From The National Institute on Drug Abuse:
You probably know that using tobacco isn’t safe. It’s not safe to smoke it yourself, and it’s not safe to breathe in “secondhand smoke” from other people’s smoking. Now, research has found that the negative effects of tobacco smoke can stick around for a lot longer than we even knew.
Researchers are investigating the effects of “third-hand smoke”—the toxins (poisonous chemicals) from smoking that can stay behind in dust, on walls, curtains, carpets, even in your car, after someone has been smoking. One study found that the toxins from smoking collect on surfaces as dust or residue, and then are gradually released into the air, where they can be inhaled (breathed in). This process is called “off-gassing.”