 19 entries for 11 medicines. This cabinet has no severity rating: it lists every interaction row our supplement pages cite.
Who should be careful
5 groups- Weakened immune system or serious illness
- NCCIH: the risk of harmful effects from probiotics is greater in people with severe illnesses or compromised immune systems.1
- Premature infants
- NCCIH reports that severe or fatal infections have occurred in premature infants given probiotics and that FDA has warned health care providers about this risk.1
- Pregnancy and breastfeeding
- We found no published safety data on K12 in pregnancy or breastfeeding, and no LactMed entry for this strain. NCCIH notes a general lack of solid information on how often probiotic side effects occur and how severe they are.1
- Instead of seeing a doctor
- NCCIH advises not using probiotics as a reason to postpone seeing a health care provider; a sore throat or ear pain may need assessment and treatment.1
- Taking antibiotics
- In the one adult trial where K12 was given alongside penicillin for acute tonsillitis, it added no benefit.3
How to read the label
What to check on the Supplement Facts panel.
How to read the label
3 checksCheck the strain
CFU per lozenge
Daily, not weekly
In a 2026 feasibility trial, K12 stayed in the mouth far more often with daily than with weekly lozenges (85.7% vs 13.6% at day 7) and was largely gone 1 to 3 weeks after stopping.12
Where to buy Streptococcus salivarius K12
Products from brands we partner with that contain Streptococcus salivarius K12. Check the amount per serving against the doses studied above, and the label for other ingredients.
Streptococcus salivarius K12 products from partner brands
1 product Paid links · we earn a commission- Quick pickHerbsProNOW Foods OralBiotic (BLIS K12), 60 lozenges
1 lozenge: 1 billion CFU BLIS K12 Streptococcus salivarius; contains milk; sweetened with xylitol and sorbitol
$14.51one-timeChecked Oct 15, 2026
Frequently asked questions
Short answers to common questions; the numbers link to the sources below.
Common questions
8 answersDoes K12 help with strep throat?
Does K12 fix bad breath?
Is K12 safe?
How long does K12 stay in the mouth?
Only while it is used. In a 2026 trial, daily lozenges for 14 days kept K12 in 59.1% of adults at day 14, but after stopping it was found in only one participant, from the weekly group, 1 to 3 weeks later.12
Can K12 be used with antibiotics?
Does BLIS K12 stop ear infections in children?
Is K12 safe in pregnancy or while breastfeeding?
We found no published safety data on K12 in pregnancy or breastfeeding. NCCIH notes that solid information on probiotic side effects is lacking in general.1
Sources
12 sources: trial abstracts, NIH fact sheets and reference databases. Numbers in the text link here.
Sources cited on this page
12 sources- 1Probiotics: Usefulness and SafetyFact sheet National Center for Complementary and Integrative Health (NCCIH), 2019 · nccih.nih.gov
- 2Streptococcus salivarius Probiotics to Prevent Acute Otitis Media in Children: A Randomized Clinical Trial.RCT JAMA Netw Open, 2023 · PMID 37917062
- 3Effectiveness of the probiotic Streptococcus salivarius K12 for the treatment and/or prevention of sore throat: a systematic review.Systematic review Clin Microbiol Infect, 2019 · PMID 30616011
- 4Effect of Oral Probiotic Streptococcus salivarius K12 on Group A Streptococcus Pharyngitis: A Pragmatic Trial in Schools.RCT Pediatr Infect Dis J, 2018 · PMID 29189607
- 5Streptococcus salivarius K12 Alleviates Oral Mucositis in Patients Undergoing Radiotherapy for Malignant Head and Neck Tumors: A Randomized Controlled Trial.RCT J Clin Oncol, 2024 · PMID 38215354
- 6Evaluation of safety and human tolerance of the oral probiotic Streptococcus salivarius K12: a randomized, placebo-controlled, double-blind study.RCT Food Chem Toxicol, 2011 · PMID 21722694
- 7Impact of Streptococcus salivarius K12 on Nasopharyngeal and Saliva Microbiome: A Randomized Controlled Trial.RCT Pediatr Infect Dis J, 2021 · PMID 33298762
- 8The Effect of Streptococcus salivarius K12 on Halitosis: a Double-Blind, Randomized, Placebo-Controlled Trial.RCT Probiotics Antimicrob Proteins, 2020 · PMID 32227309
- 9Efficacy of Streptococcus salivarius Blis K12 in the Prevention of Upper Respiratory Tract Infections in Physically Active Individuals: A Randomized Controlled Trial.RCT Microorganisms, 2024 · PMID 39597553
- 10Preventing otitis media and respiratory tract infections with the oral probiotic Streptococcus salivarius K12.RCT Eur J Pediatr, 2026 · PMID 42693329
- 11Tongue brushing and oral probiotics for the treatment of halitosis: a randomized controlled trial.RCT J Breath Res, 2026 · PMID 41604763
- 12BLIS study: a feasibility randomised controlled trial assessing compliance, acceptability and colonisation with different dosing regimens of the probiotic supplement Streptococcus salivarius K12 (Bactoblis) in adults in England.RCT BMJ Open, 2026 · PMID 42744363
What changed
Every dated change to this page: what changed, who made it and why.
Change log
2 entries| Date | Change | Who and why |
|---|---|---|
| evidence, summary, key facts, forms, studied doses, interactions, who should be careful, label guide, analysis, FAQ | Added a 368-infant ear-infection trial (PMID 42693329, no effect) and a 2026 bad-breath trial (41604763); a 2026 colonisation trial (42744363) now informs forms, key facts and the label guide. Added antibiotic and immune-suppression interactions and a pregnancy and breastfeeding note from NCCIH (no strain-specific data; no LactMed entry). A 2026 trial in children with ear effusion (PMID 41737842) was not graded because its abstract gives no participant count. Fact-checked against the sources; corrected: the bad-breath trial result now says sulfur compounds fell from baseline, and the colonisation follow-up notes the one remaining carrier was in the weekly group. | Writer: Kymata Health EditorialTrigger: A–Z page audit |
| all | Initial editorial evidence review. Every PMID checked against NCBI E-utilities esummary (title, year, journal; none retracted) and each cited abstract read; numbers taken from the abstracts. Funding: the safety study was run by BLIS Technologies (K12 maker); one author of the athlete trial advises the product's marketer; the other abstracts name no funder. Safety from NCCIH's Probiotics: Usefulness and Safety. Where to buy: NOW Foods OralBiotic (label checked 2026-10-15). | Writer: Kymata Health EditorialTrigger: new page |
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