At a glance
| Chemical family | Tobacco-specific nitrosamine (TSNA) |
| CAS number | 16543-55-8 |
| IUPAC name | N'-Nitrosonornicotine; 1-nitroso-2-(pyridin-3-yl)pyrrolidine |
| IARC classification | Group 1 — Carcinogenic to humans. Evaluated in IARC Monograph Volume 89 (2007), "Smokeless Tobacco and Some Tobacco-specific N-Nitrosamines," alongside NNK. Listed by California's Proposition 65 as a known carcinogen. |
| Primary disease associations | Esophageal squamous cell carcinoma; oral and pharyngeal cancer. Strong dose-response established in prospective cohort studies using urinary NNN as the exposure biomarker (Yuan et al. 2011) |
| Where you encounter it | Tobacco smoke (mainstream and sidestream); smokeless tobacco; third-hand smoke residues on indoor surfaces in spaces where any form of tobacco has been used; saliva (formed endogenously from swallowed nornicotine) |
| Sleep micro environment relevance | Co-occurs with NNK on bedding, walls, and dust in tobacco-affected environments; forms on indoor surfaces from deposited nornicotine via the same surface-mediated chemistry that generates NNK; persists for months on indoor materials in line with the broader TSNA persistence pattern documented by Whitlatch & Schick 2018 |
| Activated carbon capture | High for the semi-volatile fraction; limited reach into the soft-furnishing reservoir, where replacement is the more reliable remediation |
Regulatory & certification status
Where NNN 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 | N'-nitrosonornicotine (NNN, CAS 16543-55-8) has no harmonised CLP classification of its own in Annex VI to Regulation (EC) No 1272/2008. It does not appear on the REACH SVHC Candidate List, the Authorisation List (Annex XIV), or as a named Annex XVII restriction, and it is not listed under the EU POPs Regulation. As a tobacco constituent it falls under the Tobacco Products Directive rather than the general chemicals framework. No EU instrument naming NNN was identified. Regulatory — ECHA · EUR-Lex |
| United States | NNN is not regulated under TSCA; as a tobacco constituent it sits under FDA's Family Smoking Prevention and Tobacco Control Act authority, where it is on FDA's Established List of Harmful and Potentially Harmful Constituents (HPHCs), associated with the carcinogen health-effect category. In 2017 FDA issued a proposed product standard that would cap the mean level of NNN in finished smokeless tobacco at 1 microgram or less per gram of tobacco (dry weight); that proposed rule (Jan. 23, 2017) was never finalised. Under California Proposition 65 it has been listed as a carcinogen since 01/01/1988 (cancer endpoint, via the State's Qualified Experts mechanism), and the U.S. NTP Report on Carcinogens lists tobacco-specific nitrosamines including NNN as 'known to be a human carcinogen.' Regulatory — OEHHA · FDA |
| Canada | No CEPA Schedule 1 listing or Chemicals Management Plan assessment for NNN was identified; it is instead managed as a tobacco-product matter. NNN is a named reportable constituent under the Tobacco Reporting Regulations (SOR/2000-273) — it appears in the regulation's schedules for tobacco constituents and for mainstream and sidestream smoke emissions, with prescribed Health Canada official test methods. No restriction under the general chemicals framework was identified. Regulatory — Justice Laws Canada · Government of Canada |
| Australia | No AICIS evaluation, IChEMS listing, or legacy NICNAS/IMAP assessment specific to N'-nitrosonornicotine was identified, and as a tobacco-specific nitrosamine it is not an agvet chemical under the APVMA. No specific restriction identified. Regulatory — AICIS |
| United Kingdom | The UK largely inherits the pre-Brexit EU position; NNN has no harmonised classification under GB CLP, and no UK REACH restriction, authorisation, or candidate-list status naming the compound was identified via HSE. No specific instrument naming the compound was found. No specific restriction identified. Regulatory — HSE |
