At a glance
| Chemical family | Tobacco-specific nitrosamine metabolite — the reduced-alcohol biomarker of NNK |
| CAS number | 76014-81-8 |
| IARC classification | Not classified. IARC Monograph Vol. 89 (2007) evaluated and classified the parent NNK and its sister compound NNN as Group 1 (carcinogenic to humans) — but explicitly excluded NNAL itself from that overall evaluation "as a result of the limited data available." NNAL has never received its own IARC Group. |
| Role | Urinary biomarker of NNK exposure — not a compound that accumulates on bedding or off-gasses in a room |
| Where it's found | Urine of smokers, vapers, and secondhand/thirdhand-smoke-exposed nonsmokers, including children — not in house dust or on surfaces |
| Sleep micro environment relevance | Used in pediatric research to prove that thirdhand-smoke-contaminated bedding and surfaces deliver a measurable biological dose of NNK to sleeping children |
| Activated carbon capture | Not applicable — NNAL is a body-fluid metabolite, not an airborne or surface contaminant. Reducing it means reducing exposure to the parent NNK, not capturing NNAL itself. |
Regulatory & certification status
Where NNAL stands across the major regulatory systems and the certifications a bedroom product might carry. Because NNAL is a metabolite rather than an environmental contaminant, most of these rows report an honest negative: no regulatory body treats a urine biomarker as a substance to be restricted in a product. Each row links to the governing instrument where one exists.
| European Union | No specific restriction identified. NNAL (CAS 76014-81-8) does not appear on the REACH SVHC Candidate List or carry a harmonised CLP classification in Annex VI of Regulation (EC) No 1272/2008 — unsurprising, since NNAL is not manufactured, sold, or present in consumer products; it is generated inside the human body. Its parent ketone NNK is the tobacco-specific nitrosamine relevant to hazard classification, not this metabolite. Regulatory — EUR-Lex · ECHA |
| United States | No specific restriction identified for NNAL itself, and none would be expected. The California Proposition 65 list contains the parent ketone NNK — "4-(N-Nitrosomethylamino)-1-(3-pyridyl)1-butanone," CAS 64091-91-4 — listed 04/01/1990 as a carcinogen with a No Significant Risk Level of 0.014 µg/day. NNAL, the alcohol metabolite (CAS 76014-81-8), does not appear on the Prop 65 list, and OEHHA has no NNAL chemical page. NNAL is also not the subject of any TSCA risk evaluation. The two compounds are frequently and incorrectly conflated in secondary sources — this page's own history is an example of that error (see the note at the end of this section). Regulatory — OEHHA |
| Canada | No specific restriction identified. NNAL (CAS 76014-81-8) does not appear on CEPA Schedule 1 (List of Toxic Substances); the only nitrosamine on Schedule 1 is N-nitrosodimethylamine (NDMA), an unrelated, non-tobacco-specific nitrosamine. No discrete Chemicals Management Plan risk-assessment action is attributable to NNAL as a standalone substance. Regulatory — Government of Canada |
| Australia | No specific restriction identified. NNAL is not identifiable as a discrete entry on the Industrial Chemicals Environmental Management Standard (IChEMS) Register, and no AICIS evaluation action is attributable to it — consistent with its status as a metabolite rather than a manufactured or imported substance. Regulatory — DCCEEW · AICIS |
| United Kingdom | No specific restriction identified. Under UK REACH and GB CLP (administered by HSE), NNAL has no identifiable GB mandatory classification or restriction. Regulatory — HSE |
| International | IARC Monographs Volume 89 (2007) classified the parent compounds NNK and NNN as Group 1 (carcinogenic to humans). The same monograph documents NNAL's carcinogenicity in experimental animals in its exposure-data section, but states plainly that NNAL and iso-NNAL "have not been considered in the present evaluation" due to limited data at the time — meaning NNAL was never assigned its own Group classification. No subsequent IARC monograph has revisited NNAL specifically. NNAL is not a Stockholm Convention POP. Regulatory — IARC Monographs Vol. 89 |
| Certifications | CertiPUR-US, OEKO-TEX Standard 100, and GREENGUARD/GREENGUARD Gold do not name NNAL and would not be expected to — none of these programs test body fluids or biomarkers; they test manufactured products and materials. If any of these certifications is relevant to tobacco-derived nitrosamines at all, it is via the parent NNK, addressed on that entry. Industry — CertiPUR-US · OEKO-TEX |
