Third-hand smoke is what lingers in the environment long after Second-hand Smoke (SHS) has cleared from a space. Third-hand smoke settles onto hard, non-porous (walls, floors, ceilings, windows, furniture, some objet d’art) and soft surfaces (clothing, hair, skin, upholstery, curtains, vehicle interiors, pets), where it off-gases the same hazardous materials as in SHS. Air filters are ineffective in filtering the ultrafine particles (0.1 – 0.3 micrometers) of Third-hand smoke.
Even if a person smokes near an open window or door, significant amounts of SHS can re-enter the space. Each time a person smokes in an enclosed space (vehicles, homes, cigar bars, other indoor spaces—even those with good exhaust ventilation), tobacco smoke settles onto every surface, building up layers of toxic residue. This residue is difficult to remove completely, and most likely settled onto inaccessible surfaces as well. Particulate matter can be re-suspended with normal use of the space. Indoor spaces and surfaces contaminated with third-hand smoke can smell unpleasant.
At this time, there is scant research on the health effects of third-hand smoke in adults. Many studies, however, show the harms of second-hand smoke on infants and children.
Infants and young children are especially vulnerable to third‐hand smoke exposure because they are more likely to touch, play with, and place their mouths on objects and surfaces, including people, furniture, and toys, that are contaminated with third‐hand smoke particles. They crawl on floors and furniture and inhale (breathe in) particles that cling to carpet fibers and floor dust. Children are known to ingest (eat or breath in) twice the amount of dust that adults do, mainly due to having a faster respiration (breathing) rate and being in closer proximity to surfaces like floors. Children also have brains and organ systems that are still developing and are more susceptible to low levels of toxins. Like children, pets are also susceptible for some of the same reasons.
Similar to low‐level lead exposure, low levels of tobacco particulates may be associated with cognitive deficits among children. Studies indicate that higher exposure levels (as evident in high levels of cotinine in the blood or saliva) are correlated with lower reading scores among children. These findings underscore the possibility that even extremely low levels of these compounds may be neurotoxic and, according to researchers, justify restricting all smoking in indoor areas inhabited by children.
It is important to be aware of this invisible hazard. Third-hand smoke provides even more reason to quit smoking. Smoking outdoors, smoking in someone’s absence, and airing out a room or car will not completely eliminate the risk of exposing other people to toxins in third‐hand smoke that linger after you put out your cigarette. If you don’t smoke, avoid places where other people may smoke whether they smoke in your presence or not.