Naevus flammeus, commonly known as a port-wine stain, is a permanent birthmark that appears as a pink, red, or purple patch on the skin, most often visible from the moment of birth. This distinctive marking affects approximately 3 out of every 1,000 babies and can appear anywhere on the body, though it shows up most frequently on the face and neck. Unlike other birthmarks that fade over time, port-wine stains persist throughout life and may change in appearance as a person ages.
How Common Are Port-Wine Stains
Port-wine stains represent one of the most typical forms of vascular birthmarks seen in newborns. Research shows that this condition affects roughly 0.3% to 0.5% of all babies born worldwide[1][2]. This translates to about 3 in every 1,000 infants who enter the world with this distinctive marking on their skin.
One reassuring aspect of port-wine stains is their equal opportunity nature. The condition does not favor one gender over another, affecting boys and girls at the same rate[2][4]. Similarly, port-wine stains appear across all racial and ethnic backgrounds without preference, making them a truly universal phenomenon that transcends demographic boundaries. Whether a family has light or dark skin, the chances of a baby being born with a port-wine stain remain consistent.
What Causes Port-Wine Stains
The underlying cause of port-wine stains lies in the way certain blood vessels develop beneath the skin. Specifically, these birthmarks result from abnormally formed capillaries, which are the tiniest blood vessels in the human body[2]. In areas affected by port-wine stains, these capillaries become dilated, meaning they stretch wider and remain more open than they should be under normal circumstances.
When capillaries dilate this way, they allow more blood to collect within them than usual. This increased blood flow and collection creates the characteristic reddish or purplish appearance that gives port-wine stains their name. The color comes directly from the hemoglobin in the blood that fills these enlarged vessels just beneath the skin’s surface.
Scientists have made significant progress in understanding the genetic mechanisms behind port-wine stains. Research has identified a somatic activating mutation in the GNAQ gene, located on chromosome 9[1][3]. This genetic change appears in isolated port-wine stains as well as in cases associated with Sturge-Weber syndrome. The mutation essentially provides faulty instructions to cells during development, leading to the formation of these abnormal blood vessels.
Other genetic mutations have been linked to port-wine stains when they occur alongside other conditions. Mutations in genes called RASA1 and EPHB4 have been found in cases where capillary malformations appear together with arteriovenous malformations[1][4]. Additional genetic variations involving PIK3CA, AKT1, and GNA11 genes have been connected to various syndromes that include port-wine stains as one component.
Evidence also suggests that the nervous system plays a role in the development and progression of port-wine stains. Studies examining the tissue of these birthmarks reveal a decreased presence of nerve fibers surrounding the blood vessels[7]. These nerve fibers normally help keep blood vessels narrow by maintaining their tone. Without adequate nerve supply, the vessels may lack the signals needed to constrict properly, contributing to their permanent dilation.
Risk Factors for Developing Port-Wine Stains
Unlike many medical conditions, port-wine stains do not have traditional risk factors that increase or decrease a person’s likelihood of developing them. The vast majority of cases appear spontaneously without any identifiable predisposing factors or family history[1][4]. This sporadic nature means that most families affected by port-wine stains have no previous history of the condition and no obvious reason why their child developed the birthmark.
However, familial cases do occasionally occur, suggesting that in some situations, there may be an inherited component[1]. When port-wine stains run in families, they may be part of a genetic syndrome rather than isolated occurrences. In these instances, the birthmark appears alongside other physical features or health conditions that together define a recognizable syndrome with a known genetic basis.
The timing of port-wine stain development is typically at or very shortly after birth, classifying them as congenital conditions. Rarely, acquired port-wine stains can develop later in adolescence or adulthood, usually following some form of physical trauma to the skin[1][4]. This unusual variant, sometimes called Fegeler syndrome, appears and behaves identically to congenital port-wine stains but has a different trigger related to injury rather than developmental processes during pregnancy.
Symptoms and Physical Appearance
Port-wine stains present as clearly defined patches of discolored skin that stand out from the surrounding normal skin. At birth, these birthmarks typically appear as flat, smooth areas colored pink, red, or purplish-red[2][5]. The boundaries of a port-wine stain are usually well-demarcated, meaning there’s a clear line where the birthmark starts and stops, rather than a gradual fade into normal skin tone.
The location of port-wine stains varies considerably from person to person. The face and neck represent the most common sites, with studies indicating that between 70% and 90% of cases involve the head and neck region[4][11]. When appearing on the face, they often affect one side, though they can be bilateral or centrally positioned. The scalp, arms, legs, and trunk can also be affected, and in some cases, port-wine stains appear on mucous membranes inside the mouth or other body cavities.
Size and shape vary tremendously. Some port-wine stains measure only a few millimeters across, while others span several centimeters or more, occasionally covering large portions of a limb or significant areas of the face. They can appear as a single patch or, less commonly, as multiple separate areas. The birthmark may affect one side of the body or be positioned along the midline, though they typically don’t cross the body’s centerline.