| International | The International Agency for Research on Cancer (IARC) classifies N'-nitrosonornicotine in Group 1, carcinogenic to humans, evaluated together with NNK among the tobacco-specific nitrosamines; the IARC Monograph Vol. 100E concludes that '4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone and N'-nitrosonornicotine are carcinogenic to humans (Group 1).' These agents were also reviewed in IARC Monograph Vol. 89 (Smokeless Tobacco and Some Tobacco-specific N-Nitrosamines). It is not a Stockholm Convention POP and is outside the scope of the Minamata Convention. Regulatory — IARC Monograph Vol. 100E · IARC |
| Certifications | CertiPUR-US: does not address this compound — its programme certifies flexible polyurethane foam against a defined list of foam-relevant substances and emissions (ozone depleters, certain flame retardants, regulated heavy metals, formaldehyde, phthalates, low total VOCs, and GHS CMR-classified chemicals), not tobacco-specific nitrosamines. OEKO-TEX Standard 100: regulates N-nitrosamines as a class (a requirement added in 2020) targeting volatile/extractable nitrosamines arising from rubber and elastomer components, rather than the tobacco-derived NNN, which would not normally be present in textiles; it does not name NNN. GREENGUARD/GREENGUARD Gold: a low-VOC emissions certification that does not screen for a semi-volatile tobacco constituent like this. Industry — OEKO-TEX · CertiPUR-US |
| The 72-hour test window | Largely missed. NNN is a semi-volatile, relatively high-molecular-weight nitrosamine (MW ~177) with very low vapour pressure, so it behaves as an SVOC that partitions to surfaces and dust rather than off-gassing, and a short ~72-hour VOC emissions chamber test does not reliably capture it. Inferred — from the compound's volatility/emission profile versus the VOC focus of short chamber tests |
What it is
NNN — N'-nitrosonornicotine — is a tobacco-specific nitrosamine formed during tobacco curing, processing, and combustion. Its precursor is nornicotine, a minor alkaloid present in tobacco at 1–5% of total alkaloid mass and also produced in the human body as a metabolite of nicotine. Nornicotine reacts with nitrosating agents (nitrite, nitrous acid, and other reactive nitrogen species) to yield NNN. The chemistry was characterized in the foundational Hecht and Hoffmann 1988 review in Carcinogenesis that established the tobacco-specific nitrosamine framework. Peer-reviewed
NNN's carcinogenicity in humans is supported by both mechanistic data (DNA adduct formation in esophageal and oral tissue) and prospective epidemiology. The Hecht 2003 review in Nature Reviews Cancer, "Tobacco carcinogens, their biomarkers and tobacco-induced cancer," remains the standard reference for the TSNA carcinogenesis pathway. The IARC Group 1 classification was finalized in Monograph Volume 89 (2007), "Smokeless Tobacco and Some Tobacco-specific N-Nitrosamines," based on sufficient evidence in animals and the combined human evidence from smokeless tobacco user cohorts and TSNA-mediated DNA adduct mechanism. Peer-reviewed Regulatory
The tissue-specific cancer pattern is what distinguishes NNN from NNK at the epidemiological level. NNK is most strongly associated with lung carcinogenesis; NNN is the TSNA most strongly associated with esophageal squamous cell carcinoma and oral/pharyngeal cancer. Yuan et al. 2011 in Carcinogenesis measured urinary NNN and its glucuronide in a prospective cohort of Shanghai smokers and demonstrated a strong dose-response association with subsequent esophageal cancer — independent of urinary cotinine, total nicotine equivalents, and other tobacco biomarkers. The mechanism: NNN-derived DNA adducts form in tissue that contacts swallowed tobacco-derived material and tobacco-contaminated saliva, driving esophageal carcinogenesis. Peer-reviewed
How it gets to the bedroom
From tobacco smoke deposition
NNN appears in both mainstream and sidestream cigarette smoke and deposits on indoor surfaces alongside NNK, nicotine, and the broader tobacco-smoke chemistry profile. The relative abundance varies by tobacco cultivar, processing, and combustion conditions; NNN and NNK are typically present at the same order of magnitude in deposited residue.
