The question of when the human skull stops growing does not have a single answer because the skull is a complex structure made of two distinct parts that mature at different rates. The neurocranium, or braincase, is the bony shell that protects the brain. The viscerocranium forms the skeleton of the face.
These two components follow separate growth timelines. The neurocranium accommodates the rapid expansion of the brain in early childhood, leading to an early cessation of significant growth. The facial skeleton, however, continues to grow and remodel well into adolescence and early adulthood, meaning maturation is staggered and extends over many years.
Early Skull Development: The Closure of Fontanelles
The initial and most dramatic phase of skull growth occurs in infancy, centered on the neurocranium’s need to support the rapidly growing brain. At birth, the skull plates are separated by areas of dense, fibrous tissue called fontanelles, commonly known as soft spots. These open spaces serve two immediate purposes: they allow the skull bones to overlap during birth, and they permit the brain to undergo massive expansion during the first year of life.
The closure of these fontanelles is a visible marker of early skull development, occurring through intramembranous ossification, where fibrous tissue is converted directly into bone. The posterior fontanelle, located at the back of the head, is the first to close, typically fusing within the first two to three months after birth. The larger anterior fontanelle, found on the top-front of the head, remains open longer to accommodate the peak of early brain growth, usually closing between 7 and 19 months of age. By the time a child reaches two years old, the fontanelles have generally closed, marking the end of the skull’s most flexible and rapid growth period.
The Fusion of the Cranial Vault Sutures
Even after the fontanelles have closed, the large, flat bone plates of the neurocranium remain separated by narrow, fibrous joints known as cranial sutures. These sutures act as expansion joints, allowing for the slow but continued growth of the brain, which continues significantly until about age five. They permit the skull to expand perpendicular to the suture line, preventing restriction of brain development.
The process by which these sutures permanently fuse, known as synostosis, is gradual and spans many years, often extending into adulthood. While the skull’s protective function is established when brain growth slows, the anatomical closure of the major sutures occurs much later. For example, the sagittal suture may begin its final fusion in the late twenties. The coronal and lambdoid sutures can continue to fuse into the third or even fourth decade of life.
Extended Growth: Maturation of the Facial Skeleton
The final stage of skull maturation involves the viscerocranium, or facial skeleton, which continues its growth long after the braincase has stabilized. This delayed and extended growth accounts for the subtle changes in facial appearance that occur throughout adolescence and into early adulthood. Structures like the maxilla (upper jaw) and the mandible (lower jaw) grow and remodel through different mechanisms than the flat bones of the cranium.
The mandible, in particular, often continues to grow later than other facial bones due to its unique growth centers near the condyles. This mandibular growth spurt is associated with puberty, occurring around age 14 in males and age 11.5 in females. The bone continues to remodel for years afterward. Final skeletal maturity of the facial bones is often reached around age 15 for females, but may extend up to age 25 in males. The growth of the nasal structures and the expansion of the frontal sinuses also contribute to the changing shape of the face.