What Causes Blackhead Type Things In My Breasts?

I've recently discovered that I have blackhead type things in my breasts. I only noticed them yesterday, so I started to tweeze them out. When they come out, they are strings coated in something white and have tiny blonde hairs on either side of them. I was wondering what exactly these things are and if they are a danger to my health? If they are, how do I get rid of them?