The spread of electronic cigarettes (e-cigs) and of the so-called heat-not-burn (HnB), also known as heated tobacco products, presented as a less harmful alternative to traditional cigarettes, required further in-depth studies to demonstrate the real benefits or possible risks linked to this type of habit among smokers and possible new smokers. There are numerous harmful substances produced by these devices, such as metals, organic compounds, and aldehydes. The presence of formaldehyde is particularly worrying: its indoor concentration is 2.7, 1.2, and 40 µg/m3 for HnB, e-cigs, and traditional cigarettes, respectively. The evidence of this substance, which numerous epidemiological studies have already shown to be harmful to health (in particular, the International Agency for Research on Cancer classified it as a group 1 carcinogen), would lead to the need to modify the legislation with more restrictive rules on the use of these devices in public environment and in particular in the presence of more susceptible subjects, such as minors and pregnant women.