Thirdhand smoke is not the smoke we see and inhale while someone is smoking, nor the one that lingers briefly in the air after a cigarette is extinguished. It is a permanent residue of nicotine and hundreds of other chemicals that cling to walls, floors, furniture, fabrics, toys, window glass, plastic, electronics, car interiors – and even to the skin and hair of humans and pets. Once attached, these substances slowly transform, chemically changing in contact with other compounds in indoor spaces (e.g., with nitrous acid in the air), re-evaporate into the air (re-emission), or rise with dust. Because of this, the problem does not end when the smoke disappears from sight: smoke residues become part of the space and can remain there for months or years.

Why the topic is extremely current right now

In December 2025, California officially highlighted thirdhand smoke as an environmental risk in real estate transactions by passing Assembly Bill 455 (AB 455). This law, driven by years of research by university teams and public health experts, is the first in the world to oblige sellers and landlords to disclose to potential buyers and tenants whether the space has been exposed to tobacco smoke and thirdhand smoke residues. Implementation begins on January 1, 2026, and the practice will include standardized statements and clear obligations for real estate agents. Regardless of whether we live in the USA or Europe, the message is universal: the problem is recognized at the legislative level because it is based on measurable chemical and health facts.

What “thirdhand smoke” means scientifically

Unlike secondhand smoke – a mixture of smoke from a burning cigarette and the smoker's exhalation that briefly fills a space – thirdhand smoke is what remains afterwards. It includes nicotine, polycyclic aromatic hydrocarbons, aldehydes (e.g., formaldehyde), tobacco-specific nitrosamines (TSNAs), phenols, and other decomposition and oxidation products. In indoor spaces, these compounds bind to porous surfaces (fabrics, carpets, upholstered furniture, cardboard, books) and smooth materials (glass, laminate, wall paint), where they can subsequently react – for example, nicotine in contact with HONO (nitrous acid) creates nitrosamines, a group of known carcinogens. Because of such reactions, the risk depends not only on the number of cigarettes smoked but also on the characteristics of the space, ventilation, humidity, and the time elapsed since the last smoking.

Practical experience and measurements show that deposits persist extremely stubbornly on carpets, curtains, upholstery, and wall paints. In many apartments and vehicles, nicotine is detected long after smoking has stopped, despite airing out and regular cleaning. In extreme cases, the smell and chemical traces remain even after deep cleaning or repainting, pointing to the need for thorough remediation or replacement of porous materials.

Who is most exposed and why

The most vulnerable group is infants and small children. They crawl, touch floors, toys, and textiles, and then put their hands and objects into their mouths; additionally, they breathe closer to the floor, where dust accumulates. Their skin and mucous membranes are thinner and more permeable, and their respiratory and immune systems are developing. Pregnant women, people with asthma and COPD, the elderly, and pets (who lick fur where chemical residues are caught) are also exposed to increased risk. Special attention should be paid to interiors where chronic patients, children with repeated respiratory infections, and sensitive skin conditions reside.

What research says: biomarkers, inflammation, damage

In recent years, controlled studies have been conducted examining how staying in a room “contaminated” with thirdhand smoke affects the human organism. Subjects showed increases in biomarkers of exposure to nicotine and nitrosamines, indicators of oxidative stress and inflammatory response. Experimental animal models showed changes in lipid metabolism, slowed wound healing, inflammatory changes in the lungs, and neurobehavioral effects at exposure levels comparable to real-world conditions. Field measurements in apartments, hotel rooms, rental vehicles, student dormitories, and nursing homes regularly confirm the presence of nicotine and TSNAs in dust and on surfaces, even where smoking is formally prohibited. This is possible due to the transfer of residues via the clothes, skin, and objects of smokers and the “moving in” of contaminated items or furniture into non-smoking households.

How to recognize that a space has a problem

• A persistent, “stale” smell of smoke that returns after cleaning and airing indicates permanent deposits.


• Yellowish or brown stains on walls and curtains, a sticky film on glass and smooth surfaces, and color changes around ventilation vents are typical signs.


• Laboratory detection of nicotine and TSNAs in dust and surface swabs gives the most reliable confirmation; in some countries, rapid indicative tests for surfaces are also available.


• In vehicles, deposits linger in seat textiles, ceiling linings, and air conditioning ducts; during warm days and cabin heating, the smell and emissions intensify.

What to do: practical measures to reduce exposure

The most important measure is zero tolerance for smoking indoors – no “exceptions at the window” or short airing. Ventilation can reduce concentrations in the air but does not remove deposits from surfaces. If you enter a space you suspect has been exposed to smoking, plan for systematic removal of deposits in the following order:

1. Thorough mechanical cleaning and multiple vacuuming with a HEPA filter vacuum; wipe surfaces with damp cloths (not aerosols that raise dust).


2. Washing washable surfaces with mild detergents with pH adapted to the material; avoid aggressive acids and ozonizers that can create additional irritating compounds.


3. Deep cleaning of textiles with steam; if the smell and “stickiness” remain, plan for the replacement of carpets, curtains, and upholstered furniture, especially in children's rooms.


4. Removal or washing of soft items with the highest load (pillows, plush toys, bedspreads) – using high-temperature programs when permitted for the material.


5. Degreasing and then painting walls. The “encapsulation” approach has proven effective: a primer that blocks stains (e.g., shellac-based) then a top coat with low VOC.


6. Service and cleaning of the ventilation system and replacement of all filters; if necessary, cleaning of ducts.


7. For vehicles: replacement of the cabin filter, detailed chemical cleaning, treatment of ventilation ducts and, if necessary, replacement of linings that permanently emit odor.

