Although your baby's skull is soft and delicate, it is designed to protect him during birth and help his expanding brain develop. Unlike an adult brain, an infant's skull has joints that don't close up until later in childhood. This slow skull development is important for your child's healthy growth.
In the womb, your baby's body is prepared for birth. An infant's skull is made up of six bones held together by large flexible joints or sutures. A newborn baby's head is larger than his body and those sutures allow the skull bones to overlap and compress as it passes through the birth canal. According to the website for the Embryology Department at the University of New South Wales, after birth the stretchy sutures allow your baby's skull to expand to house the rapidly growing brain. Over time, these sutures slowly harden and fuse, making the skull one single bone.
Holding a baby requires delicately supporting his head and neck, and you'll notice two soft areas on the top of the head that seem to gaps in the bony skull. The larger soft spot on the top is called the anterior fontanel and the smaller, less noticeable spot on the back is the posterior fontanel, according to HealthyChildren.org. MayoClinic.com notes that these soft spots are well protected and also help to accommodate your infant's developing brain.
Infant skulls develop slowly because the brain continues to grow after birth and will not reach adult size until about the age of 7 years, according to the University of New South Wales website. The sutures or joints between the skull bones begin to fuse together during the first two years of life. The two soft fontanel spots also become smaller, closing completely by the time your child is about 3 years old.
The suture joints and fontanels are vitally important for the healthy growth and development of your baby's brain. If one of these spots hardens and closes early, it can lead to a severe birth defect called craniosynostosis. The National Institute of Neurological Disorders and Strokes explains that craniosynostosis occurs when one or more spots on the skull become hard and immoveable before they should, preventing the growing brain from expanding and impeding brain development. An infant with this birth defect might need surgery to reopen the fused area, relieve the pressure and give the brain room to grow.
The joints in your baby's skull make it easier for him to pass through the birth canal, however it can cause the shape of a baby's head to become molded unevenly during birth. This post-birth lopsided skull usually evens out on its own. MayoClinic.com warns that a baby's soft skull might also change shape if he lies on one side too long. Although it is safest for your baby to sleep on his back, putting him on his side during the day when you can watch him closely will help to prevent positional molding.