The “soft spot” on a baby’s head is medically known as a fontanelle, representing natural gaps in the skull bones of infants. These areas are a normal part of development, allowing the newborn skull to be flexible for birth and to accommodate the rapid growth of the brain immediately following delivery. Understanding the fontanelles’ structure and function provides clear guidance for their safe handling and monitoring.
The Anatomy and Purpose of Fontanelles
The infant skull is not a single, solid bone but rather a collection of separate bony plates connected by fibrous joints called sutures. Where several of these sutures meet, a wider, membrane-covered space remains, forming a fontanelle.
The largest is the diamond-shaped anterior fontanelle, located on the top-front of the head. A smaller, triangular-shaped posterior fontanelle exists near the back of the head. These spaces allow the skull bones to temporarily overlap, a process called molding, which compresses the head for easier passage through the narrow birth canal during labor.
Following birth, the fontanelles accommodate the rapid growth of the brain, which nearly doubles in size during the first year of life. The flexible, unfused plates provide the necessary room for this expansion without creating pressure on the brain tissue.
Safe Handling and Daily Care
The brain is protected by a tough, fibrous membrane beneath the skin that covers the gap in the bone. This membrane is strong enough to withstand the gentle pressures of everyday routine. Standard, supportive handling of the infant’s head is completely safe and will not cause harm to the fontanelle area.
Routine activities like bathing and drying the baby’s hair can be performed normally with a soft cloth or gentle washing action. Lightly washing and gently massaging the scalp is helpful for preventing the buildup of flakes associated with cradle cap. Caregivers should avoid applying any direct, sharp pressure, such as using a pointed object or pressing forcefully into the spot.
Recognizing Normal and Abnormal Appearance
A normal fontanelle should feel soft to the touch and appear flat or slightly curved inward when the baby is calm and upright. It is common for the fontanelle to visibly pulse in sync with the baby’s heartbeat, which is a reflection of blood flow and pressure within the underlying brain tissue. This pulsation is a normal physiological sign.
The fontanelle’s appearance is a valuable indicator of an infant’s overall health and hydration status. A fontanelle that appears significantly sunken or depressed, sitting noticeably below the surrounding skull bones, is a sign of severe dehydration. This condition usually results from insufficient fluid intake or excessive fluid loss and requires immediate medical consultation.
Conversely, a bulging or tense fontanelle, which curves noticeably outward when the baby is calm, signals an increase in pressure inside the skull. While the fontanelle may temporarily bulge when the baby is crying or straining, a persistent bulge can indicate a serious issue such as hydrocephalus or meningitis. If the fontanelle remains tense and bulging, especially when accompanied by fever or extreme drowsiness, emergency medical attention is necessary.
The Timeline for Fontanelle Closure
The fontanelles close through ossification, where fibrous tissue is replaced by bone. The two main fontanelles close on separate timelines, monitored during routine check-ups. The smaller posterior fontanelle typically closes first, with the bony plates fusing within the first two to three months after birth.
The anterior fontanelle, the larger soft spot, remains open longer to accommodate early brain growth. This fontanelle generally closes between seven and 18 months of age. Closure that happens much earlier than expected may be a sign of craniosynostosis, where the skull bones fuse prematurely, potentially restricting brain growth. Conversely, a significantly delayed closure can be associated with underlying conditions like metabolic disorders or hypothyroidism.