If I remember correctly, from watching "intervention", the scabs are burns from the meth pipe. Correct me if I'm wrong.
"A child does not learn to squat from the top down -- in other words, he does not suddenly make a conscious decision one day to squat. Actually, he is squatting one day and makes the conscious decision to stand." - Gray Cook
I always thought the scabs were from certain chemicles escaping through the skin while sweating...I also new a good kid who got caught up and for him after like 10 days of being wired he would imagine things crawling on him and constantly try to scratch them off leading to cuts on his arms ...either way no thanks for me I like sleep now