TABLE 1

Four generations of e-cigarettes

	1st generation	2nd generation	3rd generation	4th generation	Remarks
Open/closed system	Closed	Open	Open	Open	An open system is manufactured with a clearomiser which is manually filled with e-liquid A closed system is prefilled with e-liquid which is directly attached to the battery
Design	Cig-a-like	Pens/laser pointer	Tank-style devices, also called “mods”	Tank-style with better regulatory features: “regulated mods”	The design of e-cigarettes has become more complex over time Currently available devices are larger and come with temperature controls
Cartridge refill	No Refill	Refillable	Refillable	Refillable
Voltage	∼3.7–4.2 V	∼3.7–6 V	∼6–8 V	∼3–8 V with variable wattage (1–75 W)	High voltage results in heating, which causes release of toxic compounds that have health implications
Battery type and capacity	Brushed steel battery	eGO-style battery; lithium-ion battery	ICR lithium-ion or IMR lithium-ion battery	Lithium-polymer battery (Li-Po)	Most of these battery packs can short-circuit and may cause explosions
Brands	VAPESTICK, Vype Disposable, Aer Disposable and NJOY	Blu+, Eonsmoke, VaporFi Rocket, Apollo vTube 4.0 and VaporFi Pro II	VaporFi, Halo, Mig Vapor and KangerTech	V2, JUUL Vapor, South Beach Smoke, Diamond Series, Vapor Shark

ICR: LiCoO₂ cathode; IMR: LiMn₂O₄ cathode.