Itchy bottom during menstruation may be caused by vulvovaginitis, vaginitis, allergy and other factors. 1. Vulvovaginitis: not paying attention to the hygiene of the lower body during menstruation may induce vulvovaginitis, due to the irritation of inflammatory substances, which will lead to itching underneath, manifested as vulvar itching, vulvar redness, and in severe cases, may also cause urethritis and other urinary tract infections. 2. Vaginitis: Due to the presence of bad dew during menstruation, if you don’t pay attention to perineal cleansing, vaginitis may occur, which may lead to itching underneath. 3. Allergy: During menstruation, the use of poorly treated sanitary napkins or irritating bathing products may cause allergic reactions in the vulva, leading to itching underneath, which may be accompanied by redness and tingling. If the symptoms of itching are more obvious during menstruation, it is recommended to consult a doctor for examination and treatment to avoid delaying the condition.