Candidal vaginitis is caused by an overgrowth of Candida yeast in the vagina. It is more common in women who are pregnant, taking oral contraceptives or corticosteroids, have diabetes or HIV/AIDS, or have poor personal hygiene. Diagnosis involves examining vaginal discharge for characteristics like being white, flaky, or curd-like, as well as testing the discharge using potassium hydroxide or culturing it to identify Candida. Treatment focuses on improving hygiene, discontinuing medications that could cause infection, controlling diabetes, and using antifungal creams, pessaries, or oral medications like fluconazole for 7-14 days.