Menstrual cup and its use. For some people, there's a chance the silicone or rubber material can cause an allergic reaction. It may cause vaginal irritation. A menstrual cup may irritate your vagina if the cup isn't cleaned and cared for properly. It may also cause discomfort if you insert the cup without any lubrication. If your cup is restricting urine and not allowing you to fully empty your bladder this may contribute to a uti in some instances.