Green’s Dictionary of Slang

1. (drugs) an injection into the flesh rather than directly into a vein.

1952		(con. 1948) G. Mandel Flee the Angry Strangers 61: If you like junk you keep schmeckin and shootin, then the skin pop goes to the big pipe.
1964		Larner & Tefferteller Addict in the Street (1966) 35: A few months after that I took my first shot. That was a skin-pop.
1971		R.D. Pharr S.R.O. (1998) 352: I’m only going to joy-pop [...] A skin-pop can’t hurt nobody’.
1989		(con. 1940s) Courtwright & Des Jarlais Addicts Who Survived 70: She took the spike and hit me. This was no mainline she gave me, this was a skin pop.
1992		S.L. Hills Tragic Magic 18: I had what is called a skin-pop [...] it was just a matter of injecting it into the fat part of my arm.

2. attrib. use of sense 1.

2004		J. Ellroy ‘Hot-Prowl Rape-O’ in Destination: Morgue! (2004) 274: The rabbi [...] vibed skin-pop junkie.
2009		(con. 1960s) J. Ellroy Blood’s a Rover 31: He lived off digitalis and skin-pop amphetamine.