In short yes they are compared to traditional cigarette smoke with 1000+ chemicals and ingredients however with E-cigs they only contain a hand full of ingredients.
Main ingredient PG(propylene glycol) this is also used in tradtional cigarettes but in a much higher dose surprisingly it is also added to food colorings and flavorings because of its sweet flavor. The potential for long-term oral toxicity of pg is low. In one study, rats were provided with feed containing as much as 5% PG over a period of 104 weeks they showed no apparent ill effects.
VG(vegetable glycol) used to make the vapor production and to give a satisfying throat hit . This usually makes up about 20-30% of the E-juice this is pretty much the as safe as pg it used as a substitute for people who are allergic to pg. There are some E-juices that are 100% VG.
Flavorings people use a lot of differnt flavorings most just use loran oils or alcohol based products.
Sweetener they use Ethyl Maltol(most popular), plain sugar, or sucrose.