| The 72-hour test window | Not applicable. NNAL is not an airborne or surface compound a VOC emissions chamber would ever detect — it is measured in urine by LC-MS/MS in a clinical or research laboratory, not in a materials-testing lab. Inferred — from NNAL's status as a body-fluid metabolite rather than an environmental emission |
What it is
NNAL — 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanol, CAS 76014-81-8 — is the principal metabolite of NNK (4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone), one of the two dominant tobacco-specific nitrosamines and an IARC Group 1 human carcinogen. When NNK enters the body — through active smoking, secondhand smoke inhalation, or thirdhand-smoke contact with contaminated surfaces — the liver metabolizes it via carbonyl reduction into NNAL, which is then excreted in urine, mostly as glucuronide conjugates ("total NNAL"). Analytically, NNAL is measured by liquid chromatography-tandem mass spectrometry (LC-MS/MS) sensitive to the subpicogram-per-milliliter range, a method developed by Jacob and colleagues that underlies most modern NNAL biomonitoring studies. Peer-reviewed — Jacob et al. 2008, Anal. Chem.
The classification question — answered precisely
An earlier version of this page, and the compound tile in the Atlas grid, stated that NNAL carried an IARC Group 1 classification "derived from" its Group 1 parent NNK. That was imprecise and has been corrected here. The primary IARC source — Monograph Volume 89 (2007), Smokeless Tobacco and Some Tobacco-specific N-Nitrosamines — evaluated four tobacco-specific nitrosamines and classified NNK and N′-nitrosonornicotine (NNN) as Group 1. NNAL and a related compound, iso-NNAL, are discussed in the exposure-data section of that same monograph (including a note that NNAL shows sufficient evidence of carcinogenicity in experimental animals), but the monograph explicitly states that these two compounds "have not been considered in the present evaluation" due to the limited data available at the time. IARC has not revisited NNAL specifically since. Regulatory — IARC Monographs Vol. 89
In plain terms: NNK is Group 1. NNN is Group 1. NNAL is not classified by IARC at all — not Group 1, not 2A, not 2B, not 3. Chemical similarity or a parent-child metabolic relationship is not the same thing as sharing a hazard classification, and the Atlas's own integrity standard is explicit that a classification must be confirmed against the primary record rather than inferred. On that standard, the honest at-a-glance answer for NNAL is "not classified," and this page — along with the compound tile carrying the badge — is being corrected to reflect that.
Why NNAL matters anyway: it's the proof of dose
NNAL's importance to the bedroom-chemistry story has nothing to do with an independent hazard classification and everything to do with what it demonstrates. Surface chemistry studies can show that NNK is present on contaminated bedding, walls, and dust in a former smoker's home — but a surface measurement alone does not prove a person is actually absorbing that carcinogen. Urinary NNAL closes that gap: when NNAL shows up in a nonsmoker's urine, particularly a child's, it is direct biochemical evidence that NNK from the environment reached their bloodstream and was metabolized. NNAL is to NNK roughly what carboxyhemoglobin is to carbon monoxide — a measurable downstream signature of upstream exposure, not a hazard in its own right (a role structurally similar to cotinine's relationship to nicotine).
The foundational pediatric evidence for this goes back over two decades. Hecht and colleagues first quantified NNAL and its glucuronides in the urine of elementary-school-aged children in Minneapolis, establishing that carcinogen uptake from secondhand tobacco smoke was measurable and widespread in exposed children. Peer-reviewed — Hecht et al. 2001, Cancer Epidemiol. Biomarkers Prev. A decade later, a study of 79 smoker-household parent-child dyads found detectable total NNAL in 90% of children's urine, with levels tracking home smoking restrictions almost perfectly: children in homes with complete smoking bans had roughly one-fifth the NNAL of children in homes with partial or no restrictions. Peer-reviewed — Thomas, Hecht et al. 2011, Cancer Epidemiol. Biomarkers Prev.
