My Dad had a large lump on his back shoulder that looked similar to a black head . But, it was larger than a usual one and more under the skin. My mom decided to pop it, and the discharge was similar to one like a pimple but was much less oily and smelled bad. The other thing is that a lot of puss came out. Do you have any idea what it could be? My Dad is in his late twenties and has no severe medical history . He has delt with mild acne before but nothing like this.