Talk to Urologist on White Substance

Hi, I am noticing a white substance on foreskin under the head of penis, not on the head it's below the head on foreskin, it's not causing any irritation but i m worried about it,, it's been there for long, i noticed it when I was 16,, it comes out of the skin as a thick substance after sometimes and then again grows there,, I am quite worried about it, please help