From surface-mediated formation
The third-hand smoke surface chemistry that generates NNK from deposited nicotine also generates NNN from deposited nornicotine. Sleiman et al. 2010 established the surface-mediated nitrosation framework in PNAS: indoor surfaces with deposited tobacco alkaloids react with ambient nitrous acid (HONO) to form TSNAs, with reactions proceeding on timescales of hours to weeks. Knezevich et al. 2013 directly demonstrated NNN formation from nornicotine in human saliva, using deuterium-labeled compounds and LC-MS/MS — the same nitrosation chemistry that operates on indoor surfaces. Together, these studies establish that the room continues to produce NNN on the surfaces long after tobacco use has stopped. Peer-reviewed
From inherited contamination
Moving into a home where previous occupants smoked exposes new residents to both the deposited NNN and the ongoing surface formation from the residual nornicotine reservoir. Schick et al. 2013, in Tobacco Control, characterized TSNA deposition on cotton cloth in chamber experiments and documented co-deposition of NNN alongside NNK with similar surface affinity. The cotton concentration finding — that fibers accumulate the most carcinogenic fraction of the smoke at ratios elevated above the aerosol phase — applies to NNN as well as NNK. The bedding in a former smoker's bedroom is functioning as a long-residence reservoir for both compounds. Peer-reviewed
From long-residence persistence
Whitlatch and Schick 2018, in Nicotine & Tobacco Research, reanalyzed previously unpublished Philip Morris archive data tracking surface tobacco-residue chemistry over more than 100 days. The data documented nicotine and TSNAs (the NNK and NNN class together) persisting on indoor textile, carpet, and wallpaper substrates well beyond 50 days after exposure ended. The 110-day NNK measurements that exceeded incoming smoke mass apply, by the same chemistry, to NNN. The long-residence picture is not specific to NNK; it characterizes the TSNA class. Peer-reviewed
What the research says
Documented carcinogenicity
The IARC Monograph 89 (2007) Group 1 classification rests on sufficient evidence in experimental animals (tumor induction in rats and mice at multiple target sites including esophagus, nasal cavity, oral cavity), combined human evidence from smokeless tobacco user cohorts (where NNN exposure is high and disentangled from combustion smoke), and mechanistic data on NNN-derived DNA adduct formation. The Hecht 2003 Nature Reviews Cancer review remains the comprehensive synthesis of the TSNA carcinogenesis literature, including the metabolic activation pathway that generates the reactive intermediates responsible for DNA damage. Peer-reviewed Regulatory
The Yuan 2011 prospective cohort finding that urinary NNN tracks subsequent esophageal cancer risk independently of cotinine and other tobacco biomarkers is the most epidemiologically clean demonstration that NNN, specifically — not tobacco exposure in general — drives the esophageal disease signal. The implication for third-hand smoke exposure is that the NNN fraction of the deposited residue is doing distinct downstream work compared to the NNK fraction, and reducing TSNA exposure as a class is the relevant action.
Documented genotoxicity
Hang et al. 2013 in Mutagenesis demonstrated that third-hand smoke extracts — which contain the deposited TSNA mixture including NNN — cause DNA damage in human cells at doses consistent with realistic environmental exposures. The single- and double-strand breaks documented are mechanistically consistent with the TSNA-driven adduct formation that drives downstream carcinogenesis. Peer-reviewed
Tang et al. 2022 in Environmental Science & Technology quantified five separate exposure pathways — inhalation, dust ingestion, dermal uptake, epidermal chemistry, and oral mucosal contact — and found each independently exceeded California's No Significant Risk Level for tobacco-specific nitrosamines including the NNK and NNN class. The exposure routes are not theoretical or singular; they are documented at concentrations that individually exceed thresholds set by a regulatory science agency. Peer-reviewed
What helps reduce exposure
Tier 1 — most effective. Eliminate active smoking, vaping, and smokeless tobacco use in the bedroom and in rooms sharing air with the bedroom. For inherited contamination, replace high-affinity soft furnishings — mattresses, pillows, upholstered furniture, carpet, and the carpet underlay — in homes with significant prior smoke contamination. The NNN reservoir co-occurs with NNK and reduces along the same pathway; remediation does not need to be NNN-specific.
Tier 2 — worth considering. Launder bedding through multiple cycles in hot water. Repaint walls with a sealing primer to reduce wall-surface TSNA reservoirs. Replace curtains and any other washable textiles that may have absorbed the deposited tobacco residue. For air-quality during the cleanup window, HEPA + activated carbon filtration helps with the semi-volatile fraction in real time. See the flagship article The Smoke That Stays for the comparison between surface cleaning and air cleaning.
