There are currently two types of electronic cigarettes: open systems or closed systems. The open-system allows the customer to fill it and refill it as he wishes; but this summer, open-system cigarettes have been the subject of controversy. Several people died in the United States following pneumonia due to misuse of their product: most had mixed bad additives together such as Vitamin E acetate. This is why big cigarette companies are selling closed systems: in the form of pre-filled pods. Thus, consumers are no longer likely to mix their product and put themselves in danger. They will already be prepared, controlled and certified by experienced manufacturers.