A baby’s soft spot, or fontanelle, is a normal anatomical feature present at birth. While it may seem delicate, its appearance can vary, and a slightly sunken look is often part of healthy development. Understanding these variations can ease parental concerns.
Understanding the Soft Spot
A baby’s skull consists of several bony plates connected by fibrous sutures, not a single solid bone at birth. Where these sutures meet, wider gaps known as fontanelles feel softer to the touch. The most prominent is the diamond-shaped anterior fontanelle on the top front of the head. A smaller, triangular posterior fontanelle is at the back.
These soft spots serve two purposes. They allow the skull bones to overlap and compress during passage through the narrow birth canal, facilitating delivery. They also accommodate the rapid growth of a baby’s brain, which nearly doubles in size during the first year.
The anterior fontanelle, measuring 0.6 to 3.6 cm, typically closes between 12 and 18 months, though it can remain open up to 24 months. The smaller posterior fontanelle (0.5 to 0.7 cm at birth) often closes within two to three months. A normal soft spot should feel relatively flat or slightly concave and might gently pulsate, reflecting the baby’s heartbeat.
Everyday Reasons for a Sunken Appearance
A sunken soft spot can worry parents, but it often stems from common, non-alarming factors. Mild dehydration is a frequent reason, occurring even with slight fluid loss. This can happen with slightly fewer feeds, time in a warm environment, or after longer sleep. The soft spot may temporarily dip inward, returning to normal once the baby is fed and rehydrated.
Body position also influences the soft spot’s appearance. When lying down, the fontanelle might look slightly more sunken than when upright. Vigorous crying or straining can also temporarily alter skull pressure, making the soft spot appear more concave. For some babies, a slightly sunken soft spot is simply a normal anatomical variation, even when well-hydrated and healthy.
When a Sunken Soft Spot Indicates a Problem
While often benign, a sunken soft spot can signal a more serious issue when accompanied by other symptoms. Primary concern is moderate to severe dehydration, requiring prompt medical attention. Beyond a markedly sunken fontanelle, signs of significant fluid loss include decreased urination (fewer wet diapers), dry mouth and lips. The baby may also appear lethargic, unusually sleepy, have sunken eyes, or lack tears when crying.
Other indicators of severe dehydration include lack of skin elasticity (skin remains tented when pinched) and reduced activity. A persistent or very pronounced sunken soft spot can also signal illness. If it appears alongside symptoms like high fever, persistent vomiting, severe diarrhea, or refusal to feed, these combined signs warrant immediate medical evaluation. These combined symptoms, not the sunken soft spot alone, are key to identifying a serious problem.
Knowing When to Seek Medical Help
Knowing when to seek medical help for a sunken soft spot is important. Immediate medical attention is necessary if the soft spot is markedly sunken and accompanied by severe symptoms. These include extreme lethargy or unresponsiveness, high fever, persistent vomiting, or severe, watery diarrhea. A significantly sunken fontanelle combined with severe dehydration signs or a sudden change in alertness and behavior requires an urgent emergency room visit or immediate emergency services contact.
Contact a pediatrician if the sunken soft spot persists for hours or days, even without severe symptoms. Also call if the baby is not feeding as much, appears less active, or if you feel uneasy. Trust your instincts; seeking professional medical advice is always safest. Professionals can assess the baby’s condition and rule out concerns, as self-diagnosis or treatment should be avoided.