Water Pepper (Persicaria hydropiper), also known as smartweed, has a long history of use in traditional folk medicine across various cultures, particularly in East Asia and Europe. It has been applied topically or as a mouth rinse for various oral and mucosal ailments, including canker sores (aphthous ulcers). The rationale for its traditional use stems from its pungent, astringent qualities and the presence of bioactive compounds like polygodial, which have shown mild anti-inflammatory and antimicrobial effects in laboratory settings.

However, there is very limited scientific research directly evaluating Water Pepper’s efficacy for canker sores. Most references to its use are anecdotal or found in herbal compendia and ethnobotanical reports, rather than in controlled clinical trials or pharmacological studies. While some in vitro studies suggest that extracts of Water Pepper may inhibit the growth of certain bacteria and reduce inflammation, these results cannot be directly extrapolated to effectiveness in treating oral ulcers in humans.

In summary, the use of Water Pepper for supporting or treating canker sores is justified more by traditional practice than by scientific validation. The evidence base is weak and primarily historical or anecdotal, thus meriting a low evidence rating.