The causes of numbness of mouth after chemotherapy for breast cancer include drug-induced neurotoxic side effects, mucous membrane damage, allergic reactions, etc. 1. Breast cancer patients often choose chemotherapy drugs such as paclitaxel and doxorubicin, which can easily cause peripheral neurotoxicity, which is manifested as numbness of mouth, numbness of the endings of hands and feet and other symptoms. 2. Breast cancer patients often choose cyclophosphamide, fluorouracil and other chemotherapeutic drugs, these chemotherapeutic drugs are easy to cause mucous membrane damage, thus causing oral mucositis, which will also show symptoms such as numbness of the mouth and pain. 3. If patients are allergic to chemotherapy drugs, they can also show numbness of mouth.