The use of apple cider vinegar (ACV) to treat or support diarrhea is rooted primarily in traditional and folk medicine rather than robust scientific validation. Historically, vinegar—including ACV—has been used in various cultures for digestive complaints, sometimes including diarrhea, with the rationale that its acidic nature could help "balance" the digestive tract or act as a mild antimicrobial agent. However, scientific studies specifically evaluating ACV for diarrhea in humans are lacking. Some laboratory research suggests that vinegar may possess antibacterial properties, which could theoretically help combat certain pathogens that cause diarrhea, but these findings have not been directly translated to clinical settings or tested in controlled trials for diarrhea treatment.

There is no consensus in modern medicine supporting ACV as a treatment for diarrhea, and major health organizations do not recommend it for this purpose. In some cases, ACV might even irritate the gut lining and potentially worsen symptoms, especially in sensitive individuals or when consumed in large quantities. Thus, while ACV’s use for diarrhea may persist in traditional or anecdotal contexts, the quality and quantity of supporting evidence are minimal, and its efficacy remains unproven.