Pyrrosia, a genus of ferns commonly known as “shi wei” in traditional Chinese medicine (TCM), has a long history of use in East Asian herbal practices. According to TCM, Pyrrosia leaf is categorized as a “cooling” herb and is often used to clear heat and promote urination, as well as to address mouth sores, including canker sores (aphthous ulcers).

The traditional rationale is based on the TCM theory that mouth ulcers are often caused by “heat” in the heart or stomach meridians, and Pyrrosia is believed to clear this pathogenic heat, thereby reducing symptoms. Classical texts such as the “Ben Cao Gang Mu” (Compendium of Materia Medica) mention its use for oral ulcers and sore throats. Pyrrosia is frequently included in compound formulas for oral ulcers or mouth inflammation.

However, modern scientific evidence supporting the efficacy of Pyrrosia specifically for canker sores is limited. There are few clinical studies or pharmacological investigations directly examining Pyrrosia’s effect on aphthous ulcers. Its traditional use remains the primary basis for its application in this context, and the overall evidence level is best described as modest and lacking rigorous clinical validation. In summary, Pyrrosia’s role in canker sore treatment is rooted in historical and traditional practice rather than supported by contemporary scientific research.