Bregma is the bone gap formed by the poorly jointed skull of infants and children. There are anterior fontanelle and posterior fontanelle. The anterior fontanelle is located in the anterior parietal area and is diamond-shaped, closing at about 12 to 18 months after birth, while the posterior fontanelle is located in the occipital area and is triangular-shaped, closing at about 2 to 4 months after birth. The sunken fontanelle is mainly related to the change of intracranial pressure, when the intracranial pressure decreases, the sunken fontanelle will appear. Generally speaking, the main reason for the sunken fontanelle of babies is dehydration, usually the child feeds with less water or vomits for a long time, diarrhea causes the sunken fontanelle due to the decrease of intracranial pressure. Generally speaking, there is no need to worry too much about minor sunken fontanelle, just give your child enough water to ensure the supply of nutrition, and the fontanelle will return to normal after about 1-3 days. If the fontanelle is sunken for a long time and there is an obvious protrusion of bones around it, it is necessary to consider the possibility of calcium deficiency, which will not only affect the sunken fontanelle but also the closing of the fontanelle. In short, don’t be too nervous about the sunken fontanelle of your baby, give your child water in time, and if it doesn’t improve after three days of water supplementation, go to the hospital in time to check if there is calcium deficiency.