I get that too, also if one of my darling cats or dog scratches me normally as the scab heals i get a p spot.. there is a name for it i think i think it trauma site p or something! 
Lorainne - when P appears on a traumatised or injured part of the skin, it is referred to as
Koebner's phenomenon - It was so named after the 19th century physician, Dr Koebner, who first identified the response.
AussieGuy (Confirming)