Trees

The terpenes used in vape carts to dilute and reintroduce flavor and aroma (which is lost in some extraction methods) also produces harmful byproducts when vaped. [1]

Should straight up avoid any flavored vape juices.

Some of the food-safe diluent agents used in vape products may be harmful when aerosolized and inhaled, as they were never actually studied under those conditions.

[Cannabis] extracts are not diluted in propylene glycol or glycerol like nicotine due to their hydrophobic properties. Instead, various forms of oils including vegetable oils, terpenes, and tocopheryl acetate (vitamin E acetate) have been reported as diluents. In most reported cases of EVALI, additional flavoring additives are also added to products.

Although many of these diluent agents and flavorings have been “generally recognized as safe” for oral ingestion by the FDA, recent research shows that when heated to form an aerosol and inhaled, conditions including bronchitis, bronchiolitis, acute hypoxic respiratory distress, lipoid-associated pneumonia, and pneumonitis may result. [2]

There's poor regulation when it comes to a lot of the products out there, especially those sold in gas stations and smoke shops (but also can be an issue in dispensaries).

Another problem with vape pens and e-cigs is the cheap atomizers/coils used, especially in disposables. There have been confirmed cases of these coils/atomizers leeching heavy metals into the vapor produced.[3]

This is such a new and under-studied area I personally find it's not worth risking it vaping concentrates. I'll stick with my dry herb vaping with my Volcano and Mighty+, which are actually certified medical devices. [4]