A baby’s soft spot, medically termed a fontanelle, is a gap in the skull where the bone plates have not yet fused together. These spaces are covered by a tough, protective membrane that separates the scalp from the underlying brain tissue. Fontanelles are a normal feature of infant development, serving a specific biological purpose during the first years of life. Understanding these areas helps parents recognize signs of normal growth and when to seek guidance from a healthcare provider.
Anatomy and Essential Functions
The skull of a newborn is composed of several separate bony plates joined by flexible seams called sutures. Fontanelles are the wider intersections where these sutures meet, creating membranous gaps that allow for movement. This unique structure is necessary for two fundamental biological processes that occur around the time of birth and throughout early infancy.
The first function allows the skull bones to temporarily overlap and compress, a process known as molding, as the baby passes through the narrow birth canal during delivery. This flexibility helps reduce the overall size of the head, facilitating a safer passage. The skull typically returns to its normal shape within a few days after birth.
The second function is to accommodate the rapid expansion of the brain, which nearly triples in size during the first year of life. The open fontanelles and flexible sutures provide the necessary space for the brain to grow without being constrained by a rigid bone casing.
The Different Soft Spots and When They Close
The two most prominent fontanelles are the anterior and posterior. The posterior fontanelle is the smaller, triangular-shaped soft spot located toward the back of the head. It is typically small at birth and often closes within the first two to three months of life.
The anterior fontanelle is the larger, diamond-shaped soft spot found on the top of the head. Located between the frontal and parietal bones, its closure occurs much later than the posterior fontanelle, usually between 9 and 18 months of age.
The time frame for the anterior fontanelle’s closure can vary significantly, with some closing as early as seven months and others remaining open up to 24 months. Healthcare providers routinely monitor the size and tension of both fontanelles during checkups to ensure the skull is developing appropriately.
Safe Handling and Warning Signs
The fontanelles are protected by a durable membrane, so gentle touching, washing the baby’s hair, or using a soft brush will not cause harm. There is no need to avoid contact with the soft spot itself. A common observation is a slight, rhythmic pulsing of the fontanelle, which reflects the baby’s heartbeat and blood flow through the brain’s vessels.
The physical appearance of the fontanelle indicates the baby’s health status. A bulging fontanelle, particularly when the baby is calm and upright, can signal increased pressure inside the skull, potentially associated with fluid buildup or infection. If the fontanelle bulges when the baby is crying or coughing, it is a normal response to temporary pressure and should flatten once the baby is relaxed.
Conversely, a fontanelle that appears significantly sunken may indicate dehydration, often alongside signs like a lack of wet diapers or dry mouth. Both a persistently sunken or bulging fontanelle require immediate medical evaluation. Premature closure of the soft spots, known as craniosynostosis, can restrict brain growth and development, necessitating prompt attention.