My beef with vape cartridges is that they all inevitably get shitty towards the end. Even cartridges with metal mouthpieces and ceramic wicks still end up with burnt residue from degraded terpenes toward the end of the cart. Shitty brands of carts can start getting fucked up before you are even halfway through them. If you dab with a quartz bucket and a timer (or learn what the proper temp feels like) so that you dab in the proper low temp range you will get the most flavor and smoothest vapor for a large hit possible and then you wipe out the residues instead of letting them hang around and burn off any remainders when you heat it up again the next time you use it. Most harsh dabbing or dabbing related bad stuff comes from people hitting the vapor while it is way too hot and burning their throats (aside from maybe smoking shitty homemade product).
Residues of burnt cannabinoids and terpenes can have such things as CBN (cannabinol, bad high), methacrolein (carcinogen), and various carbonyls and aldehydes (acetylaldehyde, formaldehyde, etc.) can be produced depending on if an unscrupulous producer added a thinning agent (vegetable glycerin, propylene glycol, ethylene glycol, etc.) to adjust the viscosity of the product (usually with cheap carts and fiber wicks).
Also dry hits, hits off a partially saturated wick, or old wicks partially saturated with combustion by products can release further bad actors. Studies have been done on some of the wick materials other than porous ceramic and they have shown very bad by-products. So burnt or over-heated residues are often not your friend and also wick materials and possibly other materials such as potential contamination from the heating coil can be harmful depending on what is in it and what comes in contact with it.
To top all of this off there were studies released earlier this year before people started dying of lung disease that a bunch of synthetic terpenes or probably terps from china or wherever had tested positive for bacterial toxins and mycotoxins, they weren't exactly sure how they got there. This could easily be one of the things that is responsible for or contributing to the health problems that are cropping up now.
Dated april 2019:
I used to work in that facet of the industry for several years and I have done many kinds of extraction, distillation and the some other lab tasks that surround it such as winterization, degumming, depigmenting, and solvent reclaiming and recycling. We used to cryogenically distill our solvent gases to clean them and also run our process at cryogenic temperatures to keep things fresh and clean. I also have known people that have been involved in making oil since it got off the ground around 2004-2005, some of the first people to start companies when it was medical before it became legal. People I know have been dabbing oil probably daily or almost daily for about 15 years now and they are healthy. These are people who wne t through the entire process of learning and figuring out what to do and what not to do and they smoked a lot of dirty product early on before people figured it out. I don't think there was anything you could consider actual clean oil until maybe 2009 at the earliest. People didn't even know to distill the heavy hydrocarbons out of their solvent gas before then, let alone how to use vacuum ovens and vacuum pumps to take residual solvents down to sub PPB levels. Those people are all fine right now, healthy active people. Maybe they get cancer down the road but they are perfectly healthy now. All of the new health problems cropping up zre 100% vape-pen and cartidge related, or possible related to dirty synthetic terps.
Also as somebody with a very high tolerance who smokes high end flower (usually 25-30% thc or slightly higher) and various forms of dabbale concentrates on a daily basis and has for a long time vape pens especially with oil or distillate doesn't really do much for me. I find vape pens to be a bit harsh on the throat as there is no water or other form of cooling of the vapor. They tend to make my throat get raspy which then makes it suck to smoke or dab other stuff too. I really avoid them unless I am traveling and I have no other choice and then when I do I avoid anything that was distilled unless I personally know who made it (afriend of mine runs a lab that specializes in that and he is very good at it) or usually I also avoid supercritical or subcritical CO2 extacts because I think it is a terrible technology for cannabis extraction, which is another long technical discussion that is too long for here but I have many good reasons (10 or so) why I think CO2 is a bad solvent for cannabis extraction.
This is already way too long