Vietnamese sophora (Sophora flavescens), also known as "Khổ sâm" in Vietnamese, has a long history of use in traditional medicine throughout East Asia. In Vietnamese and Chinese herbal practices, extracts from the root have been used topically to address various skin conditions, including dandruff, eczema, and other forms of dermatitis. The rationale for its use in dandruff is largely based on its recognized antibacterial and antifungal properties in traditional medicine, which are believed to help reduce scalp irritation and control excessive shedding of skin.

However, there is little direct scientific evidence specifically supporting the efficacy of Vietnamese sophora for dandruff treatment. While some in vitro studies have demonstrated antimicrobial activity of Sophora flavescens extracts against certain skin pathogens, including Malassezia species (the yeast often implicated in dandruff), these findings have not been robustly confirmed in clinical trials for dandruff. Most evidence remains anecdotal or based on traditional use rather than rigorous scientific validation.

In summary, the use of Vietnamese sophora to support or treat dandruff is primarily justified by traditional practice, with only limited indirect scientific rationale but no high-quality clinical evidence as of now.