There are several different types of birthmark and some of them are very common.

The 2 main types of birthmark are vascular birthmarks (often red, pink, purple or blue) caused by abnormal blood vessels in or under the skin and pigmented birthmarks (usually brown or tan coloured) caused by clusters of pigment cells.

Vascular birthmarks usually occur in the head and neck area, mainly on the face. However, both types of birthmark can appear anywhere, including inside the body.

Vascular birthmarks

Some of the most common types of vascular birthmarks are described below.

• Salmon patch (stork mark) — red or pink flat patches that can appear on a baby's eyelids, neck or forehead at birth. They are the most common type of vascular birthmark and occur in around half of all babies. Most will fade away within a few months but salmon patches on the forehead may take up to 4 or more years to disappear. Patches on the back of the neck often last. They are often more noticeable when a baby cries.
• Infantile haemangioma — a raised mark on the skin that is usually red and can appear anywhere on the body. These are also known as 'strawberry birthmarks'. Sometimes they are deeper in the skin, in which case the skin can look blue or purple. Haemangiomas are also common, especially in girls, and affect every 2 to 4 in 100 babies by 6 weeks of age. They increase in size rapidly for the first 6 months but will eventually shrink and usually disappear by around 4 or 5 years of age. Very bulky haemangiomas, those that rapidly increase in size and those that get in the way of vision, breathing or feeding, may need treatment.
• Port wine stain — red or purple flat marks that affect around 3 in 1000 newborn babies. They can vary in size, from a few millimetres to several centimetres in diameter. Port wine stains often occur on one side of the body and usually appear on the face, chest and back, although they can appear anywhere. Port wine stains tend to be sensitive to hormones and may become more noticeable around puberty, pregnancy and menopause. Most are permanent and may deepen in colour over time.

Pigmented birthmarks

Some of the most common types of pigmented birthmarks are described below.

• Café-au-lait spots — coffee-coloured skin patches. Many children have 1 or 2 of these, but if more than 6 have developed by the time the child is 5, see your doctor as it could be a sign of neurofibromatosis.
• Mongolian spots — blue-grey or bruised-looking birthmarks which are present at birth. They are more commonly seen in darker skinned people and usually appear over the lower back or buttocks, but can also appear elsewhere on the body or limbs. They may last for months or years, but usually disappear by the age of 4. They are completely harmless and do not need treatment. They may be mistaken for a bruise.
• Congenital melanocytic naevi (CMN) — also known as 'congenital moles'. These are relatively large brown or black moles that are present at birth. They are fairly common and are caused by an overgrowth of pigment cells in the skin. Most CMN become proportionally smaller and less obvious with time, although they may darken during puberty or become bumpy or hairy. They can range in size from less than 1.5cm to more than 20cm in diameter. The risk of CMN developing into skin cancer is low, but this risk increases with the size of the CMN.

What causes birthmarks?

It is not understood exactly why birthmarks occur, but they are not usually inherited. Vascular birthmarks are caused by abnormal blood vessels in or under the skin, while pigmented birthmarks are caused by clusters of pigment cells.

It is thought that port wine stains occur because the nerves that control the widening or narrowing of the capillaries (tiny blood vessels) do not function properly, or there are not enough of them. This means that blood is constantly supplied to the skin in that area, which makes it permanently red or purple in colour.

Port wine stains are sometimes related to other conditions, such as Sturge-Weber syndrome and Klippel-Trenaunay syndrome.

Is treatment needed for birthmarks?

Most birthmarks are harmless and do not need to be treated for medical reasons although some people seek treatment for cosmetic reasons. Some types of birthmark will fade over time whereas other types, such as port wine stains, are permanent if they are not treated. In some cases, a birthmark will need to be treated for medical reasons, for example if a haemangioma blocks the airways, affects vision or feeding or becomes ulcerated.

Laser therapy is the best available treatment available for port wine stains. It destroys the blood vessels that make up the birthmark without injuring the skin on top. Many treatment sessions are usually needed and it is not always successful.