Mongolian blue spots

Mongolian blue spots are a type of birthmark that is present at birth or appears soon afterwards, either single or multiple in number. It is flat, blue-grey in colour and can vary from a very dark blue to a lighter grey. The colour is usually the same over the whole birthmark, with no lighter or darker areas as is sometimes seen in brown birthmarks.

Mongolian blue spots are can vary in size, but most are a few centimetres across. They can appear anywhere on the body, but are most common at the base of the spine, the buttocks or on the lower back. Occasionally they are present on the back of the shoulder. It is very unusual for a child to have a Mongolian blue spot on the scalp or face.

What are the signs of a Mongolian blue spot and how are they diagnosed?

Mongolian blue spots are quite characteristic in appearance so do not need any special tests for diagnosis. However, because of their colour and location, they can wrongly be confused with bruising. The difference between them is that bruises change colour and shape over a period of days, whereas Mongolian blue spots take many years to fade. They are not painful to the touch and do not need any special care.

Some cases have been reported in the medical literature where children with widespread and multiple Mongolian blue spots also had metabolic disorders. This is very rare, and more research is needed to discover about this potential link. If your doctor has any suspicion that the birthmarks are linked to another condition, he or she will order various tests to make a firm diagnosis of a metabolic disorder as soon as possible. Initially, this is usually a urine test to check for specific proteins or sugars.

What causes them?

While the baby is developing in the womb, the cells that will eventually form the skin move to the surface. A particular kind of cell called a dermal melanocyte moves to the top layer of the skin between the 11th and 14th week of pregnancy. By the 20th week of pregnancy, these dermal cells usually disappear. Doctors think that Mongolian blue spots are caused when these cells have not moved to the top layer of skin and have not disappeared. As the cells are trapped deep in the skin, the affected area looks a bluish-grey colour. We do not know why this failed to happen, but it is not linked to anything the mother did or did not do during pregnancy.

How common are Mongolian blue spots?

Mongolian blue spots are rare in children of white European background, but very common in children of African, Middle Eastern, Mediterranean or Asian background. As many as three-quarters of children from these ethnic groups are born with Mongolian blue spots. As they are so common, it is likely that they are inherited but we do not yet know how. They can occur in both boys and girls, but are slightly more common in boys, although we do not yet know why.

How are Mongolian blue spots treated?

The vast majority of them do not require any treatment as they disappear on their own by the time a child enters puberty. If the birthmark has not faded by this time and is causing distress, it can be covered using cosmetic camouflage.

What is the outlook for children with a Mongolian blue spot?

As the vast majority of Mongolian blue spots disappear without treatment in a few years, the outlook is very good. In the past, there have been problems if they are diagnosed as bruising, but medical and nursing staff are now much more aware of them and less likely to make a wrong diagnosis. If you believe the diagnosis is wrong, it is alright to challenge this and ask whether it could be Mongolian blue spot rather than bruising.

Compiled by: 
The Birthmark Unit in collaboration with the Child and Family Information Group
Last review date: 
June 2013