Port-wine stains are generally painless and cause no physical symptoms beyond their appearance[4][5]. They don’t itch, burn, or produce any uncomfortable sensations. The affected skin doesn’t bleed spontaneously, though it may bleed more easily than normal skin when injured or scratched, and this bleeding can sometimes be difficult to control[2].
As children grow, port-wine stains grow proportionally with them, maintaining roughly the same relative size compared to the child’s overall body dimensions[2][5]. However, the appearance often changes significantly over time. The color typically darkens with age, shifting from lighter pink shades toward deeper red, purple, or even brownish tones. The texture also evolves in many cases, transforming from smooth and flat in childhood to thicker and bumpy in adolescence and adulthood. Some people describe this textural change as feeling like pebbles beneath the skin[2][5].
In some instances, the tissue underlying a port-wine stain may also be affected. The soft tissues, including fat, muscle, and even bone, can grow larger than normal in the area beneath the birthmark[4][11]. This overgrowth, called hypertrophy, occurs most commonly when port-wine stains affect the face and can lead to asymmetry or distortion of normal facial contours over time.
Prevention of Port-Wine Stains
Currently, there is no known way to prevent port-wine stains from developing. Because these birthmarks result from blood vessel abnormalities that occur during fetal development, they form before birth and are typically present when a baby is delivered[5][10]. The genetic mutations and developmental processes that lead to port-wine stains happen spontaneously during pregnancy and are not influenced by maternal behavior, diet, activities, or environmental exposures.
Parents should understand that there are no lifestyle modifications, supplements, medications, or other interventions during pregnancy that can reduce the risk of a baby being born with a port-wine stain. These birthmarks are not caused by anything the mother ate, any stress she experienced, any medications she took, or any activities she performed during pregnancy. This understanding is important for preventing unwarranted guilt or self-blame among parents of affected children.
While the birthmarks themselves cannot be prevented, complications associated with port-wine stains can sometimes be minimized through early intervention. Starting treatment early in life, particularly during infancy, offers the best chance of reducing the birthmark’s appearance and preventing some of the texture and color changes that occur with age[6][13]. Early treatment may also help prevent the development of raised, bumpy areas and reduce the risk of bleeding complications.
For port-wine stains located on sun-exposed areas, protection from ultraviolet radiation is advisable. Sun exposure can cause these birthmarks to darken more than they would naturally, making them more noticeable. Using sunscreen regularly on the affected skin, particularly products containing zinc oxide or titanium dioxide, can help prevent this additional darkening and protect the sensitive skin of the birthmark from sun damage.
How Port-Wine Stains Affect the Body
At the most basic level, port-wine stains represent a structural problem with blood vessels in the skin. The pathology centers on the capillaries and postcapillary venules in the upper layers of the skin, specifically in the dermis, which is the layer of skin beneath the thin outer epidermis[7]. These tiny vessels are present in everyone’s skin, but in port-wine stains, they are abnormally dilated and may be present in greater numbers than normal.
Examination of port-wine stain tissue under a microscope reveals these dilated blood vessels lined with normal-appearing endothelial cells, which are the cells that form the inner lining of blood vessels. Despite their abnormal size, the vessels don’t show signs of active growth or proliferation[7]. This distinguishes port-wine stains from true tumors like hemangiomas, which involve actively dividing and multiplying cells. Instead, port-wine stains are true malformations, meaning the vessels formed incorrectly during development but aren’t growing abnormally afterward.
The depth of the abnormal vessels in port-wine stains averages about 0.46 millimeters beneath the skin surface, placing most of them in relatively superficial layers[7]. This shallow location is one reason why laser treatments can effectively target these vessels, as the light energy doesn’t need to penetrate deeply to reach them.
The nervous system’s involvement in port-wine stains extends beyond their initial formation. Studies have demonstrated that the density of nerve fibers surrounding blood vessels in port-wine stains is significantly lower than in normal skin[7]. This reduced innervation likely contributes to the vessels’ inability to maintain normal tone and constriction. Without adequate nerve supply, the vessels remain dilated, and this dilation tends to worsen over time, explaining why port-wine stains darken and become more prominent with age.
Research also points to the role of vascular endothelial growth factors (VEGF) in port-wine stain development. These proteins normally regulate blood vessel formation and maintenance, but they may be overproduced in port-wine stains[4]. Excessive VEGF activity could contribute to the progressive dilation of vessels and potentially explain why these birthmarks tend to become more prominent over time.
When port-wine stains occur as part of a syndrome, the underlying pathology extends beyond the visible skin changes. In Sturge-Weber syndrome, for example, similar vascular malformations affect the brain and the tissues covering it, leading to neurological complications[5][10]. In Klippel-Trenaunay syndrome, the blood vessel abnormalities affect deeper structures and can involve bones and soft tissues, causing the affected limb to grow larger than normal[2].