In the United States, this causes around 34,000 deaths per year.

But smoking creates yet another danger, that of “third-hand smoke”. This refers to residual tobacco substances that are in and on fabrics, furniture, floors and walls.

Indoors, this third-hand smoke can constitute a health hazard even years later.

These are the findings of a study by the Lawrence Berkeley National Laboratory. Third-hand smoke is made up of nicotine, released in the smoke, and of a molecule naturally present in the indoor air called nitrous acid.

The meeting of these two substances leads to the creation of molecules called tobacco-specific nitrosamines (TSNA), which are highly carcinogenic.

“Three different TSNAs were formed in this reaction, two of which are known carcinogens,” warns a press release based on the study.

While for a few hours they can be detected by the smell of cold tobacco, these substances settle permanently in the homes. Always present on surfaces, they evolve and come into contact with the inhabitants.

“Five different exposure pathways exceeded the ‘No Significant Risk Level’ under realistic scenarios, including inhalation, dust ingestion, direct dermal contact, gas-to-skin deposition, and epidermal nitrosation of nicotine,” the experts noted.

Continuous exposure to these substances can significantly increase the risk of cancer. If there is no way to get rid of them permanently, experts advise cleaning the furniture and walls, and changing the place of the objects.

Most of all, they recommend not smoking – failing which, to smoke outside.