California rose (Rosa californica) has a history of traditional use by some Native American groups for various ailments, including as a mouthwash or poultice for oral issues such as canker sores. The petals and leaves have been used in folk medicine preparations due to their perceived soothing and mild astringent properties, which could theoretically help with minor oral irritations. However, this use is primarily based on ethnobotanical records rather than modern clinical research.

To date, there is no significant scientific validation—such as in vitro studies, animal models, or clinical trials—demonstrating the efficacy of California rose specifically for treating canker sores (aphthous ulcers). There is limited general evidence that rose species contain tannins and other compounds with mild anti-inflammatory or antimicrobial effects, but these findings have not been translated into direct support for California rose in this context. Thus, the use of California rose for canker sores is justified by tradition, and the scientific evidence is minimal or anecdotal at best.

In summary, California rose’s use for canker sores is supported by traditional practices rather than rigorous scientific evaluation, and the current evidence rating is low.