What Happens to a Baby's Soft Spot as They Grow?

At birth, an infant’s skull has separate bone plates that are not yet fused together to allow for rapid brain growth during the first one to two years of life. The spaces between the skull bones are the “fontanelles” or “soft spots.” As the baby grows and develops, you will notice the soft spots changing.

Soft Spots at Birth

Newborns have two soft spots -- one in the front at the top of the head and the other in the back near the crown of the head. During birth, a baby’s head must mold and compress to fit through the tight birth canal. The separate skull plates enable the baby’s head to fit safely and effectively. Sometimes a newborn’s head might be misshapen due to the compression during the birth, but this is a temporary condition. Within a week or two at most, the skull bones will move back and the head will have a more standard appearance.

Anterior and Posterior Fontanelles

The anterior soft spot sits front and center on a baby’s skull. Depending on how much hair your baby has, the soft spot may be very obvious or it could hide almost completely under hair. The anterior soft spot generally closes completely by about 18 to 24 months of age. The soft spot at the back of your baby’s head -- the posterior fontanelle -- may be more difficult to locate than the front soft spot due to its smaller size 1. This soft spot typically closes completely by the time the infant reaches 3 to 6 months of age. With both soft spots, the skull bones slowly shift and move until they fuse together over the fontanelles.

Normal Fontanel Characteristics

You may notice a baby’s soft spot pulsating sometimes. Although the fontanelle won’t always pulsate, when it does there is no cause for alarm. The rate of pulses in the fontanelle corresponds directly to your baby’s heart rate. Although a soft spot can seem fragile, it’s stronger than it appears. The fibrous layer over the baby’s head is strong enough to withstand normal hair washing, brushing and touching.

Special Concerns

The soft spots can be symptomatic of other health issues or illnesses. If a baby is ill with a fever or virus, a sunken soft spot can help diagnose dehydration. Assess the baby for other dehydration symptoms, including dry diapers, vomiting and diarrhea. Call a physician if you think your baby may be dehydrated. Fontanelles closing too early can also create significant health issues for a baby, according to the Columbia University Medical Center 3. Without the initial gap in the skull bones present to allow the brain to grow and expand, the skull may become deformed from the pressure of the growing brain. Corrective surgery may be necessary to resolve the problem.