Large and small breasts are mainly related to genetic factors, but also to the degree of obesity, hormone levels, and whether or not you are pregnant and breastfeeding. The main components of the breast are fatty tissue, mammary glandular tissue and connective tissue, and it is mainly the mammary glandular tissue and fatty tissue that affect the size. When a person’s body fat content is high, the fat content of the breasts will increase accordingly, resulting in larger breasts than others or when they are thin, but they will also decrease in size when they lose weight. Changes in hormone levels in the body can also cause changes in breast size. When puberty occurs, sex hormone levels in the body increase and breasts begin to develop and will be larger than before. During pregnancy and lactation, the progesterone and lactogen in the body increase, and the breasts will increase accordingly. After menopause, when the hormone level in a woman’s body decreases, the breast gland atrophies, and the breast will then become smaller accordingly.