“What is the relationship between dehydration and sunken anterior fontanelle?”

Dehydration is a loss of bodily fluids, it is similar to fluid volume depleting in a glass as the fluid evaporates and the fluid is not replenished. The fontanelle will depress or appear sunken as bodily fluids diminish.

Dehydration or malnutrition can cause a sunken fontanelle. Also, not all babies have a sunken fontanel when dehydrated. If this is observed with your child, you should call his/her pediatrician right away to investigate.

That is a sign of serious dehydration. Cerebrospinal fluid surrounds the brain. A fontanelle is an area where there is no skull bone between the brain and the skin. All bodily fluids contract in the face of dehydration, just like the volume of water in a glass decreases as water evaporates over time if not replenished. So the fontanelle will depress or appear sunken as bodily fluids diminish.

William Z. Cohen, M.D., FAAFP