? Idiopathic Guttate HypoMelanosis
If these were not trauma induced, they are probably guttate hypomelanosis. It is felt that these are caused by effete melanocytes; basically melanocytes that have taken too much of a punch from the sun and are essentially knocked out. I remember reading a study of this which attested that it was more common in those with brown hair and brown eyes. It is more apparent in darker skin.
This is obviously a harmless condition and really only a cosmetic concern.