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. Thirdhand smoke penetrates deep into materials and is not easy to remove from polluted locations. Materials prone to thirdhand smoke contamination include carpets, pillows, upholstery, furniture, sheetrock, drywall, floors, and ceilings. These reservoirs make it very difficult and expensive to remove thirdhand smoke damage. Some research has been done to determine the best ways to remove thirdhand smoke. Evidence is limited but growing. Here is what we currently know about cleaning and odor removal: Common household cleaning of surfaces, floors, fabric, toys, plates, and cutlery Frequent and thorough household cleaning can reduce thirdhand smoke residue that has accumulated on surfaces and in dust. This process requires frequent vacuuming with a HEPA filter and regular wiping/washing/scrubbing of surfaces with acidic (e.g., white household vinegar) and alkaline (e.g., Simple Green) cleaning solutions. Always follow manufacturers’ instructions on the proper dilution and use of cleaning solutions. Thirdhand smoke polluted clothes, blankets, pillows, and cloth toys may be cleaned in a washing machine. Depending on how polluted the fabrics are, they may have to be washed multiple time Plates, cutlery, and plastic toys affected by thirdhand smoke may be cleaned in a dishwasher. Depending on how badly polluted the objects are, you may need to wash them multiple times. Homes have many hidden surfaces that can become polluted by thirdhand smoke such as HVAC ducts, underside of tables, insides of cabinets, backside of bookcase, wall covered by painting, mattresses, upholstery, and closets.  Cleaning these hidden thirdhand smoke reservoirs in a home can substantially reduce the presence of thirdhand smoke pollutants.  When polluted objects cannot be cleaned, they should be considered for replacement and disposal (e.g., HVAC ducts, mattresses). Caution:  Unless the underlying THS reservoirs are removed (e.g., walls, furniture, carpet backing), THS will be re-emitted from these reservoirs and continue to pollute household surfaces and dust.   Heavily Polluted Walls, Ceiling, and Floors Trisodium Phosphate (TSP) is sometimes used by professionals (e.g., painters, remediation experts) to deal with persistent thirdhand smoke residue. This method requires washing/scrubbing any and all surfaces such as doors, floors, ceilings, walls, baseboards, and floorboards before applying primers and painting. TSP is a hazardous chemical, and its safe application requires specialized tools and personal protective equipment. The long-term effectiveness of these cleaning methods is currently not well understood and depends on the severity of the thirdhand smoke damage. This type of cleaning removes accumulated residue on surfaces. However, cleaning with TSP is insufficient in removing thirdhand smoke residue that has become embedded into materials like wood panels, particle board, and drywall. After cleaning, special paint primers are sometimes used (e.g., alcohol-based) before repainting.  Priming and painting may trap thirdhand smoke residue on a wall, but painting over an exposed surface cannot remove thirdhand smoke pollutants. It might, however, temporarily remove the stale tobacco smoke odor. Reports of thirdhand smoke residue penetration through new coats of paint (i.e., “bleeding through”) suggest that painting is unlikely to be a permanent solution to thirdhand smoke. The short-term and long-term effectiveness of this approach is currently not well understood. Caution: If the walls, ceilings, and floors are heavily polluted with thirdhand smoke, it is likely that the pollutants have penetrated in the drywall and ceiling panels, into the utility ducts, and into wall insulation.  Removing pollutants from the outside of a wall does not remove the pollutants embedded in the material or behind the wall.  Removing Stale Tobacco Odor does NOT mean that THS pollutants have been removed Reducing the odor of thirdhand smoke does not protect individuals from chemical exposure. The perception of odor is how we sense chemical compounds in the air. Some hazardous chemicals are odorless or even have a pleasant smell, while other chemicals that are not harmful sometimes have unpleasant odors. Moreover, some of the thirdhand smoke pollutants are not in the air but linger on surfaces and in dust Some approaches to eliminating odors involve tricking our senses by covering up an unpleasant smell with a pleasant fragrance. However, this strategy does not remove any thirdhand smoke pollutants and may make an environment more irritating because new chemical compounds are added to the air (e.g., floral aerosols). Misperceptions about Cleaning Thirdhand Smoke Tobacco smoke quickly spreads throughout a room, to neighboring rooms, through air and utility ducts, and entire buildings.  Because thirdhand smoke is noticed in only one room, does not mean other rooms are unaffected. Covering up the unpleasant odor of stale tobacco smoke with fragrance does not remove thirdhand smoke. “Odor Killers” might succeed in you no longer being able to smell unpleasant odors. They are unable to remove THS reservoirs causing the odors. Killing and removing organic growth (e.g., mold, fungi, pests) does not affect chemical pollutants such as thirdhand smoke.  Well-maintained air purifiers with HEPA filters are effective in removing hazardous thirdhand smoke particles from the air.  However, they are not effective in removing volatile and semi-volatile chemical compounds that might be off-gassing from thirdhand smoke reservoirs.  Removing volatile chemical compounds from the air requires air purifiers with charcoal filtration. Removing thirdhand smoke pollutants from the air does not remove them from surface, inside materials or from dust. Clean, Replace, Remodel Cleaning up thirdhand smoke polluted indoor environments can be very expensive.  It all depends on how long and how much previous occupants smoked and how much thirdhand smoke has accumulated.  In some cases, washing and wiping surfaces and replacing carpets and furniture might be enough.  If tobacco has been used in an indoor space repeatedly over extended periods of time, large reservoirs of thirdhand smoke chemicals will be deeply embedded in the building materials (e.g., drywall, insulation) — in addition to lingering on surfaces. In this case, the building materials need to be completely replaced and a full renovation may be required. Updated: June 2022 Sources: Ask This Old House. Understanding Thirdhand Smoke. Home Safety Videos. Retrieved from: https://www.thisoldhouse.com/home-safety/21249597/understanding-thirdhand-smoke. Bahl V, Jacob P, 3rd, Havel C, Schick SF, Talbot P. Thirdhand cigarette smoke: factors affecting exposure and remediation. 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