What Do Greenish Blackheads On The Shaft Of Penis Suggest?

I first noticed these when I was younger, before I had any sexual activity. Id say I was 15 when I first saw these. I am 22 now. I have what looks to be greenish black heads on the shaft of my penis, the best way i can describe them are they look like double black heads, very small horizontal some verticle slivers that go under the skin at each end are little black/greenish heads, I can pop these with force but they always come back in the same spot. Some times they spread, generaly stay close together, Ive had these for years and im very concerned, its really really freaking me out, any help would be greatly appreciated.