At a glance
| Chemical family | Tobacco-specific nitrosamine (TSNA) |
| CAS number | 64091-91-4 |
| Classification | IARC Group 1 (carcinogenic to humans); California Proposition 65 listed |
| Where you encounter it | Tobacco smoke (mainstream and sidestream), thirdhand smoke residues on indoor surfaces, surfaces in spaces where smoking has occurred, dust in tobacco-affected environments |
| Sleep micro environment relevance | Accumulates on pillowcases, sheets, and mattresses in tobacco-affected environments; can re-form on surfaces from deposited nicotine reacting with indoor HONO; OEHHA No Significant Risk Level can be exceeded from bedding exposure alone in heavily-contaminated environments |
| Activated carbon capture | High — TSNAs adsorb well on activated carbon based on tobacco product research and air filtration literature |
Regulatory & certification status
Where NNK stands across the major regulatory systems and the certifications a bedroom product might carry. Each row links to the governing instrument; where a jurisdiction has no specific measure, that is stated plainly rather than left blank.
| European Union | No specific restriction identified. NNK (CAS 64091-91-4) is a tobacco-specific nitrosamine handled as a research/reference compound rather than a registered industrial chemical. No entry naming NNK was found on the REACH SVHC Candidate List, and no harmonised CLP classification for NNK was found in CLP Annex VI. (ECHA infocards are bot-blocked, so registration/restriction status could not be machine-queried for this CAS; absence is reported as not confirmed rather than positively verified.) Note: recent EU CLP action on nitrosamines is a generic group approach and does not name NNK individually. Regulatory — ECHA |
| United States | Federal TSCA: no EPA risk evaluation or TSCA regulatory action was identified for NNK, which is treated as a tobacco-smoke constituent / research analyte rather than an industrial TSCA chemical. California Proposition 65: NNK is listed as known to cause cancer, effective 1 April 1990; OEHHA records the listing mechanism as "Authoritative Bodies — International Agency for Research on Cancer." OEHHA's chemical record shows a No Significant Risk Level (NSRL) of 0.014 µg/day. No reproductive-toxicity listing or MADL is shown. Regulatory — OEHHA |
| Canada | No specific restriction identified. No listing of NNK was found on CEPA Schedule 1 (List of Toxic Substances) or among Chemicals Management Plan assessments; as a tobacco-specific nitrosamine it is not a general industrial-inventory substance. (The official ECCC substances-search database could not be queried successfully for this CAS at the time of review, so absence is reported as not confirmed rather than positively verified. No final assessment placing NNK on Schedule 1 was identified, and no draft assessment is claimed.) Regulatory — ECCC |
| Australia | No specific restriction identified. No listing of NNK was found on the AICIS Australian Inventory of Industrial Chemicals or in the IChEMS Online Register; it is supplied in Australia as a certified analytical reference standard rather than as an introduced industrial chemical. (Inventory searches could not be exhaustively confirmed for this CAS, so absence is reported as not confirmed rather than positively verified.) Regulatory — AICIS · DCCEEW |
| United Kingdom | No specific restriction identified. No listing of NNK was found on the GB Mandatory Classification and Labelling (GB MCL) list, the UK REACH SVHC Candidate List or the UK REACH Authorisation List; GB largely mirrors the EU position, where NNK is also not individually listed. (HSE lists could not be machine-queried exhaustively for this CAS, so absence is reported as not confirmed rather than positively verified.) Regulatory — HSE |
| International | The International Agency for Research on Cancer classifies NNK as carcinogenic to humans, Group 1, evaluated jointly with N'-nitrosonornicotine (NNN) in IARC Monographs Volume 100E (2012). The monograph's overall evaluation states: "4-(Methylnitrosamino)-1-(3-pyridyl)-1-butanone and N'-nitrosonornicotine are carcinogenic to humans (Group 1)." NNK is not listed under the Stockholm Convention on Persistent Organic Pollutants. Regulatory — IARC Monographs Vol. 100E · IARC |
| Certifications | CertiPUR-US: does not screen for NNK — its foam content/emissions program targets formaldehyde, regulated flame retardants, heavy metals and certain phthalates, not tobacco-specific nitrosamines. OEKO-TEX Standard 100: applies a general N-nitrosamines limit of 0.5 mg/kg per individual nitrosamine (and 5 mg/kg sum of nitrosatable substances), aimed at residues from rubber/elastomer textile components; its enumerated nitrosamine list (e.g. NDMA, NDEA, NDELA, NPYR) does not include NNK, so NNK is not a named/dedicated screen. GREENGUARD / GREENGUARD Gold: a low-VOC chemical-emissions certification that does not specifically test for a semivolatile compound like NNK. Industry — CertiPUR-US · OEKO-TEX |
| The 72-hour test window | Largely missed. NNK is a semivolatile organic compound (SVOC) that, in thirdhand-smoke chemistry, deposits onto surfaces and partitions into settled house dust rather than off-gassing into air, so a short ~72-hour VOC chamber test does not reliably capture it. Detecting it requires surface-wipe or settled-dust analysis (e.g., LC-MS/MS), not a headspace VOC screen. Inferred — from the compound's volatility/emission profile versus the VOC focus of short chamber tests |
What it is
NNK is one of the two dominant tobacco-specific nitrosamines, formed during tobacco curing, processing, and combustion (the foundational classification of this chemical class was established by Hecht & Hoffmann 1988). It is a yellow crystalline solid with a distinctive aromatic odor (though typically undetectable at exposure-relevant concentrations). The compound is a potent carcinogen in laboratory animals, causing lung tumors at low doses and forming DNA adducts that drive tumor formation through documented mutagenic mechanisms — reviewed in Hecht 2012 for the lung carcinogenesis pathway. The IARC Group 1 classification is based on combined human epidemiological evidence and the mechanistic data on DNA adduct formation.
