Capillary malformation (Port wine stain/PWS)

What is a capillary malformation or port wine stain?

A red or purple mark on the skin which is present from birth. They are caused by widened blood vessels where blood flows slowly through the area all the time. A capillary malformation is sometimes called a "port-wine stain".

Capillaries are the smallest blood vessels in the body and researchers believe that these malformations occur while a child is still in the womb.

No known food, medication or activity a mother did during pregnancy can cause her child to have a capillary malformation.

How common are they?

They are the most common vascular malformation. About one in every 330 babies has a capillary malformation, with some research suggesting they are twice as common in girls.

Where do they occur?

They can occur anywhere on the body, but are more common on the face or neck. A person can also have several capillary malformations in different places on their body.

How are they diagnosed?

Usually by a doctor looking at the birthmark.


A capillary malformation can effectively be treated with laser, which reduces the widened blood vessels and can lighten the colour. Capillary malformations should be treated early for the most effective results. Untreated capillary malformations can progressively become darker in colour, and may become lumpy in appearance.

Laser treatment
Laser works best on young children, on face, neck and chest birthmarks. Capillary malformations on limbs can respond poorly to treatment. It is common to start laser treatment from the age of 6 months to one-year old. There is evidence to suggest that better results can be achieved when treating patients from a young age.

Treatment is commonly given every 6-8 weeks, until no further improvement is achieved, usually after 6-8 treatments.

Treatment result depends on the site of capillary malformation and size and depths of the abnormal blood vessels. It is clinically difficult to predict results before laser treatment is given. The majority of patients respond to treatment, but most are unlikely to have complete disappearance of the capillary malformation.

When children grow it is likely that a capillary malformation will get darker in colour. Repeated courses of laser treatment are usually needed.

Associated syndromes

Sturge-Weber syndrome
A capillary malformation appearing on the face can occasionally be related to a rare condition called Sturge-Weber syndrome (SWS). It is a neurological disorder affecting the skin, brain and eyes and can lead to epilepsy, glaucoma and learning difficulties, with symptoms often appearing in the first year of a child’s life.

If a child’s capillary malformation is on the forehead, eyelid or scalp, they should be checked by a paediatrician who may consider running an MRI scan.

Klippel-Trenaunay syndrome
Klippel-Trenaunay syndrome consists of three symptoms often seen together: capillary malformation, venous malformations and limb hypertrophy (extra growth of a limb). The syndrome is present at birth but the port wine stain is often the only visible sign. It can be difficult to diagnose until other symptoms become apparent. It affects about one in every 20,000 to 40,000 children.

Macrocephaly-capillary malformation (M-CM)
M-CM is a multiple malformation syndrome causing body and head overgrowth and abnormalities of the skin, vascular system, brain and limbs. The disorder has recently (June 2012) been attributed to a genetic mutation in a gene called PIK3CA. The mutation in M-CM is thought to always occur after cell division begins and is therefore very unlikely to be inherited. A mutation that happens at this stage results in different percentages of cells being affected in different individuals, so there is significant variability in how severely each individual is affected.

A diagnosis of M-CM is currently made based solely on clinical observations. Though not every affected individual has all features, commonly found signs include macrocephaly, congenital macrosomia, extensive cutaneous capillary malformations, body asymmetry, extra or fused fingers or toes, lax joints, doughy skin, variable developmental delays and other neurologic problems such as seizures and low muscle tone. 

This site does not provide medical advice and is not a substitute for medical or professional care, and if you see a birthmark growing or changing significantly, see a specialist.