NNAL and the thirdhand-smoke question specifically
Here the evidence needs an honest, careful read rather than a tidy story. The 2011 study above also tested whether NNAL could specifically flag thirdhand exposure (contact with residues on surfaces, independent of any active smoking nearby) rather than ordinary secondhand smoke. The researchers measured a proposed thirdhand-specific metabolite, iso-NNAL, alongside total NNAL — and found no iso-NNAL in any of the children's urine samples, despite confirming iso-NNAL could form metabolically from its precursor in laboratory hepatocyte experiments. Their conclusion for that cohort was direct: the children's carcinogen exposure was occurring via secondhand smoke, not thirdhand smoke. Peer-reviewed — Thomas, Hecht et al. 2011
More recent pediatric research takes a different approach to isolating thirdhand exposure: rather than a distinct metabolite, the ongoing ADVOCATE cohort study (Cincinnati Children's Hospital, protocol published 2025) recruited over 1,000 children and used strict biochemical screening — salivary cotinine and hand-wipe nicotine — to sort them into a no-exposure group, a thirdhand-only group (nonsmoking households with elevated thirdhand markers but no reported secondhand exposure), and a mixed group. Within that design, the study measures urinary NNAL alongside cotinine and treats the NNAL-to-cotinine ratio as a potential marker capable of distinguishing thirdhand-dominant from secondhand-dominant exposure in children — the working hypothesis being that thirdhand exposure (dust ingestion, dermal contact with contaminated surfaces) may carry NNK independent of a proportional nicotine dose. This is described in the study as a hypothesis being tested, not an established diagnostic. Peer-reviewed — Mahabee-Gittens, Merianos et al. 2025, Pediatr. Res.
A related Cincinnati Children's analysis of 242 pediatric emergency-department patients found that higher urinary NNAL, and a higher NNAL-to-cotinine ratio, were independently associated with more urgent-care visits over six months — a finding that connects the biomarker to real clinical outcomes, even without a settled IARC classification for NNAL itself. Peer-reviewed — Merianos et al. 2022, Pediatr. Res.
The honest summary: NNAL reliably proves NNK uptake happened. Whether it — or its ratio to cotinine — can reliably distinguish which route (secondhand vs. thirdhand) delivered that dose in a given child is still being actively researched, not resolved.
What the wider biomarker research shows
NNAL's kinetics make it useful well beyond pediatrics. Its terminal half-life is considerably longer than nicotine's or cotinine's — 10.3 days in daily smokers and 17.6 days in occasional smokers — meaning it can reflect exposure over weeks rather than days. Peer-reviewed — Goniewicz et al. 2009, Cancer Epidemiol. Biomarkers Prev. A CDC NHANES analysis using 2011–2012 population data used urinary NNAL to estimate NNK dose across the US population, confirming its role as the standard national biomonitoring tool for this carcinogen in both smokers and nonsmokers. Peer-reviewed — Wei, Blount et al. 2016, J. Expo. Sci. Environ. Epidemiol. And in adult prospective cohort research, elevated urinary NNAL has itself been associated with increased lung-cancer risk, independent of self-reported smoking status and other cigarette-derived biomarkers — evidence that the exposure NNAL is tracking is not a purely academic concern. Peer-reviewed — Park et al. 2021, prospective cohort study
What helps reduce it
The action is entirely upstream, on NNK — not on NNAL. Because NNAL is generated inside the body after exposure, there is no way to "capture" or "clean up" NNAL itself; the only lever is preventing NNK exposure in the first place. See the NNK entry for the specific remediation steps: eliminating active smoking near the bedroom, replacing soft furnishings (mattresses, pillows, carpets) in homes with a history of tobacco use, and — where surface reservoirs can't be eliminated — reducing ongoing off-gassing and contact exposure.
