A lot of the health problems that are arising with e-cigs is with the food flavoring. Food flavoring is not meant to be inhaled, and are causing a lot of the symptoms that most people say may be caused by PG allergies, VG allergies, and tobacco withdraw. The thing is, there are 3 known dangerous inhalant ingredients in some food flavorings: 2,3-butanedione(diacetyl); 2,3-Pentanedione (acetylpropionyl); & 2,4-pentanedione (Acetoacetone, acetylacetone, diacetylmethane, pentanedione). I will not get into too much detail, but the first one (Diacetyl) is linked to the popcorn lung disease and is also a cause of "tightening" in the chest area as well. The two ingredients after Diacetyl are Diacetyl replacements. Acetyl propionyl is also known to be just as bad as Diacetyl.
Now, even though there are liquids without those three ingredients, there could be other potential ingredients that may be causing the various symptoms of muscle cramping, tightness in the chest, swollen glands, shortness of breath, etc. We just don't know what is in the food flavorings because of the mislead ingredient message of, "artificial flavorings."
My honest opinion is to DIY, but in a different way. Buy unflavored nicotine e-juice (there are two kinds of nicotine: pesticide grade and pharmaceutical grade. Will get to that later) , food flavoring from Capellafoodflavoring.com, FlavourART, AP, etc., and either a PG, or VG base diluent. Fill the cartridge/cartomizer with unflavored nicotine, and then dip the mouth end of the cartridge/cartomizer into the food flavoring bottle. That way you can ingest the food flavoring, and receive the nicotine through the unflavored e-juice with the vaping sensation.
Now, another option to be on the safe side is to look for a brand of e-juice called, "ECOpure". I would recommend ECOpure Rich, because that is the only one I have tried (and it actually taste good). There is not much selection for flavorings, but they are the cleanest and have the fewest ingredients available in e-juice right now. The only two places that I know who sells it is, intellicig.com (Europe) intellicig-usa.com (USA), and cignot.com.
There is another company that also has random batch testing done on their e-juice, and they have records on their website is, "esmoke.net". I don't know much about their juice, but I am looking into it. They have clean juice, but I don't know how their flavoring is made.
Edit: As of right now, it is hard to tell which vendors are selling pharma grade nicotine with their premixed e-juices, and who is using pesticide grade nicotine. Basically, pesticide nicotine has a yellowish color. The color is caused from not distilling the plant material. That is another reason you may want to DIY, or buy from a "trusted" vendor. The only company that I have info on who uses pharma nicotine is TW (Totally Wicked).
Now granted, I have been a little vague in my responses on the various topics that I have mentioned, but I hope that helps you out.
Edit: I have had shortness of breath, and I have had tightening of the chest, and muscle cramping since I started vaping. However, ever since I have been using the ECOpure brand, I have not had any problems with shortness of breath, dry skin spots, tightening of the chest area, and irritated throat. The same goes for my DIY mentioned earlier in this post.
