Fontanelles, the soft spots on a baby’s head, are a normal feature of infant anatomy. While they are resilient and rarely require special attention, their appearance offers important clues about a baby’s health. Understanding the difference between a normal appearance and a sign of trouble is important for every caregiver. Recognizing specific changes in the fontanelles helps you know when to simply observe and when to seek immediate medical advice.
The Function and Normal Appearance of Soft Spots
Fontanelles are spaces between the bony plates of the skull that have not yet fused together. A newborn has two primary soft spots: the large, diamond-shaped anterior fontanelle on top of the head and the smaller, triangle-shaped posterior fontanelle toward the back. These gaps are protected by tough membranes, allowing the skull to be flexible.
The function of the fontanelles is two-fold, serving both the birth process and early development. During labor, they allow the bony plates to overlap, reducing the head’s circumference to facilitate passage through the birth canal. After birth, this flexibility accommodates the rapid growth of the brain, which nearly triples in size during the first year of life.
A healthy fontanelle should appear flat or slightly curved inward when the baby is calm and upright. It is normal to see a gentle, rhythmic pulsing in the anterior fontanelle, which mirrors the baby’s heartbeat. The spot may bulge slightly when the baby cries, strains, or vomits, but it must return to a flat or slightly concave appearance once the baby is settled.
When to Worry: Signs of Increased Pressure (Bulging)
A fontanelle that is truly bulging or tense is a sign that pressure is rising inside the baby’s skull and is considered a medical emergency. This means the soft spot remains visibly raised, firm, or tight even when the baby is sitting up, calm, and not crying. The increased pressure is often caused by swelling or a buildup of excess fluid within the brain cavity.
Conditions such as hydrocephalus (accumulation of cerebrospinal fluid) or brain swelling following a head injury can result in a bulging fontanelle. Serious infections like meningitis or encephalitis can also cause this tense bulging. These conditions require immediate medical intervention to prevent potential damage to the developing brain tissue.
A bulging fontanelle is particularly alarming when it is accompanied by other symptoms. Seek emergency medical attention if the tense soft spot is present along with a fever, excessive sleepiness, or difficulty arousing the baby. Other warning signs include a high-pitched cry, persistent vomiting, or new-onset seizures.
When to Worry: Signs of Dehydration (Sunken)
A noticeably sunken fontanelle is a key indicator of severe dehydration. While a slightly concave soft spot is normal, a deeply depressed appearance suggests that the fluid volume supporting the brain has dropped too low. This condition can develop quickly if a baby is ill and experiencing excessive fluid loss from diarrhea, vomiting, or fever.
The most common cause is an insufficient intake of fluids to compensate for this loss. If the fontanelle appears deeply depressed, caregivers should immediately look for other physical signs of dehydration. These include fewer than six wet diapers in a 24-hour period and a lack of tears when the baby is crying.
Other symptoms pointing toward dangerous fluid loss are a dry mouth, tacky lips, or a lethargic disposition. If the sunken fontanelle is present alongside extreme unresponsiveness or if the baby refuses fluids, emergency care is necessary. For a mildly sunken spot with no other severe symptoms, contact a pediatrician immediately for guidance.
Handling, Protection, and Closure Timeline
Despite how vulnerable the soft spots may appear, they are covered by a thick, durable membrane that offers substantial protection to the underlying brain. Parents do not need to avoid touching the area during routine care. Light handling, washing the baby’s hair, and wearing hats are all safe, and there is no need to be overly protective during normal daily activities.
The two main fontanelles close at different times as the skull bones begin to fuse in a process called ossification. The posterior fontanelle, the smaller spot at the back of the head, typically closes first, often within the first two to three months after birth. The larger anterior fontanelle remains open longer to accommodate brain growth, usually closing between 9 and 18 months of age.
Pediatricians monitor the fontanelles at checkups to ensure they are closing within the expected timeline. If a fontanelle closes much too early, a condition known as craniosynostosis, it can restrict brain growth and may require medical intervention. Conversely, a significantly delayed closure beyond 18 months can signal underlying medical issues, prompting a doctor to investigate further.