The thirdhand smoke chemistry that makes NNK consequential for non-smokers in tobacco-affected environments: nicotine deposited on indoor surfaces (walls, fabrics, dust) reacts with nitrous acid (HONO) in indoor air to form NNK directly on the surface. This means NNK can be created on bedding long after smoking has stopped, as long as residual nicotine remains and ambient HONO levels are sufficient. The 2010 Sleiman et al. study in PNAS and subsequent thirdhand smoke research has quantified this surface-formation pathway in controlled chamber experiments. Peer-reviewed
How it gets to the bedroom
From active tobacco smoke
Direct exposure to mainstream or sidestream tobacco smoke deposits NNK on all room surfaces. In smoking households, NNK accumulates on bedding within days of smoking onset and persists for months after smoking stops.
From surface re-formation (thirdhand smoke)
The 2010 Sleiman et al. PNAS study established that deposited nicotine reacts with indoor HONO to form NNK on surfaces. Peer-reviewed The implication: a former smoker's bedroom continues to produce NNK on the bedding for as long as the underlying nicotine reservoir remains. Matt et al. (2014) and Quintana et al. (2017) thirdhand smoke field studies extended this finding to characterize the persistence pattern across years of post-smoking exposure. Peer-reviewed
From inherited contamination
Moving into a home where previous occupants smoked exposes new residents to the existing thirdhand smoke reservoir. The 2014 Matt et al. study found that thirdhand smoke contamination persists for at least 6 months after smoking-cessation in former smoker homes, and longer in many cases. Peer-reviewed Bedding in such environments accumulates NNK at concentrations that can exceed health-based reference values.
From house dust
NNK measured in indoor dust in tobacco-affected environments has been reported at concentrations capable of exceeding California's OEHHA No Significant Risk Level (NSRL) for cancer risk based on bedding exposure alone in heavily contaminated environments. Peer-reviewed
What the research says
Documented health effects
NNK is one of the best-characterized human carcinogens in environmental toxicology. The IARC Group 1 classification is supported by mechanistic data on DNA adduct formation (4-hydroxyaminobutyric acid metabolite forms covalent bonds with DNA bases — detailed in Hecht 2020), animal carcinogenicity at low doses, and human epidemiological evidence linking tobacco-specific nitrosamine exposure to lung, oral, esophageal, and pancreatic cancers.
The infant and child exposure pathway is particularly concerning. Infants in tobacco-affected environments encounter NNK through skin contact with contaminated surfaces, dust ingestion (hand-to-mouth contact in crawling and pre-crawling stages), and inhalation of off-gassing nicotine and surface-formed nitrosamines. The 2017 Quintana et al. characterization of nicotine on pillows documented retention on cotton pillowcases sufficient to produce sustained child exposure through skin contact during sleep. Peer-reviewed
Internal Philip Morris research archives reviewed by Whitlatch & Schick 2019 document NNK and nicotine persisting on indoor textile and surface materials (carpet, curtain, textured wallpaper) for more than 50 days after exposure ended — establishing the long-residence thirdhand smoke chemistry that makes pre-occupied living spaces an ongoing source of NNK exposure. Peer-reviewed
Open questions
The specific dose-response between NNK exposure from bedding contamination and adult cancer risk has not been precisely quantified — partly because tobacco-affected populations typically have additional exposure routes that complicate attribution. The infant and child exposure dose-response, in environments where bedding is the primary tobacco-related exposure source, is similarly under-characterized.
What helps reduce exposure
Tier 1 — Most effective. Eliminate active smoking in the bedroom and in spaces sharing air with the bedroom. For inherited contamination from previous occupants, replacement of soft furnishings — mattresses, pillows, bedding, carpets, curtains — is the most reliable remediation. Surface cleaning helps but cannot reach the foam-core reservoirs in mattresses and upholstered furniture.
Tier 2 — Worth considering. Wash all bedding at high temperatures multiple times to reduce surface nicotine and NNK before reuse. Repaint walls (with sealing primer first) to reduce wall-surface reservoirs. Replace carpet if budget allows; the carpet pad in particular is a persistent reservoir.