Tier 3 — larger interventions. Professional third-hand smoke remediation services target TSNAs as a class. Cost and effectiveness vary widely; the willingness to replace soft furnishings is the dominant determinant of outcome. For pregnant women, parents of infants, immunocompromised individuals, and those with documented tobacco-related cancer history, the public health literature generally recommends remediation to a measured baseline before occupancy in heavily contaminated environments.
What does NOT help
Air fresheners do not address NNN on surfaces. Fragrance masks odor without affecting the surface-bound TSNA reservoir.
Ozone generators may make the chemistry worse. Ozone reacts with deposited nicotine and other tobacco alkaloids to form additional irritant byproducts. The EPA does not recommend ozone generators for indoor air remediation, and the third-hand smoke literature has not characterized whether ozone exposure increases or decreases the NNN reservoir on contaminated surfaces.
"The smell is gone" is not "the chemistry is gone." The decline of perceptible smoke odor happens on a timescale of weeks; the surface TSNA reservoir persists for months to years. The Whitlatch and Schick 2018 Philip Morris archive data show this directly.
A single laundering cycle does not reset the fabric. Multiple cycles help reduce surface-bound TSNAs but cannot reach the foam-core reservoirs in mattresses, pillows, and upholstered furniture. For heavily contaminated soft furnishings, replacement is the more reliable action.
Open research questions
- The dose-response relationship between residential third-hand smoke NNN exposure and esophageal/oral cancer risk has not been characterized directly. The Yuan 2011 cohort data on urinary NNN was in active smokers; the residential third-hand exposure population at the equivalent biomarker level has not been studied at cohort scale. Inferred
- Whether NNN-targeted surface remediation chemistry (specific cleaning agents, sealants, or sequestrants) can durably reduce the fabric reservoir to baseline has not been characterized in controlled head-to-head studies. Spec
- The endogenous NNN formation from swallowed nornicotine in nicotine-replacement-therapy users and in cessation programs has not been fully quantified — the Knezevich 2013 finding establishes the pathway but the contribution to total NNN exposure during cessation is an active research area. Spec
Citations
- International Agency for Research on Cancer. Smokeless Tobacco and Some Tobacco-specific N-Nitrosamines. IARC Monographs on the Evaluation of Carcinogenic Risks to Humans, Volume 89. Lyon: IARC; 2007. NNN classified as Group 1. publications.iarc.who.int Regulatory
- Hecht SS. Tobacco carcinogens, their biomarkers and tobacco-induced cancer. Nature Reviews Cancer. 2003;3(10):733-744. doi:10.1038/nrc1190 Peer-reviewed
- Hecht SS, Hoffmann D. Tobacco-specific nitrosamines, an important group of carcinogens in tobacco and tobacco smoke. Carcinogenesis. 1988;9(6):875-884. doi:10.1093/carcin/9.6.875 Peer-reviewed
- Yuan J-M, Knezevich AD, Wang R, Gao Y-T, Hecht SS, Stepanov I. Urinary levels of the tobacco-specific carcinogen N'-nitrosonornicotine and its glucuronide are strongly associated with esophageal cancer risk in smokers. Carcinogenesis. 2011;32(9):1366-1371. doi:10.1093/carcin/bgr125 Peer-reviewed
- Knezevich A, Muzic J, Hatsukami DK, Hecht SS, Stepanov I. Nornicotine Nitrosation in Saliva and Its Relation to Endogenous Synthesis of N'-Nitrosonornicotine in Humans. Nicotine & Tobacco Research. 2013;15:591-595. doi:10.1093/ntr/nts172 Peer-reviewed
- Sleiman M, Gundel LA, Pankow JF, Jacob P III, Singer BC, Destaillats H. Formation of carcinogens indoors by surface-mediated reactions of nicotine with nitrous acid, leading to potential thirdhand smoke hazards. PNAS. 2010;107(15):6576-6581. doi:10.1073/pnas.0912820107 Peer-reviewed
- Schick SF et al. Thirdhand cigarette smoke in an experimental chamber: evidence of surface deposition of nicotine, nitrosamines and polycyclic aromatic hydrocarbons and de novo formation of NNK. Tobacco Control. 2014;23:152-159. doi:10.1136/tobaccocontrol-2012-050915 Peer-reviewed
- Whitlatch A, Schick SF. Thirdhand Smoke at Philip Morris. Nicotine & Tobacco Research. 2019;21(12):1680-1688. doi:10.1093/ntr/nty153 Peer-reviewed
- Hang B et al. Thirdhand smoke causes DNA damage in human cells. Mutagenesis. 2013;28(4):381-391. doi:10.1093/mutage/get013 Peer-reviewed
- Tang X et al. Thirdhand exposures to tobacco-specific nitrosamines through inhalation, dust ingestion, dermal uptake, and epidermal chemistry. Environmental Science & Technology. 2022;56:12506. doi:10.1021/acs.est.2c02559 Peer-reviewed
Frequently asked questions
What is NNN?
