Streptococcus salivarius is a commensal bacterium commonly found in the human oral cavity and upper respiratory tract. Its use to support the mucus membranes—specifically those of the mouth, throat, and nasopharynx—has a basis in scientific research. S. salivarius strains, particularly K12 and M18, have been studied for their potential probiotic properties. These strains have demonstrated the ability to colonize the oral mucosa and produce bacteriocins that inhibit the growth of pathogenic bacteria such as Streptococcus pyogenes (a common cause of pharyngitis) and Streptococcus pneumoniae.

Several clinical trials have shown that S. salivarius K12 supplementation reduces the incidence and duration of streptococcal pharyngitis and other upper respiratory tract infections in children and adults. The proposed mechanism involves competitive exclusion of pathogens and enhancement of mucosal immune responses, thereby supporting the health of oral and pharyngeal mucous membranes. However, most studies focus on the oral and pharyngeal regions, with less evidence available for other mucus membranes in the body.

Overall, the scientific evidence is moderate (rated 3/5), and supports the use of S. salivarius for maintaining healthy oral and pharyngeal mucous membranes. Its use for broader mucus membrane support throughout the body is less substantiated.