Birthmarks: what’s a Mongolian Blue Spot?

In our BabyNatal Practical Baby Care classes we talk about newborn appearance, and one of the things we briefly touch on are birthmarks. These congenital irregularities of the skin can be present at birth or can appear shortly after the birth (generally within the first 2 months of life) – not all babies will have them of course, but some might, so it’s important that parents are aware. There are various types of birthmarks, and they can be caused by different factors.

This blog focuses on a particular type of birthmark called Mongolian Blue Spot, also referred to as “slate grey navi” or, formally, as “congenital dermal melanocytosis”.

What is a Mongolian Blue Spot?

The name might sound a bit intimidating (especially the formal one!), but a Mongolian Blue Spot is a harmless, pigmented birthmark. All it means is that it appears as a ‘coloured’ spot on the skin – generally, it’s blue-ish or grey-ish in colour. Other distinctive characteristics are:

  • It’s flat;
  • The affected area of skin appears of ‘normal’ texture;
  • It’s of the same colour throughout;
  • It varies in size from approximately 2 to 8cm;
  • It can be one spot of various spots;
  • It is of irregular shape.

Where can it be found?

The Mongolian Blue Spot can often be found at the base of the spine, on the lower back and buttocks. Rarely, it can also be found on arms, legs, shoulders or torso.

Who can have it?

Anyone can be born with a Mongolian Blue Spot (or develop one within a couple of months from birth), but the incidence of this birthmark is very rare in children of white European background. It is however very common in children of African, Middle Eastern, Mediterranean or Asian background, to the point that it is estimated that up to 3 fourth of children from these backgrounds are born with it.

Why do children have it?

Although there is no clear explanation as to why some children are born with this birthmark, the condition is believed to be inherited and to affect more boys than girls. Looking at the ethnicity of the babies and children affected, it is also believed that it has to do with the amount of melatonin in the skin. Potentially, it might be the product of an anomaly occurring when the baby is developing in the womb. One theory is that a certain group of cells called “dermal melanocyte” remain ‘trapped’ under the skin before the birth and end up giving the affected area its characteristic pigmentation.

What to watch out for?

As we said, the Mongolian Blue Spot is harmless – it is not painful, non-cancerous, it doesn’t appear to be linked to any other medical conditions, and it doesn’t cause any adverse health effects. For this reason it doesn’t require any special care, and it normally fades away on its own in the first years of life and almost always by puberty.

However, because of its colour and typical location, a Mongolian Blue Spot can be wrongly confused with a bruise. The easy way to tell the difference between the two is that a bruise will change colour over the course of a few days until it eventually gets better and disappears – the Mongolian Blue Spot won’t; it doesn’t change colour, and it doesn’t fade or disappear in the short space of a few days and weeks.

Mistaking a Mongolian Blue Spot for a bruise can have significant implications for a family, and this is true whether it’s the parents thinking it’s a bruise or a medical professional. It’s therefore important to know of their existence and of what to look out for.

More rarely a Mongolian Blue Spot can also be mistaken for another condition called “spina bifida occulta” (a fault of the spinal column) – once again, this is because of the usual positioning of the birthmark, but it is worth mentioning that patients affected by “spina bifida occulta” can display red birthmarks, not greyish.

If you believe that your child may have a Mongolian Blue Spot or another birthmark, it is always important to get this diagnosed by a medical professional (or more than one if necessary), to ensure that the right condition has been identified and no other underlying health concerns are present.

If you would like more information on this, the Birthmark Support Group can offer support and advice to the parents of children with any type of birthmark.

Do you have a story to tell us? Did / does your child have a Mongolian Blue Spot, and how did you find out about it?


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