What Causes White Dots On The Penis Head?

My son gets these white dots around the rim of the head of his penis. They look like tiny holes and a white puss strand will come out eventually of each. He has had these twice before but only one at a time and once the white stuff comes out they go away but the hole under his skin remains. He now has two and I'm getting concerned, I was wondering if you could please help me figure out what these are ?