Tier 3 — Larger interventions. Professional thirdhand smoke remediation services exist for severe contamination, but cost varies widely and effectiveness depends on willingness to replace soft furnishings. For pregnant women and parents of infants, the question of whether to occupy a previously-smoked-in space is genuinely difficult; the public health literature generally recommends remediation to baseline before infant occupancy in heavily-contaminated environments.
The Embr capture system addresses NNK by capturing both off-gassing nicotine (which prevents further on-surface formation of NNK) and the NNK itself. The bidirectional architecture catches NNK traveling from contaminated bedding into the breathing zone and from any new sources entering the room.
What does NOT help
Air fresheners and ozone generators do not remove NNK from soft furnishings. Ozone can react with nicotine to form additional irritant byproducts. Air fresheners mask odor without addressing the chemical reservoir.
Surface cleaning alone leaves the foam-core reservoir intact. Wiping down hard surfaces helps. The mattress, upholstered furniture, and carpet underlay remain reservoirs unless replaced.
"Smoke smell gone" does not mean "NNK gone." Olfactory adaptation and decline in the most volatile odor compounds happens within months. The semivolatile and surface-bound NNK persists much longer than the perceptible smoke odor.
Open research questions
- The exact persistence timeline of NNK on bedding fabrics in real-world (not chamber) conditions has been characterized over months but not consistently over years. Speculation
- The infant-specific cumulative dose from thirdhand-smoke-contaminated bedding has not been measured in any published cohort study with NNK biomarker endpoints.
Citations
- International Agency for Research on Cancer. NNK (Group 1 — Carcinogenic to humans). IARC Monographs. Regulatory
- California Office of Environmental Health Hazard Assessment. Proposition 65 listing and No Significant Risk Level for NNK. Regulatory
- Sleiman M et al. (2010). Formation of carcinogens indoors by surface-mediated reactions of nicotine with nitrous acid, leading to potential thirdhand smoke hazards. PNAS. Peer-reviewed
- Matt GE et al. (2014). Thirdhand tobacco smoke: Emerging evidence and arguments for a multidisciplinary research agenda. Environmental Health Perspectives. Peer-reviewed
- Quintana PJE et al. (2017). Nicotine concentration on pillow as biomarker of thirdhand smoke exposure. Nicotine & Tobacco Research. Peer-reviewed
- Whitlatch A, Schick S (2019). Thirdhand Smoke at Philip Morris. Nicotine & Tobacco Research, 21(12). DOI 10.1093/ntr/nty153 Peer-reviewed — internal Philip Morris archive documents nicotine and NNK persisting on indoor surfaces (carpet, curtain, textured wallpaper) for >50 days after exposure ended
- Hang B et al. (2018). Thirdhand smoke causes DNA damage in human cells. Mutagenesis. Peer-reviewed
- Hecht SS, Hoffmann D (1988). Tobacco-specific nitrosamines, an important group of carcinogens in tobacco and tobacco smoke. Carcinogenesis, 9(6):875-884. DOI 10.1093/carcin/9.6.875 Peer-reviewed — foundational TSNA review
- Hecht SS (2012). Lung carcinogenesis by tobacco smoke. International Journal of Cancer, 131(12):2724-2732. DOI 10.1002/ijc.27816 Peer-reviewed
- Hecht SS (2020). Metabolism and DNA Adduct Formation of Carcinogenic Tobacco-Specific Nitrosamines in Smokeless Tobacco Products. In: Smokeless Tobacco Products. DOI 10.1016/b978-0-12-818158-4.00007-8 Peer-reviewed
Frequently asked questions
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Can I detect NNK in my home myself?
Not practically. NNK measurement requires specialized analytical chemistry — typically GC-MS or LC-MS/MS in a research laboratory. Some commercial environmental testing companies offer thirdhand smoke screening, but these are typically aimed at landlord-tenant or real estate disputes rather than personal home assessment. The absence of measurement does not mean absence of contamination in spaces where smoking has occurred.
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How long does NNK persist on bedding after smoking stops?
Months to years, depending on cleaning practices and ventilation. The Sleiman 2010 PNAS finding that NNK can re-form on surfaces from deposited nicotine reacting with HONO means that even thorough cleaning does not stop the formation pathway as long as the nicotine reservoir remains. Replacement of soft furnishings is the most reliable remediation.
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Is thirdhand smoke really a cancer risk?
The mechanistic evidence (DNA adduct formation, mutagenic activity in human cells per Hang et al. 2018) supports yes, particularly for infants and children with developing systems and higher per-body-weight exposure. The epidemiological evidence at the population level is harder to disentangle from active and secondhand smoke exposure histories.
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Can washing remove NNK from pillows?
Surface washing reduces accumulated NNK on the pillowcase. The pillow foam core retains nicotine that continues to react to form NNK over time. For pillows used in tobacco-affected environments, replacement is more reliable than washing.
Related compounds
This page describes documented chemistry and exposure pathways. It does not provide medical advice. Anyone concerned about thirdhand smoke exposure in their environment should consult appropriate professional remediation guidance.
Last reviewed May 16, 2026.