Cig smoke has something like 69 PROVEN carcinogens and several thousand other chemicals. Unless there is somehow H2SO4 in Vapor there is no possible way that is it more harmful than analogs.
However for arguments sake lets look at the actual ingredients shall we:
1. Propylene Glycol - PG has been used as the aqueous-based chemical additive in asthma inhalers and nebulizers since the 1950s, with no serious side effects known. PG, because of its water-retaining properties, is the compound of choice for delivering atomized medication. It is also a common diluent for injectable medications, constituting 40 percent of the intravenous form of Phenytoin, an anti-seizure drug. The FDA includes Propylene glycol on its list of substances Generally Recognized as Safe (GRAS), and it meets the requirements of acceptable compounds within Title 21 of the Code of Federal Regulations. Considering PG has been widely used for many years without serious side effects, the substance can reasonably said to be of negligible concern.
2. Vegetable Glycerine - VG is one of the most benign organic liquids known to man. It is hype-allergenic, non-carcinigeic, non teratogenic and non-mutagenic. It is metabolized quite easily by a process called beta-oxidation. This process results in the production of CO2 and H2O and is a quite normal, common, and natural catabolic process. VG is of low toxicity when injested, inhaled, or in contact with skin. The most common noted side effect of inhalation of e-liquid containing vegetable glycerin is a dry mouth, sore throat, and increased thirst. These symptoms usually last just a few days to a week as the body gets used to the vegetable glycerin.
3. Flavorings - AFAIK all flavorings used are already approved by the FDA for use in food. As I have already mentioned, you are already inhaling the flavorings every time you SMELL something made with them. Since these have been used for years, if inhalation was a problem, we would already know about it.
4. Nicotine - Since this is the primary addictive agent in analogs this is WHY most people turn to vaping instead of quitting cold turkey. It is NOT known to be a carcinogen and is found in nearly every stop smoking aid including the gum, patches, and lozenges. While not necessarily safe, it is approved by the FDA for the other stop smoking aids.
The only other possible source of safety concern for eCigs would be the materials used for wicks and the coils. Some concern has been raised as to the safety of silica wicks in that particles of fiberglass like material can potentially splinter off and get stuck in the mouth, throat, and lungs. To the best of my knowledge this has neither been proven nor disproven. >>Please correct me if I am wrong.<< This can be remedied by using cotton wick material. I do not know of any real concern raised at this time about the standard Kanthal or Nichrome based coil wires.
Bottom line, I have ZERO concerns at this point about vapor being harmful beyond any risks associated with the nicotine itself. If you are still concerned then don't vape.