The phenomenon of residual milk after 5 years of weaning is related to incomplete emptying of milk, medication, mammary duct dilatation, hypothyroidism and so on. 1. Incomplete emptying of breast milk: For some people who have not completely emptied their breast milk after breastfeeding, there may be a small amount of milk stagnation in the breast milk, which may lead to the phenomenon of residual milk after 5 years of weaning. 2. medication: if women take drugs that can inhibit or deplete dopamine receptors, increase estrogen levels, etc., may lead to abnormal serum prolactin secretion, thus causing residual milk after weaning for five years. 3. Dilatation of mammary ducts: this disease may cause some patients to have residual milk for 5 years after weaning. The cause of the disease is not yet clear, and it may be related to the obstruction of drainage of mammary ducts, abnormal hormone levels, etc. It is also easy to be accompanied by other symptoms such as skin redness and swelling, and enlarged axillary lymph nodes. 4. Hypothyroidism: The disease is related to destruction of the thyroid gland, iodine excess or deficiency. Common manifestations of patients include fear of cold and less sweat, weight gain, slow movement, breast milk overflow, etc. It can also be manifested in the form of residual milk after 5 years of weaning. It is recommended that patients with residual milk after 5 years of weaning should consult a doctor immediately so that the cause of the disease can be clarified and treated according to the doctor’s instructions.