Nevus simplex, commonly known as a stork bite, is one of the most frequently observed vascular birthmarks in newborns. This harmless mark is extremely common, seen in a significant number of infants shortly after birth. The true cause of the stork bite is not related to external trauma or mythical delivery methods, but rather a temporary change in the small blood vessels beneath the skin. This article explores the biological event that results in this benign mark.
What Exactly Is a Stork Bite?
A stork bite is the common term for nevus simplex, or sometimes a salmon patch. This birthmark appears as a flat area of pink, red, or light purple discoloration on a newborn’s skin. The patches generally have an irregular border. Up to 70% of all newborns are born with nevus simplex, making it one of the most prevalent vascular marks.
The location of the patch often dictates its nickname. When the discoloration appears on the nape of the neck, it is traditionally called a “stork bite.” Marks appearing on the face—such as on the forehead, eyelids, or between the eyes—are referred to as “angel kisses.” These common locations are situated along the midline of the body, reflecting underlying vascular development.
The Physiological Mechanism Behind the Birthmark
The development of a stork bite is fundamentally a vascular phenomenon, classified as a type of capillary malformation. It is not related to genetic factors, diet, or any action taken by the mother during pregnancy. The mark results from the dilation, or stretching, of tiny blood vessels called capillaries that sit just below the skin’s surface.
During fetal development, these small vessels become enlarged and remain dilated. Because an infant’s skin is relatively thin, the increased concentration of blood in these widened vessels creates the visible pink or reddish patch. This structural change is a normal variation in development and presents no health risk.
The color of the stork bite intensifies when the baby experiences a surge in blood flow or pressure. This is observed when an infant is crying, straining, or becoming warm from exertion. The increased pressure temporarily pushes more blood into the already dilated capillaries, making the mark appear darker red or purple. Applying gentle pressure to the mark can briefly cause the color to lighten or blanch until the pressure is released.
Prognosis and Resolution
The natural course of the stork bite is for the majority of marks to fade completely over time without medical intervention. This fading occurs as the capillaries beneath the skin mature and their walls become less dilated. Marks located on the face, such as the eyelids and forehead, generally have the best prognosis for resolution.
These facial marks, the “angel kisses,” typically disappear within the first one to two years of life. Conversely, the patches found on the nape of the neck, the true “stork bites,” are more likely to persist. Although they may lighten significantly, the neck marks can sometimes remain visible into adulthood.
Even when the neck mark persists, it is harmless and often covered by hair, making it less of a concern. Since nevus simplex is a benign condition, no treatment is necessary, and its presence does not indicate underlying health issues. In rare instances where a persistent mark is cosmetically concerning, specialized laser treatments can shrink the dilated vessels and improve the appearance.