Heated tobacco products have soared in popularity as a “smoke free” alternative to cigarettes in recent years, but a peer-reviewed report has suggested their emissions could be considered smoke — a claim strongly rejected by the tobacco industry.

Heated tobacco products, or HTPs, are often confused with e-cigarettes, which heat liquid that can contain nicotine but do not involve tobacco leaf.

HTPs instead use a high heat to decompose tobacco, via a process called pyrolysis, which does not set it on fire or burn it, therefore avoiding creating smoke.