Important: not even the most meticulous remediation guarantees complete removal in spaces with a long history of smoking. In such cases, the only more permanent answer is often a combination of replacing porous materials and hermetically sealing remaining surfaces along with long-term ventilation.

What the California model (AB 455) brings and why it is globally significant

AB 455 treats thirdhand smoke similarly to mold or radon: as an environmental factor of which the consumer must be informed before signing a purchase or lease agreement. This sets expectations in the market: buyers and tenants can request proof of professional cleaning, replacement of critical surfaces, and, if possible, swab findings from key points (children's room, kitchen, ventilation vents). For agents and owners, this means introducing risk assessment and remediation documentation procedures. Although it is a Californian law, experience shows that transparency standards quickly spill over to other markets through contractual practices and user expectations, especially in short-term rentals and student accommodation.

Secondhand smoke and thirdhand smoke: different paths, connected risks

Secondhand smoke is a mixture of mainstream and sidestream smoke, with columns of evidence regarding risks: heart attack and stroke, lung cancer, asthma exacerbation, infections in children, adverse pregnancy outcomes. The proportion of sidestream smoke can be dominant in a room and contain more toxic ingredients due to incomplete combustion. Thirdhand smoke is, on the other hand, an “after-effect” – its exposure is usually lower in immediate concentration but is longer-lasting and often unnoticed, with dermal, oral, and inhalation intake from surfaces and dust. In households with children, both risks accumulate because children spend more time on the floor and indoors.

Guidelines for parents, tenants, and employers

• Introduce and enforce a policy of total non-smoking indoors (apartment, office, vehicle). Smoking on the balcony or window is not enough – air currents often return aerosols to the interior.


• When renting or buying, explicitly ask about smoking history and request documentation on remediation and measurements. Include a smoking ban clause in the contract.


• Kindergartens, schools, clinics, and homes: before moving in or renovating, perform indicative swabs and a remediation plan; choose materials and coatings that facilitate cleaning and reduce absorption.


• In homes with babies, watch out for soft floorings and carpets; wash plush toys and textiles regularly, and replace them if necessary.


• Do not rely on “magical” devices like ozonizers – they can produce irritants and negatively affect air quality.


• Employers: include a smoking ban in official vehicles and all indoor spaces, including sanitary and storage zones, in work regulations.

What we know, and what we are still researching

What we know: (1) The chemical signature of tobacco (nicotine, TSNAs) is routinely detected in dust and on surfaces in spaces where smoking occurred – and in those where contaminated objects are brought in. (2) People in such spaces develop measurable biomarkers of exposure. (3) Usual ventilation, scents, and air fresheners do not solve the problem but can mask it. (4) Children are disproportionately affected due to behavior and physiology. What we are still researching: dose-response in real home conditions, long-term clinical outcomes in the population, and cost-effectiveness of specific remediation procedures. Although the scientific body is rapidly growing, the precautionary principle for children and pregnant women remains a reasonable rule.

Questions and Answers

“If no one smokes in my apartment anymore, am I safe?”
Not necessarily. Deposits can last for months or years, especially in porous materials. Pay attention to smells and sticky surfaces and conduct at least a thorough cleaning and replacement of soft elements.

“Can thirdhand smoke travel with people?”
Yes. Clothes, hair, and personal items of smokers transfer molecules that then settle in other spaces. That is why nicotine is often found even in households that prohibit smoking.

“Is an e-cigarette the solution?”
E-cigarette aerosol has a different chemical profile than combustion smoke but still leaves residues (including nicotine) on surfaces. A policy of total non-smoking indoors remains the best practice.

“Is there a safe level of exposure?”
For secondhand smoke, public health institutions clearly state that no safe level exists. For thirdhand smoke, although measurements are more complex, it is reasonable to target the minimum possible exposure – especially for children and pregnant women.

How to assess and document remediation

For property owners and managers and large employers, it makes sense to establish a standard operating procedure:

• Initial assessment (visual inspection, questionnaire on smoking history, indicative swabs).


• Remediation plan with cost estimate (replacement of materials, works, measurement plan).


• Execution in phases with control swabs after each key stage (e.g., after carpet removal, after painting).


• Final report with photos, invoices, and laboratory findings, which is attached to lease or sale contracts if necessary.

What you can concretely do today, December 9, 2025

If you are deciding on a lease or purchase today, explicitly request written information about the smoking history and space remediation and, if feasible, swab results from critical points (children's room, kitchen, ventilation vents). If you are an employer planning a move to new offices in 2026, include thirdhand smoke in the due diligence list and technical specifications for adaptation (removal of porous materials, encapsulation coatings, swabs before handover). In everyday life, establish a rule: no smoking in the house and car – always.

Context for public policies

Laws banning smoking in indoor public spaces have significantly lowered exposure to secondhand smoke in hospitality, offices, and public transport. Thirdhand smoke, however, opens a new question of private spaces: homes, apartments, student and tourist accommodations, and vehicles. The model of mandatory risk disclosure (as in AB 455) is one answer; others are complete “smoke-free buildings,” contractual clauses, incentives for remediation, and education of owners and users. As the evidence base expands, such policies will, expectedly, increasingly become a standard outside the USA as well.

The most important conclusion for readers is that thirdhand smoke is not a myth nor pure smell, but a measurable combination of chemicals that lingers in our living and working spaces and can contribute to health problems – especially in children. Prevention starts with a clear rule of non-smoking indoors and reasonable caution when choosing and furnishing a space.