Breasts will get smaller and smaller may be due to malnutrition, excessive exercise, pancreatitis and biliary obstruction, excessive pressure on the breasts, and atrophy of the mammary glands. 1. Malnutrition: too little intake of nutrients, especially meat, eggs and milk containing a lot of lipids and proteins; prolonged diarrhea, indigestion and other causes of insufficient absorption of nutrients, resulting in poor breast development, and thus the breasts will become smaller and smaller. 2. Excessive exercise: prolonged overload exercise leads to an increase in energy consumption in the body tissues, the body fat tissue, including fat tissue in the mammary glands is consumed in large quantities, so the breasts will become smaller and smaller. 3. Pancreatitis and bile duct obstruction: chronic pancreatitis leads to pancreatic fluid secretion disorder, lipase deficiency; bile duct obstruction leads to bile acid excretion disorder, fat and other nutrients digestion disorder, breast fat tissue lack of supply, and breasts will become smaller and smaller. 4. Excessive pressure on the breasts: excessive pressure on the breasts caused by long-term breast corset, wearing too tight bra, sleeping in prone position, etc. may also lead to smaller and smaller breasts. 5. Mammary gland atrophy: estrogen has the function of promoting the development of mammary gland ducts, progesterone has the function of promoting the development of mammary gland follicles, when the ovary declines, the synthesis of estrogen and progesterone is insufficient, resulting in the atrophy of mammary glands, and thus the breasts will become smaller and smaller. The breasts will become smaller and smaller may be related to a variety of factors, it is recommended to consult a doctor for a clear diagnosis.