Timing of self-examination: Mammography is best performed a week after the end of the menstrual period, for women with a 28-day menstrual cycle just between the two periods. Because the volume of the breast is minimal at this time and the physiological breast swelling has basically subsided, it is easier to detect subtle abnormalities in the breast and to determine the quality of the lesion more accurately. Scope of self-examination: Bilateral breasts, including the bilateral armpits and the upper and lower clavicle fossa. Self-examination method: When performing a breast examination, face the mirror, preferably with your shirt off, arms crossed, and under good lighting conditions. One look: the size of bilateral breasts, the vast majority of normal women have differences in the size of bilateral breasts, but if there is a difference in the recent past, or if the original difference has changed significantly in a short period of time, the possibility of breast lesions should be considered. The second look: skin color, a common skin change is flushing; the third look: nipples, whether there is nipple invagination or skewed. It is important to develop the habit of sequential examination when palpating and not to miss out. The right side of the breast should be palpated with the left hand and the right hand should be used to fix the breast if necessary. The opposite is true for the right hand. The middle three fingers are brought together, the metacarpophalangeal joints are slightly bent, and the end fingers are placed flat on the breast for touch. The touching fingers should push the breast skin in the response area to do a small range of pressure, and the strength of each small area touched should be from light to heavy. Do not use the entire hand to grasp and pinch the breast or armpit. Finally, squeeze the nipple with moderate force to see if there is nipple discharge. Self-examination of the breast is the most convenient and economical method of examination. It is also recommended for all women because it is non-invasive, reproducible and universal. However, self-examination of the breast has its limitations. Some diseases, especially early lesions, cannot be detected by mere visual inspection and palpation, and need to be examined by physical examination equipment. The correctness and proficiency of self-examination methods will affect the effectiveness of self-examination. Therefore, self-examination cannot replace medical examination by a specialist. In addition to the need to go to a specialist for further examination when abnormalities are found during self-examination, normal women should undergo a clinical breast examination by a doctor every three years starting from the age of 20. From the age of 35, regular breast examinations should be done every year.