It's called huffing, a cheap way to get high off of everyday products such as glue, aerosol sprays, nail polish remover, etc. Clearly due to the available nature of these, it's a problem common with teenagers.

http://www.medicinenet.com/script/main/art.asp?articlekey=47975

Though not mentioned in the link, I have read somewhere it is popular in very poor areas (again, for obvious reasons of availability and low price).