The best time for breast self-examination is one week after the end of menstruation because tissue changes before or during menstruation due to physiological engorgement of the breast, follicular hyperplasia and ductal expansion make breast tissue hypertrophy, which affects the effectiveness of the examination. If the menstrual cycle is irregular, it is better to perform self-examination at the same time of the month. A. Visual inspection Upright in front of the mirror to remove the top, in bright light, facing the mirror on both sides of the breast for visual examination, compare whether the bilateral breast symmetry, pay attention to the shape of the size and abnormal changes. The abnormal signs include: nipple overflow, nipple retraction, skin wrinkling, dimple sign, skin desquamation and abnormal changes in breast contour. The left upper limb is lifted and the three fingers of the right hand (index finger, middle finger and ring finger) are used to touch the breast slowly, steadily and carefully. Gradually move the left breast in a downward or reverse direction, at least three circles from the periphery of the breast to the nipple. An up-and-down or radial examination may also be performed, but care should be taken not to miss any areas. The axillary lymph nodes are also checked for enlargement. Finally, the nipple is gently squeezed between the thumb and index finger to observe for nipple drainage. If cloudy, yellowish or bloody fluid is found, the right breast should be examined immediately by the same method as above. Third, lying down check lying down check, to be detected upper limbs raised over the head on the pillow or folded towel pad to be detected under the shoulder. The purpose of this position is to make the breast flat and easy to check, and the method is the same as that of palpation. The earlier breast disease is detected, the greater the chance of cure. Monthly breast self-examination, if abnormalities are found, you should go to a specialist hospital for further professional examination in order to achieve early detection, early diagnosis and early treatment.