Itchy left nipple may be caused by impending menstruation, or it may be due to nipple eczema, dermatitis and other disease factors. 1. The onset of menstruation: the level of sex hormones in a woman’s body before the onset of menstruation will change drastically, nipple itching may occur, and some women may also experience swelling and pain in the breast area. 2. Dermatitis: The dermatitis may be caused by the left nipple, which is allergic to the material of clothes, air or some kind of substance. Itchy localized, may also be accompanied by erosion and redness and swelling. 3. Breast cancer: When breast cancer attacks, some patients will have blood, redness and swelling in the breast, and if they do not pay attention to local hygiene and are infected by bacteria, itching may also occur. There are many reasons that can cause itchy left nipple, and patients need to go to the hospital for breast examination to deal with the causes.