WHAT IT IS: Dermal melanocytosis, also known as slate-grey naevi, blue-grey spots or Mongolian blue spots, occur due to the entrapment of melanocytes in the dermis of the developing embryo.
HOW IT IS IDENTIFIED: Dermal melanocytosis appear as patches that are darker than the surrounding skin. They are found in new-born babies. The spots tend to disappear by the time a child has reached the age of 4. They may look similar in appearance to bruises however dermal melanocytosis tends to be more homogenous and uniform in colour. History and thorough inspection are necessary to avoid misdiagnosing as non-accidental bruising (and vice versa).
Source: A Handbook Mind The Map, Clinical signs in Black and Brown Skin. Mukwende M, Tamony P, Turner M