Biomarker testing as feedback, not treatment. Periodic NNAL measurement (research-grade, via a lab using LC-MS/MS) can document whether remediation efforts are actually reducing a child's internal dose, distinct from simply reducing measurable surface concentrations. Several of the pediatric intervention studies cited above use exactly this "biomarker feedback" model with parents. This is a research and clinical tool; discuss its relevance with a pediatrician or environmental-health provider rather than pursuing consumer-grade testing as a substitute for professional guidance.
What does NOT help
Nothing reduces NNAL directly. Because it is a downstream metabolite with a fixed elimination half-life, there is no "detox" or accelerant that clears it faster; the body processes it on its own pharmacokinetic schedule over 1–3 weeks. The only way to lower it is to lower ongoing NNK exposure.
A negative or low NNAL reading does not mean zero past exposure. Given its multi-week half-life, a single measurement mainly reflects recent exposure; it cannot rule out earlier or intermittent contact with a contaminated environment.
Treating NNAL as if it carries its own hazard classification is a mistake this page previously made. It does not. Concern about NNAL is really concern about NNK exposure — keep that distinction straight when reading other sources on this topic.
Open research questions
- Whether the NNAL-to-cotinine ratio can reliably discriminate thirdhand-only from mixed secondhand/thirdhand exposure in children is an active hypothesis under test in the ADVOCATE cohort, not yet a validated clinical marker. Speculation — pending trial results
- The proposed thirdhand-specific metabolite iso-NNAL has been shown to form in human liver cells in vitro but has not been reliably detected in children's urine in the one published cohort that tested for it, leaving its practical usefulness as a biomarker unresolved. Peer-reviewed — open question
- Whether IARC will ever issue a standalone classification for NNAL, given nearly two decades since Monograph 89 explicitly deferred on it, is unknown; no re-evaluation has been scheduled as of this writing. Speculation
The Embr Exposure Ledger: 4-(Methylnitrosamino)-1-(3-pyridyl)-1-butanol
One chemical, several public questions, answered from independent datasets and joined here — the environment it shows up in, the body burden it carries, how it is regulated, and what actually reduces it.
Detection and body-burden figures are occurrence data, not a personal measurement or a health diagnosis. Part of the Embr Exposure Ledger — an open, cross-dataset chemical join (download the data), reusable with attribution.
Citations
- IARC Working Group on the Evaluation of Carcinogenic Risks to Humans. Smokeless Tobacco and Some Tobacco-specific N-Nitrosamines. IARC Monographs on the Evaluation of Carcinogenic Risks to Humans, Vol. 89 (2007). NBK326484 — classifies NNK and NNN as Group 1; explicitly excludes NNAL and iso-NNAL from the evaluation. Regulatory
- California Office of Environmental Health Hazard Assessment. Proposition 65 list and NNK chemical record (CAS 64091-91-4). OEHHA Regulatory
- Hecht SS, Ye M, Carmella SG, et al. (2001). Metabolites of a tobacco-specific lung carcinogen in the urine of elementary school-aged children. Cancer Epidemiology, Biomarkers & Prevention, 10(11):1109-1116. PMID 11700257 Peer-reviewed
- Thomas JL, Guo H, Carmella SG, Balbo S, Han S, Davis A, Yoder A, Murphy SE, Hecht SS, et al. (2011). Metabolites of a Tobacco-Specific Lung Carcinogen in Children Exposed to Secondhand or Thirdhand Tobacco Smoke in Their Homes. Cancer Epidemiology, Biomarkers & Prevention, 20(6):1213-1221. DOI DOI 10.1158/1055-9965.epi-10-1027 Peer-reviewed — 90% of children in smoker households had detectable urinary NNAL; proposed thirdhand marker iso-NNAL not detected
