Parenthood involves learning to interpret subtle signs from your baby, and the appearance of the soft spot often causes concern. This area, known scientifically as a fontanelle, is a gap between the developing skull bones. While normal, its appearance can sometimes indicate changes in your baby’s health status. Understanding what a normal soft spot looks like and recognizing deviations is important for monitoring an infant’s well-being.
Understanding the Baby’s Fontanelle
The fontanelle is a soft, membrane-covered space that allows the bony plates of the skull to overlap slightly during birth, facilitating passage through the narrow birth canal. It also provides necessary space for the brain’s rapid growth during the first two years of life. Newborns have several fontanelles, but the two most prominent are the anterior (front) and posterior (back) soft spots.
The smaller posterior fontanelle, located at the back of the head, typically closes within the first two months of life. The larger, diamond-shaped anterior fontanelle, found on top of the head, remains open much longer, usually closing between 7 and 19 months of age. A normal fontanelle should feel firm and relatively flat, or curve slightly inward. Parents may notice a slight, rhythmic pulsing, which is simply blood flow and not a sign of danger.
Identifying a Sunken Soft Spot
A truly sunken fontanelle presents as a noticeably dipped area compared to the surrounding skull. While slight concavity can be normal, a pronounced depression that does not return to a flat or slightly concave state is a cause for concern. Parents can check by gently running a finger over the area while the baby is calm and upright.
This persistent physical sign is distinct from minor changes that occur when an infant is crying or lying down, where the fontanelle may temporarily appear slightly raised or full. A sunken fontanelle remains even when the baby is resting quietly and held vertically. This visual change indicates that something may be affecting the normal fluid balance surrounding the brain.
The Underlying Cause: Dehydration
The most frequent cause for a sunken fontanelle is dehydration. The fontanelle acts as a pressure sensor, and its sunken appearance directly reflects a drop in the volume of circulating fluids within the body. This fluid loss includes the cerebrospinal fluid that surrounds the brain, which normally provides a slight cushion and helps keep the fontanelle flat. When the body is dehydrated, it conserves fluid, leading to a reduction in this volume and causing the membrane to retract inward.
Conditions such as fever, vomiting, or diarrhea are common culprits that lead to rapid fluid loss in infants. A sunken soft spot is rarely an isolated symptom; it is typically accompanied by other observable signs that indicate fluid depletion. Parents should monitor for these physical markers:
- A significant decrease in urination, such as fewer than six wet diapers over a 24-hour period.
- Urine that is darker yellow than usual.
- A dry mouth or lips.
- An absence of tears when crying.
- Increased lethargy or unusual sleepiness.
When to Contact Your Pediatrician
If you notice that your baby’s fontanelle is persistently sunken, medical attention is warranted to assess the degree of dehydration. Immediate intervention is necessary if the sunken spot is paired with severe symptoms, such as an inability to keep fluids down, excessive vomiting, or a decreased level of alertness. These combinations of symptoms indicate a serious level of fluid loss that requires prompt medical evaluation.
If the sunken appearance is mild and your baby is otherwise acting normally, you can try offering additional fluids, such as more frequent breastfeeding sessions or extra bottles. However, if the soft spot remains sunken despite increased fluid intake, or if any other signs of dehydration are present, contact your pediatrician. Medical professionals will conduct a physical examination, including checks for skin elasticity and moisture levels, to determine the appropriate course of action, which may involve oral rehydration or intravenous (IV) fluid replacement in severe cases.