Thank you for your question about this rare birthmark.
Naevus sebaceum is a birthmark that is often yellow and warty in appearance. It appears on the face or scalp region most commonly, and usually in childhood.
It is harmless but may increase in size over time and in some cases may even develop worrying skin cancer growths within the birthmark when the patient is older. From your photo, you do have a black pigmentation within the birthmark. This should be examined by a trained dermatologist as a biopsy of this area is likely required (ie simple procedure to take a small sample to send for testing).
In general, such birthmarks should be removed to prevent skin cancers from occurring. The best way to remove it is by surgical excision ie to cut out surgically and to close the remaining defect with stitches. This can usually be done by a Dermatologist if it is fairly small. In your case, I would recommend a visit to a plastic surgeon if you would like it completely removed. Hope this helps!
Best regards
Dr Stephanie Ho, Dermatologist
