The best time to check is 11 days after each menstrual period, which is the low tide of physiological changes in the breast. First, stand in front of a mirror, self-observe whether both breasts are of equal size and symmetrical shape, whether the nipple position is in the same plane, whether one nipple is receding, changing direction, whether there is local bulge, depression, whether there is micro erosion, abnormal discharge, whether there is blood in sweatshirt, shirt, etc. Next, lie flat on the bed, with the upper arm of the side being examined raised above the head and the back padded, and first use your fingers to feel for any lumps in the contralateral breast. Gently feel with fingers together on the palm surface, because the tactile sensation of fingertips is most sensitive when touched lightly, avoid heavy pressure, which can reduce the sensitivity of fingers and increase the chance of cancer metastasis. Firstly, use fingers to feel the inner part of the breast from top to bottom, then feel the outer part of the breast from bottom to top, especially note that the chance of cancer in the outer part is higher. The upper arm is then slightly lowered so that the caudal part of the breast is not stretched very far and is not missed during the examination. Then, the other finger will be used to feel the opposite breast in the same way.