The “soft spot” on a baby’s head, known anatomically as a fontanelle, is a normal and necessary feature of early development. It is an adaptive design allowing the infant skull to manage the rigors of birth and the rapid growth that follows. Understanding the function and expected timeline of these soft areas can provide reassurance and clarify when to seek medical advice. Pediatricians monitor this natural closure process during routine check-ups.
Defining the Fontanelles and Their Purpose
A fontanelle is a soft, membrane-covered space where the bony plates of the skull have not yet fused together. The infant skull is comprised of several plates joined by flexible joints called sutures, and fontanelles occur at the junction points of these sutures. Newborns typically have several fontanelles, but the two most prominent are the anterior and posterior fontanelles.
The anterior fontanelle is the larger, diamond-shaped soft spot located on the top front of the head. The posterior fontanelle is much smaller, triangular, and situated toward the back of the head. These openings serve two primary functions in the first year of life.
First, they allow the skull plates to overlap slightly, a process called molding, which enables the baby’s head to navigate the narrow birth canal during delivery. Second, the fontanelles and flexible sutures accommodate the remarkable growth of the brain. These gaps ensure that the expanding brain is not restricted, as it grows faster than the surrounding bone in infancy.
The Typical Timeline for Soft Spot Closure
The soft spots close at different times as the process of ossification takes place. The posterior fontanelle typically closes much earlier than the anterior one. This small, triangular spot at the back of the head usually closes within the first two to three months after birth.
The large anterior fontanelle is the last to close and is the one parents monitor the longest. Closure of this diamond-shaped area typically occurs over a wide range of time, reflecting normal variation in infant development. The expected range for anterior fontanelle closure is generally between 7 months and 18 months of age, though some variation up to 24 months is considered normal. This lengthy window allows for the significant brain growth that occurs throughout a baby’s first year.
The average closure time for the anterior fontanelle is often cited around 12 to 14 months, but the timing is highly individualized. Pediatricians routinely check the size and tension of this fontanelle during well-child visits. If the soft spot is still open past the two-year mark, a medical evaluation may be warranted to rule out certain underlying conditions.
When to Seek Medical Attention
A normal fontanelle should feel relatively flat and soft, perhaps curving slightly inward. It may also show a slight pulsation, which is harmless and simply reflects the baby’s heartbeat and blood flow in the brain’s vessels. Parents should seek immediate medical attention if the fontanelle appears significantly sunken or noticeably bulging, as these changes can signal a health issue.
A significantly sunken fontanelle is most often a sign of dehydration, which can quickly become serious in infants. This may be accompanied by other signs like fewer wet diapers, dry mouth, or lethargy, and requires prompt fluid management. Conversely, a tense or bulging fontanelle, especially when the baby is calm and upright, suggests increased pressure inside the skull. This condition can be a symptom of a serious issue like hydrocephalus, meningitis, or intracranial bleeding, and requires emergency care.
Concerns also arise when the closure timing falls significantly outside the normal range. If the anterior fontanelle closes too early, typically before six months, it may raise suspicion for craniosynostosis, a condition where the skull bones prematurely fuse, potentially restricting brain growth. Delayed closure, or a fontanelle that remains open past two years, may indicate underlying issues such as hypothyroidism, Down syndrome, or certain bone disorders, all of which warrant further testing and monitoring by a healthcare provider.