A port wine stain is a type of birthmark made up of abnormal blood vessels in the skin. It appears at birth as a flat, pink or red patch and, unlike many other birthmarks, does not fade on its own. Port wine stains affect roughly 3 to 6 out of every 1,000 newborns, occur equally in boys and girls, and can appear anywhere on the body, though the face is the most common location.
What Causes a Port Wine Stain
Port wine stains develop because of a genetic mutation that happens randomly during early embryonic development. The mutation occurs in a gene called GNAQ, which controls signaling inside cells that line blood vessels. When this gene gets stuck in an “on” position, those cells don’t mature properly. Instead of forming normal, tightly organized capillaries, they create dilated, immature blood vessels that sit close to the skin’s surface. The red or pink color you see is simply blood showing through those widened vessels.
Because the mutation happens spontaneously in a small group of cells during fetal development (rather than being inherited from a parent), it only affects certain areas of the body. This is why port wine stains have sharp borders and typically appear on one side of the face or body. The proportion of mutated cells within the birthmark varies from person to person and correlates with severity: a higher percentage of affected cells generally means a more pronounced stain.
What It Looks Like at Birth and Over Time
At birth, a port wine stain is flat and smooth, usually pink or light red with a clearly defined edge. The size and location of the birthmark stay the same throughout life, growing proportionally as the child grows, but the color and texture change significantly with age.
During adolescence and early adulthood, the stain typically darkens from pink to deep red. By middle age, many port wine stains shift to a dark purple, which is actually where the name comes from: the color resembles port wine. The underlying blood vessels continue to widen over the decades, and in a review of more than 400 patients, about 65% had developed thickened, bumpy, or nodular skin by their 50s, with the average age of thickening around 37 years. This cobblestone-like texture can make the skin feel raised and uneven. Left untreated, port wine stains do not shrink or disappear. They only progress.
How It Differs From a Salmon Patch
Many parents confuse port wine stains with salmon patches, which are far more common and appear in roughly 44% of all newborns. Salmon patches are the flat pink marks often called “angel kisses” (on the forehead or eyelids) or “stork bites” (on the back of the neck). A few key differences help tell them apart.
- Color and behavior: Salmon patches are lighter pink and tend to deepen temporarily when a baby cries, strains, or gets warm. Port wine stains hold a more consistent, deeper red tone.
- Location pattern: Salmon patches are usually symmetrical, appearing on both eyelids or centered on the forehead. Port wine stains are typically one-sided and segmental.
- Outcome: Salmon patches on the eyelids and forehead usually disappear by age 2 to 3, and most are gone by age 6. Port wine stains are permanent and darken over time.
When a Port Wine Stain Signals Something Deeper
Most port wine stains are isolated birthmarks with no effect beyond the skin. But when they appear in certain locations on the face, they can be associated with conditions that affect the brain or eyes.
The most well-known of these is Sturge-Weber syndrome, in which the same type of blood vessel abnormality extends to the brain and the eye on the affected side. Infants with a port wine stain covering the forehead or spanning a large portion of one side of the face are considered higher risk. Current screening recommendations suggest these babies be referred early to a pediatric neurologist and monitored for seizures. Brain imaging with MRI is commonly used to check for involvement beneath the skull.
Glaucoma Risk
Port wine stains near the eye carry a risk of glaucoma, a condition involving increased pressure inside the eye that can damage vision. The risk depends on exactly where the birthmark sits. In one study of newborns with facial port wine stains, lower-eyelid involvement carried notably high odds: 83% of eyes with lower-eyelid lesions developed glaucoma, compared with 18% of those with only upper-eyelid involvement. Because of this, children with port wine stains near the eye typically receive regular eye exams starting in infancy.
Treatment With Laser Therapy
Pulsed dye laser (PDL) therapy is the standard treatment for port wine stains. The laser emits a specific wavelength of light that is absorbed by the blood inside the dilated vessels, causing them to heat up and gradually collapse. Over a series of sessions, the birthmark lightens as treated vessels close off and are reabsorbed by the body.
Treatment often requires multiple sessions, and results vary widely depending on the size, location, and depth of the stain. Many patients need anywhere from 8 to 20 or more treatments. The skin may look bruised for a week or two after each session, but the procedure is generally well tolerated.
Why Early Treatment Matters
Starting laser therapy in infancy appears to offer a significant advantage. In a study of 10 infants who began weekly treatments at a median age of 4 weeks, 7 out of 10 achieved near-total or total clearance (76% or more of the birthmark gone) after a median of just 2 months. The likely explanation is that infant skin is thinner and the blood vessels haven’t yet widened to their full extent, making them easier to target. As port wine stains darken and thicken with age, they become progressively harder to treat.
Delayed or inconsistent treatment can also allow the stain to continue progressing. Case reports show patients whose birthmarks deepened in color and developed nodules during gaps in care. This makes a strong case for beginning treatment early and maintaining a consistent schedule rather than waiting.
Emerging Treatments for Resistant Stains
Not all port wine stains respond fully to laser therapy, and some darken again after initially fading. For these resistant cases, researchers have explored combining laser treatment with a topical medication called sirolimus (rapamycin), which works by targeting the overactive cell-signaling pathways behind the abnormal blood vessels. Some studies have reported up to 50% improvement in stains that had stopped responding to laser alone. However, other trials have found no significant difference when adding the topical medication. The approach remains under investigation, and results so far are mixed.
Newer laser wavelengths, including 577-nanometer yellow lasers, are also being studied as alternatives to the traditional pulsed dye laser. These may offer advantages for certain skin types or deeper vessels, though PDL remains the first-line option for now.