Boric acid is supported by scientific evidence for use as an adjunctive therapy in certain types of vaginitis, particularly for recurrent or resistant vulvovaginal candidiasis (yeast infections) and trichomoniasis. It is not a first-line treatment, but clinical studies and guidelines endorse its use when standard antifungal or antiprotozoal treatments fail.

Several studies, including randomized controlled trials and case series, have shown that intravaginal boric acid capsules (typically 600 mg once daily for 14 days) can be effective in treating Candida glabrata and other non-albicans Candida infections, which are often resistant to conventional azole antifungals. The CDC’s 2021 Sexually Transmitted Infections Treatment Guidelines recommend boric acid as an option for azole-resistant vulvovaginal candidiasis and as adjunctive therapy for trichomoniasis in women with persistent symptoms after initial therapy.

The mechanism involves boric acid’s antifungal and antiseptic properties, likely through disruption of the fungal cell wall and alteration of vaginal pH. While boric acid is generally well tolerated, it is toxic if ingested orally and should not be used during pregnancy.

In summary, the use of boric acid for certain forms of vaginitis is scientifically validated, especially when conventional treatments are ineffective. However, more high-quality studies could further clarify its efficacy and safety profile.