After reading loads of abstracts on vaporizing marihuana and tobacco it seems to me that no PAHs, acrolein and benzene are present in the vapor when it's produced at 175C. So a lot of the carcinogenic components are not produced because there's no pyrolysis. I guess if the leaf contained some radioactive compounds from the start then those will end up in the vapor, though. The one thing I couldn't find out is the amount of nitrosamines that can be expected to be present in tobacco vapor vs tobacco smoke. If anybody can point me to relevant research, that would be greatly appreciated. In any case, oriental tobaccos and virginias should be safer than burley and the average reconstituted tobacco, that's pretty clear.