Your point about the application of heat changing the equation for some of these substances seems especially valid. Once you've taken a breath, feel free to tear down their peg information: 3. PEG or polyethylene glycol Glycols are alcohols, not oils. The non-toxic types such as PEG have no inhalation concerns. PEG is said to present flavors better than any other base liquid. It is the least common carrier liquid. It can be made in many different formulations, the one used for e-liquid is called PEG400. This formulation appears to be chosen as it has the right viscosity, as PEG can be thinner, thicker, or even in the form of a wax or powder. As far as we know there is little research on inhalation but it cannot be toxic as it is used in foods and medicines. For example it is used as the main ingredient in a very large number of laxatives, where it is supplied in the form of a powder, with electrolytes, for mixing to a drink that has a safe laxative effect. Because it handles flavors so well it is used by several of the major cartomizer-only (2-piece ecig) firms that mainly sell to first-time buyers, as it works well in cartos. We think it comprises 1% or less of bottled eliquid sales volume but it is far higher in the pre-filled carto market - perhaps as much as 33%. PEG is the most likely of all the three base materials to be contaminated with DEG as the manufacturing process can be carried out using the same equipment, so there is a risk of cross-contamination. The part about deg was wtf for me so... DEG Diethylene glycol is one of the many glycols, and toxic to humans and animals. It is a poison that kills by damaging the liver and kidneys among other effects. It is similar to PG and PEG in appearance, taste and characteristics, and it is produced in the same way from similar raw materials and as a by-product of similar manufacturing processes, although PEG seems especially implicated. It is therefore likely to be found in any materials of this type due to poor manufacturing controls or cross-contamination - for example, using drums for PEG400 that previously contained DEG. For this reason it is the main contaminant that should be tested for.