Caused by invagination of the epidermal elements into the subcutaneous tissue as a result of trauma.
Appears as round, non-transluminating lesion, which is slow growing.
Often there is a white head at the crux of the nodule.
May become infected, usually with a staphylococci or streptococcus organism.
Usually asymptomatic.
Treatment includes surgical removal of the lesion with its lining.