Birthmarks are marks that are visible on the skin. They can be either:
- pigmented birthmarks (usually brown), caused by clusters of pigment cells, or
- vascular birthmarks (usually red, pink or purple), caused by abnormal blood vessels under the skin
These pages are about pigmented birthmarks. Go to Health A-Z: vascular birthmarks for information on haemangiomas (including strawberry marks), port wine stains and salmon patches.
Pigmented birthmarks are tan or brown skin marks. They include:
- café-au-lait spots
- congenital melanocytic naevi (CMN)
- Mongolian spots
Most pigmented birthmarks are harmless and do not need treatment.
Café-au-lait spots are coffee-coloured skin patches (see main picture).
Many children have one or two of these, but if more than six have developed by the time the child is five, they may have a genetic disorder called neurofibromatosis.
Congenital melanocytic naevi
Congenital melanocytic naevi (CMN) 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.
In rare cases, they fade and may disappear altogether.
CMN range in size from less than 1.5cm in diameter to more than 20cm in diameter (giant CMN). The risk of CMN developing into skin cancer is low, but this risk increases with the size of the CMN.
As CMN can affect a person's appearance, surgery may be considered. However, this will leave scarring and may not be possible if the affected area is very large.
Surgery involves removing the affected birthmark and stitching together the edges of the skin. If the area is large, a skin graft may be required. A skin graft involves taking skin from another place, such as behind your ear, and using it to cover the wound.
If your CMN increases in size or changes shape or colour, your doctor may suggest a biopsy (where a tissue sample is taken for closer examination). See the box, top left, for when to get help.
For general information on moles, go to Health A-Z Moles.
Mongolian spots are blue-grey or bruised-looking birthmarks commonly seen in darker-skinned people. They are present at birth.
The marks usually appear over the lower back or buttocks, but can also appear elsewhere on the body or limbs.
Mongolian spots are usually a few centimetres in diameter, although they can be larger.
They may persist for months or years, but usually disappear by the age of four. They are completely harmless and do not need treatment.
When to get help
See your doctor if you notice any of the following changes in your congenital melanocytic naevi (CMN):
- colour change
- inflammation (swelling)
- open sore
- size change
- texture change