Observing a baby’s soft spot can worry new parents, as its appearance may indicate health concerns. This soft area is a normal part of development, allowing for brain growth and facilitating birth. While a slightly depressed soft spot can be normal, a significantly sunken appearance signals a need for attention. Understanding typical characteristics and recognizing signs that warrant medical advice is helpful.
What Are Fontanelles?
Fontanelles are the soft spots on a baby’s head where the skull bones have not yet fully fused. These spaces are composed of tough, fibrous connective tissue, providing flexibility to the skull. This design allows the baby’s head to compress slightly during birth, aiding its passage through the birth canal, and accommodates the rapid growth of the brain and skull during the first two years of life.
There are six fontanelles present at birth, but the two most noticeable are the anterior and posterior fontanelles. The anterior fontanelle, located on top of the head, is diamond-shaped and measures about 1 to 3 centimeters at birth. The posterior fontanelle, found at the back of the head, is triangular and smaller, around 5 to 7 millimeters at birth.
A normal fontanelle should feel soft and flat, possibly with a slight inward curve. It is common to observe a gentle pulsation in this area, which is due to normal blood flow to the brain and is not a sign of concern. The posterior fontanelle usually closes by about two months of age, while the larger anterior fontanelle can close anytime between 4 and 26 months.
Reasons for a Sunken Soft Spot
The primary reason for a noticeably sunken fontanelle in infants is dehydration. This can happen due to insufficient fluid intake, or increased fluid loss from vomiting, diarrhea, or fever. When a baby is dehydrated, the body prioritizes fluid preservation, which can lead to a reduction in the cerebrospinal fluid surrounding the brain, causing the fontanelle to appear sunken.
Accompanying a sunken fontanelle, several other signs often indicate dehydration:
- Dry tongue and lips
- Dry or cool skin
- Rapid heart rate and breathing
- Infrequent urination or fewer wet diapers than usual
- Lack of tears when crying
- Sunken eyes
- Increased lethargy or fussiness
While dehydration is the most common cause, in rare instances, malnutrition can also contribute to a sunken fontanelle. Infants with malnutrition often present with other signs, such as being underweight, having dry hair that falls out easily, or exhibiting fatigue.
When to Be Concerned and Seek Help
A significantly sunken fontanelle, especially with other symptoms, warrants prompt medical evaluation. If the soft spot is noticeably caved in and your baby shows signs of severe dehydration (e.g., extreme lethargy, unresponsive behavior, very dry mouth, no tears when crying), this indicates a medical emergency. A marked decrease in wet diapers or dark, concentrated urine also points to a need for urgent professional assessment.
Additional concerning symptoms that, when combined with a sunken fontanelle, should prompt immediate contact with a pediatrician or emergency care include persistent vomiting, high fever, or difficulty breathing. A fontanelle may appear slightly sunken when a baby is calm or upright, but it should return to a flat appearance when the baby is well-hydrated and lying down. If the sunken appearance persists or worsens despite efforts to increase fluid intake, or if any of the aforementioned symptoms are present, seeking professional medical advice is appropriate.