There are many reasons why hyperthyroidism may occur during breastfeeding. First of all, hyperthyroidism may occur during breastfeeding because women are breastfeeding, the hormone fluctuation in the body is larger, the hormone fluctuation in the body is easy to lead to certain thyroxine abnormality in the body, which causes the body to develop hyperthyroidism. Secondly, breastfeeding due to the care of the baby, may cause breastfeeding women lack of sleep, stress, which will cause the human body hormone fluctuations abnormal, resulting in the human body hyperthyroidism symptoms. In addition, breastfeeding is prone to hyperthyroidism, may also be due to the intake of excessive iodine content of food, such as kelp, seafood, sea fish, etc., these foods are likely to lead to the rise of iodine in the human body, thus causing the human body to secrete too much thyroid stimulating hormone, the body out of the thyroid hormone is too prone to trigger the human body to develop hyperthyroidism.