16/11/2025
The blue birth marks. Often around the lower back, sacrum or buttocks area but can also appear on the arms and legs and look like bruises.
Slate grey nevus, also known as blue-grey spots or congenital dermal melanocytosis, are a type of birthmark that are typically flat and blue-grey, or sometimes purple, in colour.
They are most common on babies with Black and Brown skin and are generally found on the sacrum and buttocks, but can also be observed on arms and legs.
Slate grey nevus are NOT bruises. They are simply the result of pigment cells, or melanocytes, not reaching the surface of the skin. They do not hurt and generally require no treatment; they often fade by the age of 4.
If you identify a slate grey nevus when doing a baby examination, or NIPE, it is important to document it. This is to avoid it later being mistaken for a bruise.
Finally - you may have heard these birthmarks called ‘Mongolian blue spots’. This is derogatory, racially insensitive terminology and should NOT be used. If you hear it used in practice, please take the time to correct it. We can all play our part in decolonising language and midwifery education.
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