Thyroid nodules may cause underarm swelling, but the incidence is low, or they may be caused by other reasons such as lipomas and sebaceous cysts. Thyroid nodule is a kind of confined lump in normal thyroid tissue, there are benign and malignant nodules, benign thyroid nodules usually do not cause underarm swelling, malignant thyroid nodules may occur axillary lymph node metastasis, resulting in underarm swelling, but the probability of occurrence is low. In addition, axillary swelling may also be caused by lipoma, sebaceous cysts, pathogenic bacteria invading the lymph nodes through the skin leading to lymph node enlargement, folliculitis and other disease factors. Patients with thyroid nodules who experience underarm swelling are advised to visit a hospital and ask the doctor to make a judgment and identify the cause.