NNN — N'-nitrosonornicotine, CAS 16543-55-8 — is one of the two dominant tobacco-specific nitrosamines (TSNAs), alongside NNK. It is a Group 1 human carcinogen evaluated by IARC in Monograph 89 (2007), "Smokeless Tobacco and Some Tobacco-specific N-Nitrosamines," and is the TSNA most strongly linked to esophageal and oral cancer in epidemiological cohort studies.
How is NNN different from NNK?
They are sister compounds — both tobacco-specific nitrosamines formed during tobacco curing, processing, and combustion, and both evaluated as IARC Group 1 carcinogens. The principal differences are tissue specificity (NNK is most strongly associated with lung carcinogenesis; NNN with esophageal and oral cancers) and the precursor that generates each on indoor surfaces (NNK forms from nicotine; NNN forms from nornicotine, a minor tobacco alkaloid and a metabolite of nicotine). In practical third-hand smoke remediation, the two compounds co-occur and the same actions reduce both.
Can NNN form on indoor surfaces after smoking ends?
Yes. The 2010 Sleiman et al. PNAS demonstration of surface-mediated nitrosamine formation applies to TSNAs broadly, and Knezevich et al. 2013 (Nicotine & Tobacco Research) directly demonstrated NNN formation from nornicotine in human saliva — the same nitrosation chemistry that operates on indoor surfaces. The Whitlatch and Schick 2018 reanalysis of Philip Morris archive data confirmed long-residence persistence of nicotine and TSNAs on indoor materials beyond 50 days after exposure ended.
Why is NNN linked specifically to esophageal cancer?
Yuan et al. 2011 (Carcinogenesis) measured urinary NNN and its glucuronide in a prospective cohort of smokers and found a strong dose-response association with subsequent esophageal squamous cell carcinoma — independent of urinary cotinine, total nicotine equivalents, and other tobacco biomarkers. The proposed mechanism involves NNN-derived DNA adduct formation in esophageal tissue, including in tissue that contacts swallowed tobacco-derived material and tobacco-contaminated saliva.
Is NNN found outside of active tobacco use?
Yes. NNN appears in third-hand smoke residues on indoor surfaces in homes where smoking occurred — and in dust, on fabrics, and in bedding in those environments. It also forms endogenously in human saliva from swallowed nornicotine, including in users of smokeless tobacco and nicotine replacement therapy products that contain nornicotine impurities (Knezevich 2013). The third-hand smoke pathway is the relevant one for non-smoker exposure in homes formerly occupied by smokers.
Can NNN exposure from a contaminated bedroom be measured?
Yes, via urinary NNN measurement using LC-MS/MS. The Yuan 2011 prospective cohort used this approach and demonstrated that urinary NNN tracks ongoing exposure with sufficient analytical sensitivity to support epidemiological dose-response analysis. The technique is research-grade and not currently offered as a consumer environmental test, but it is the gold-standard biomarker for NNN exposure in cohort studies.
What helps reduce NNN exposure in a bedroom?
The same actions that reduce NNK exposure: eliminate active smoking and vaping in the bedroom; replace soft furnishings (mattresses, pillows, upholstered furniture, carpet) in homes with significant prior smoke contamination; launder bedding multiple cycles; consider hard-surface sealing and repainting in heavily contaminated rooms. Because NNN and NNK co-occur and share the same surface-chemistry pathway from deposited nicotine and nornicotine, remediation targets both together.
Related compounds
This page describes documented chemistry and exposure pathways. It does not provide medical advice. Anyone concerned about third-hand smoke exposure in their environment should consult appropriate professional remediation guidance and their healthcare provider for personal medical decisions.
Last reviewed May 31, 2026.