Split and merge into it. Answer by Runtdog. Confidence votes 7.9K. Long term drug use with heroin, crystal meth (methamphetamines), crack cocaine, etc. The drug is actually eating away from the inside out causing the sores/chancres on the skin as well as the picking of the skin and itching with the drug.plit and merge into it. Answer by Runtdog. Confidence votes 7.9K. Long term drug use with heroin, crystal meth (methamphetamines), crack cocaine, etc. The drug is actually eating away from the inside out causing the sores/chancres on the skin as well as the picking of the skin and itching with the drug.