The health of our oral flora has far-reaching effects: from caries prevention to gum health to fresh breath. In recent years, it has become increasingly clear that the key is not just "killing" germs – but rather the targeted development of a healthy microbial balance.
Probiotics for oral care are therefore becoming increasingly popular. However, not every bacterial strain found in probiotic preparations is actually suitable for the oral cavity. On the contrary: Many products contain beneficial strains for the gut but are ineffective in the oral cavity.
In this article, you will learn what requirements a probiotic must meet to be effective in oral care – and why ultimately only two strains really meet these requirements: Streptococcus salivarius M18 and K12 .
What makes an effective probiotic for the mouth?
For a probiotic bacterial strain to actually have a positive effect on your oral health, it must meet certain criteria:
1. It must occur naturally in the mouth
Only microorganisms that are already part of the healthy oral flora can settle there sustainably and interact with other bacteria.
2. It must be able to settle in the oral cavity
Many probiotic bacteria—such as Lactobacillus or Bifidobacterium —originate from the intestinal environment. They don't survive long enough in the oral cavity or lack "docking sites" on teeth, mucous membranes, or the tongue.
3. It must show positive effects on oral health
Truly suitable oral probiotics inhibit pathogenic bacteria, reduce the risk of tooth decay and gum disease, support the saliva pH value and promote the natural balance in the biofilm of the teeth.
Streptococcus salivarius M18 & K12 – The two effective oral probiotics
Current research and clinical studies clearly show that only two strains reliably meet these requirements:
✅ Streptococcus salivarius M18
This strain preferentially colonizes tooth surfaces and mucous membranes. It is effective against caries-causing bacteria such as Streptococcus mutans , producing so-called bacteriocins (antibacterial proteins) and enzymes that break down plaque and stabilize the pH. Studies show that M18 can significantly reduce the risk of caries, plaque, and gingivitis .
✅ Streptococcus salivarius K12
Active primarily in the throat, K12 also produces bacteriocins, but is particularly effective against germs that cause bad breath, sore throats, and recurring throat infections . K12 is therefore ideal for people with chronic tonsillitis, tonsil problems, or bad breath.
Both strains are considered to be particularly safe , well tolerated and are usually offered as lozenges – ideal for settlement in the mouth.
Comparison table: Probiotic strains for oral care
| Probiotic strain | Settlement in the oral cavity | Scientifically proven | Effective for |
|---|---|---|---|
| Streptococcus salivarius M18 | ✅ Yes | ✅ Yes | Caries, plaque, gingivitis |
| Streptococcus salivarius K12 | ✅ Yes | ✅ Yes | Bad breath, sore throat, throat infections |
| Lactobacillus rhamnosus | ❌ No | 🔶 Partially | Effective in the intestines, not long-term active in the mouth |
| Bifidobacterium lactis | ❌ No | 🔶 Partially | Useful in the intestine, not suitable for oral flora |
| Lactobacillus reuteri | 🔶 Short-term | 🔶 Little data | In rare cases temporarily active in the mouth |
Why other probiotics are not suitable for oral care
Many commercially available probiotics target the gut—and that's a good thing. But the mouth has a completely different microbial environment that requires special adaptations.
Lactobacilli and bifidobacteria often only survive briefly in the oral cavity and do not offer lasting effects. They do not adhere to dental or mucous membrane structures and cannot defeat established oral germs. Therefore, products containing exclusively these strains offer no benefit for oral health —even if they contain high-quality ingredients.
How to use M18 and K12 correctly
For optimal effectiveness, probiotic strains should be applied regularly and locally in the mouth —preferably in the form of lozenges, sprays, or soluble strips. Ideally, this should be done after brushing, when the tooth surfaces are clean and receptive.
A typical course of treatment lasts between 30 days and 3 months – depending on the goal (e.g. bad breath, caries prevention or support after taking antibiotics in the ear, nose and throat area).
Conclusion: For a healthy oral flora there are only two really suitable probiotics
The science is clear: When it comes to targeted support of the oral flora , Streptococcus salivarius M18 and K12 are the only strains with proven effectiveness.
They promote a healthy microbial balance, displace pathogenic bacteria, and thus sustainably strengthen teeth, gums, and throat. Other probiotic strains from intestinal supplements are simply unsuitable for this purpose.
Anyone who wants to supplement their oral care holistically should rely on these two oral probiotic superheroes – natural, effective and well-tolerated.
