The sunken fontanel of the baby is considered to be related to dehydration, malnutrition, chronic wasting disease or physiological phenomenon. 1. Dehydration, if the baby is seriously dehydrated may lead to the loss of body fluids, the body’s water content decreases, may lead to fontanel depression. 2. Malnutrition, usually if you don’t pay attention to the baby’s diet, often partial food, picky eating, malnutrition, body wasting may appear after the baby fontanel concave down symptoms. 3. Chronic consumptive diseases, clinical malnutrition, repeated illness, various malignant tumors and other chronic consumptive diseases may lead to the body overburdened, energy consumption is too fast, so this symptom will appear. 4. Physiological phenomenon: fontanel is composed of the connection of bones, especially when the fontanel is relatively large, there may be a slight depression, if the child does not have the influence of disease, generally speaking, not a big problem. Baby fontanel concave may also have other reasons, it is recommended to go to the hospital in time to improve the examination to clarify the cause of the disease, to give targeted treatment or treatment.