Suggest Remedy For Puss Filled Black Heads

Hello, My mother has what looked like a black head on the back of her neck. The ones that have the indent rather then the pop out bump. She said she had it for years. Well tonight I went to dye her hair and I noticed it. So I asked her about it and I popped it. It was like orange cream looking pus came out. It didnt ooze out like luquid but like a pimple. She said she didnt feel it nor did it hurt. It smelt kinda bad and it scared me due to how much puss came out. It took me three times to pop it to get it all out. What could it be?