The flexible areas on an infant’s head, commonly called soft spots, often worry new parents. These spots are a normal and necessary part of a baby’s anatomy, leading to questions about their function and when they disappear. Understanding the typical timeframe for closure can offer reassurance and help parents monitor their baby’s development.
Defining the Soft Spots
These flexible regions, scientifically known as fontanelles, are gaps where the skull bones have not yet fused. The baby’s skull is composed of multiple bony plates held together by flexible, fibrous joints called sutures. Fontanelles are the intersections where these sutures meet, creating membrane-covered openings.
The two most prominent soft spots are the anterior and posterior fontanelles, which differ in size and location. The anterior fontanelle is the larger, diamond-shaped spot located on the top, toward the front of the head. The smaller, triangular posterior fontanelle is situated at the back of the head. This flexibility is crucial for two primary purposes: it allows the skull plates to overlap slightly during passage through the birth canal, and it provides space for the rapid growth of the brain during infancy.
The Normal Timeline for Closure
The closure of the fontanelles is a process of ossification, where flexible tissue is replaced by bone, solidifying the skull. The posterior fontanelle, located at the back of the head, closes first. This smaller soft spot is typically sealed when the baby is between one and three months old, and sometimes it is already closed at birth.
The anterior fontanelle, the larger soft spot on top of the head, remains open longer to accommodate continued brain development. Its closure timing has a wide normal range, from nine months up to 24 months of age. Most commonly, this fontanelle closes when the child is 13 to 18 months old.
This variation in timing is a normal biological phenomenon and is not a cause for concern if the baby is otherwise developing typically. The fontanelle stays open long enough to protect the brain and allow for the significant growth that occurs during the first two years of life.
Warning Signs and What They Indicate
A healthy fontanelle should feel relatively flat and soft, or curve slightly inward, but changes in its appearance can signal a health issue.
A sunken fontanelle, which appears depressed below the surrounding skull, is often a sign of dehydration. This occurs if an infant is experiencing excessive fluid loss from vomiting or diarrhea, or not taking in enough fluids.
A bulging fontanelle is a more urgent concern, particularly if it persists when the baby is calm and sitting upright. While a normal fontanelle may temporarily bulge when a baby cries or strains, sustained outward swelling indicates increased pressure inside the skull. This increased intracranial pressure can signal serious conditions such as hydrocephalus, meningitis, or bleeding in the brain.
Parents should also monitor for soft spots that close too early or too late. Premature closure, known as craniosynostosis, occurs when skull sutures fuse before the brain finishes growing, potentially leading to an abnormally shaped head and restricted brain growth. Conversely, severely delayed closure beyond two years of age can be associated with underlying conditions, including congenital hypothyroidism, rickets, or certain genetic syndromes.
Any persistent bulging or significant sinking, especially if accompanied by symptoms like fever, excessive sleepiness, or irritability, warrants immediate medical attention.