While it's considered safe, they use Propylene Glycol (same stuff used in fog machines) and/or Vegetable Glycerin (Vegetable oil) and artificial (made in a lab) and/or natural flavoring. For me I ALWAYS opted the natural route of Vegetable Glycerin base and all natural flavoring. Propylene Glycol is a skin irritant. I too had a CE4 tank on a Ego-T 900mAh battery. I eventually stepped up to a Innokin iTaste SVD variable voltage/wattage mod and a Cobra clone rebuildable tank.