I don't know for sure whether they scar (perhaps it is different with different people) but I know that you could give yourself an infection. What I used to do is get a washcloth with as hot water as you can stand, and press it against the pimple for a few minutes to encourage all the pus to the surface. Then sterilize a pin by holding it in a flame for a few seconds, then pop the surface of the pimple and gently squeeze all the pus out that will come. It sounds a bit of trouble but it's really not; better safe than sorry...