Thirdhand smoke is the chemical residue from tobacco smoke. It is also called “tobacco smoke residue” or “stale tobacco smoke.” The chemicals in thirdhand smoke are toxic to humans, especially children. It can linger for years in dust and on household surfaces. It can also become embedded in carpets, furniture, clothes, and building materials. It is difficult and expensive to remove. People can be exposed to thirdhand smoke by touching contaminated surfaces (absorption through the skin), by eating contaminated objects or dust, and by breathing in air and re-suspended thirdhand smoke particles. There are many pollutants that can contaminate our environments. Presently, vehicle emissions and industrial air pollutants receive much-needed attention from policy makers and the public. But there remains a lot of important work to be done to protect environments from other forms of pollution, such as pollutants from tobacco smoke. A focus on tobacco smoke exposure draws attention to a source of pollution that is the result of preventable activities that can be easily changed or eliminated. For example, it is much more reasonable to ask someone not to smoke around others than to ask someone not to drive a vehicle around others. In addition, some of the toxic and cancer-causing chemicals in thirdhand smoke can only be found in tobacco smoke. This means that thirdhand smoke adds a unique mixture of harmful substances to the ones already created by pollution from cars and factories. To prevent exposure to these additional pollutants, individuals should never allow smoking indoors or near a doorway or window. Eliminating exposure to toxic pollutants is important for protecting human health. This means addressing many forms of air pollution, including tobacco smoke residue. Updated: July 2023 Sources: Jacob P 3rd, Benowitz NL, Destaillats H, Gundel L, Hang B, Martins-Green M, Matt GE, Quintana PJ, Samet JM, Schick SF, Talbot P, Aquilina NJ, Hovell MF, Mao JH, Whitehead TP. Thirdhand Smoke: New Evidence, Challenges, and Future Directions. Chem Res Toxicol. 2017 Jan 17;30(1):270-294. doi: 10.1021/acs.chemrestox.6b00343. Whitehead TP, Havel C, Metayer C, Benowitz NL, and Jacob 3rd P. Tobacco alkaloids and tobacco-specific nitrosamines in dust from homes of smokeless tobacco users, active smokers and nontobacco users. Chem Res Toxicol. 2015;28(5):1007-14. Schick SF, Farraro KF, Perrino C, Sleiman M, van de Vossenberg G, Trinh MP, Hammond SK, Jenkins BM, Balmes J. Thirdhand cigarette smoke in an experimental chamber: evidence of surface deposition of nicotine, nitrosamines and polycyclic aromatic hydrocarbons and de novo formation of NNK. Tob Control. 2014;23(2):152-9.