Approach to a rash in the well newborn and infant: Clinical sciences

Rashes in well-appearing newborns and infants are usually benign and self-limited. These rashes can be associated with factors like hormonal shifts, immature circulation, and environmental exposures; but occasionally rashes have no apparent cause. Newborn and infant rashes can be categorized by age of onset and by rash appearance and distribution.

Now, if a well-appearing newborn or infant presents with a rash, first, you should obtain a focused history and physical exam and assess your patient’s age at the onset of the rash.

Let’s start with rashes that appear before 1 week of age. In this case, your next step is to assess the rash’s appearance.

First, let’s take a look at newborns with skin peeling. In this case, you should consider physiologic desquamation.

While most newborns experience mild skin peeling, more extensive skin peeling is seen in post-term neonates. Physical exam reveals desquamation primarily on the hands and feet, and it may extend to the limbs or trunk, especially if your patient is post-term. With these findings, you can diagnose physiologic desquamation. This benign and self-limited skin condition represents the natural shedding of the outer skin layer and requires no treatment.

Alright, let’s move on to rashes that present with transient color changes. In this case, you should assess the rash’s pattern of distribution.

First, if the color change is unilateral, you should consider a harlequin color change.

Caregivers may report a sudden onset of redness occurring exclusively on one side of the body, which resolves within 20 minutes. During the physical examination, place the infant on their side, and you may observe unilateral erythema of the dependent side, with a clear demarcation along the midline. Based on these findings, you can diagnose harlequin color change. Although the color change appears dramatic, this phenomenon is benign, self-limited, and does not require intervention.

Here’s a clinical pearl to keep in mind! Some infants are born with a reddish-pink, flat patch on the back of the head or neck that blanches with gentle pressure. This is a common vascular birthmark called a nevus simplex, or more commonly, a salmon patch or stork bite, that typically fades over the first 18 months of life.

Now, let’s move on to color changes involving the distal extremities. In this case, you should consider acrocyanosis, especially if your patient is under 2 days old.

Newborns typically present with bluish discoloration of the hands and feet. On the physical examination, you may notice that the extremities feel slightly cool to the touch, and cyanosis is present in the hands and feet, while the trunk remains well-perfused and warm. With these findings, you can diagnose acrocyanosis. This is a benign and transient phenomenon related to vasomotor immaturity, which resolves when the infant is warmed.

Let’s finish by discussing infants with widespread color changes of the skin. In this case, you should consider cutis marmorata.

These infants typically develop symmetric mottling of the skin, often after cold exposure, that resolves when the infant is warmed. During the physical examination, you will see a distinctive lacy, reticulated purple or pink coloration, often on the trunk, arms, and legs. If you see this, diagnose cutis marmorata, which is a common phenomenon that can appear at any time during the first few months of life.

Here’s another clinical pearl! Some infants are born with bluish-gray spots on the back, extremities, or buttocks that don’t change with temperature. This benign finding is called congenital dermal melanocytosis, which is a common birthmark that is often mistaken for non-accidental trauma since it appears similar to a bruise.

Now, let’s go back and take a look at infants with rashes that consist of papules or pustules. In this case, your next step is to assess the rash distribution.

If the rash is widespread, consider transient neonatal pustular melanosis or erythema toxicum neonatorum. First, let’s discuss transient neonatal pustular melanosis!

These infants typically have a rash that is present at birth, with the exam revealing vesiculopustular lesions on a non-erythematous base. Most often, the acral skin surfaces are spared. After the rash resolves, the skin is left with hyperpigmented macules, surrounded by collarettes of scale. These findings are highly suggestive of transient neonatal pustular melanosis. This rash is a benign condition that resolves spontaneously within a few weeks.

On the other hand, erythema toxicum neonatorum usually begins 2 to 3 days after birth and can persist during the first week of life. Physical exam reveals macules or papules surrounded by a blotchy erythematous base, resembling flea bites. Most often, the acral skin surfaces are spared. These findings are highly suggestive of erythema toxicum neonatorum, which is a benign condition that resolves on its own within about 10 days.