Small raised bumps on my arm with two holes on either side

Over the past 6 months I have been getting bumps on my arms (3 so far) with two small holes on either side. If left for long enough you can squeeze it and white solid stuff with a black tip will come out of both the holes. It looks really horrible although you can only see it if you look really close at it. Does anyone know what it might be? Serious? Or nothing to worry about?

Thanks