Hi, my 4 year old son has had a white lump on one of his nipples since he was born. It looks a bit like a large white head. 2 doctors have said 'don't worry about it', without saying what it might be. One said we could pop it with a pin if we wanted, which we tried today - much to my poor son's discomfort - but it was hard and didn't pop. It was irritating earlier, itching, and it looked red after he scratched it. We would like to get it sorted out. What might it be and what can we do about it?