A new systematic review finds promising signals for lactoferrin and probiotics—but the evidence is still too limited to call either an established treatment.
Black stain can be one of those frustrating paediatric dental findings that looks far more dramatic than the underlying clinical problem. The dark pigmentation is usually seen as a series of black lines or dots along the cervical margins of teeth, and although it is generally an extrinsic chromogenic stain rather than conventional caries, it can be persistent, recurrent and cosmetically concerning.
For clinicians, the bigger question is often what happens after the stain is professionally removed.
Could something be done to reduce its recurrence?
A 2026 systematic review published in the Oral Health Journal has looked specifically at two proposed approaches—lactoferrin and probiotics. The findings are interesting, but they also illustrate how easily a promising biological mechanism can get ahead of the clinical evidence.
Why lactoferrin?
Lactoferrin is a naturally occurring glycoprotein found in milk and other biological fluids. One of its important biological properties is its ability to bind iron.
That is relevant because iron availability has been implicated in the formation of black stain. By sequestering iron, lactoferrin may make the oral environment less favourable for microorganisms associated with chromogenic staining.
The review describes lactoferrin as having several additional biological properties, including antimicrobial, anti-biofilm, anti-adhesive and anti-inflammatory effects.
But does that translate into less black stain clinically?
The evidence is still thin.
One of the studies included in the review was an observational study in which patients received lactoferrin tablets containing 50 mg lactoferrin and 50 mg D-biotin, twice daily for 90 days after oral hygiene treatment. The authors reported that lactoferrin could help counteract black stain, supporting the hypothesis that salivary iron availability may be involved in its formation.
That is biologically plausible, but an observational study cannot establish that lactoferrin itself caused the improvement.
What about probiotics?
The probiotic argument is somewhat different.
Rather than targeting iron availability, probiotics aim to influence the oral microbial environment. The review examined evidence involving strains including Streptococcus salivarius M18 and Lactobacillus reuteri Prodentis.
An in-vitro study found that both probiotics could inhibit microorganisms associated with black stain, with S. salivarius M18 showing greater antimicrobial activity than L. reuteri in the tested conditions. The effect was also dose-dependent.
But in-vitro antimicrobial activity is not the same as clinical stain prevention.
The more clinically interesting evidence came from a randomized study involving 58 children aged 4–10 years with black stain.
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