- Jacob P, Havel C, Lee DH, Yu L, Eisner MD, Benowitz NL (2008). Subpicogram per milliliter determination of the tobacco-specific carcinogen metabolite 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanol in human urine using liquid chromatography-tandem mass spectrometry. Analytical Chemistry, 80(21):8115-8121. DOI 10.1021/ac8009005 Peer-reviewed
- Goniewicz ML, Havel CM, Peng MW, et al. (2009). Elimination kinetics of the tobacco-specific biomarker and lung carcinogen 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanol. Cancer Epidemiology, Biomarkers & Prevention, 18(12):3421-3425. DOI 10.1158/1055-9965.EPI-09-0874 Peer-reviewed
- Wei B, Blount BC, Xia B, Wang L (2016). Assessing exposure to tobacco-specific carcinogen NNK using its urinary metabolite NNAL measured in US population: 2011-2012. Journal of Exposure Science & Environmental Epidemiology, 26(3):249-256. DOI 10.1038/jes.2014.88 Peer-reviewed
- Park EY, et al. (2021). Relationship Between Urinary 4-(Methylnitrosamino)-1-(3-Pyridyl)-1-Butanol and Lung Cancer Risk in the General Population: A Community-Based Prospective Cohort Study. DOI 10.3389/fonc.2021.611674 Peer-reviewed
- Mahabee-Gittens EM, Matt GE, Lopez-Galvez N, Hoh E, Quintana PJE, Dodder NG, Jandarov RA, Stone L, Wullenweber CA, Ahluwalia JS, Merianos AL, et al. (2025). Assessment, detection, and validation of clinical associations of thirdhand smoke exposure (ADVOCATE) study protocol. Pediatric Research, 98(3):864-870. DOI 10.1038/s41390-025-03915-3 Peer-reviewed — measures urinary NNAL and the NNAL/cotinine ratio as a candidate thirdhand-smoke-specific marker in 1,013 children
- Merianos AL, Jandarov RA, Mahabee-Gittens EM (2022). Carcinogenic and tobacco smoke-derived particulate matter biomarker uptake and associated healthcare patterns among children. Pediatric Research, 93:143-153. DOI 10.1038/s41390-022-02031-w Peer-reviewed — higher urinary NNAL and NNAL/cotinine ratio associated with increased urgent-care visits in children
- Sleiman M, Gundel LA, Pankow JF, Jacob P III, Singer BC, Destaillats H (2010). Formation of carcinogens indoors by surface-mediated reactions of nicotine with nitrous acid, leading to potential thirdhand smoke hazards. PNAS, 107(15):6576-6581. DOI 10.1073/pnas.0912820107 Peer-reviewed
Frequently asked questions
Is NNAL classified as a carcinogen by IARC?
No — not on its own, and this is worth stating precisely because the two are often conflated. IARC Monographs Volume 89 (2007), the review that classified NNK and NNN as Group 1 (carcinogenic to humans), explicitly states that NNAL "have not been considered in the present evaluation" due to limited data available at the time. NNAL has never received its own IARC Group classification. The Group 1 finding belongs to its parent compound, NNK. NNAL is included in this Atlas because it is the standard biomarker used to measure NNK exposure — not because it independently carries a hazard classification.
If NNAL isn't classified, why does it matter?
Because it is the tool researchers use to prove that NNK exposure — including thirdhand-smoke exposure from contaminated bedding — actually reaches a person's bloodstream. NNAL is formed when the body metabolizes NNK (via carbonyl reduction), then excreted in urine. Its presence in a nonsmoker, especially a child, is direct biochemical evidence that the person absorbed a dose of the parent carcinogen. Multiple pediatric studies, including a 2011 Cancer Epidemiology, Biomarkers & Prevention study and the ongoing ADVOCATE cohort, use urinary NNAL for exactly this purpose.
Does NNAL itself appear on bedding or in house dust?
Not meaningfully. NNAL is a metabolite formed inside the human body after NNK exposure — it is not a compound that off-gasses from mattresses or accumulates on pillowcases the way NNK or nicotine does. It shows up in urine, not in dust. The compound actually present in thirdhand-smoke-contaminated bedrooms is the parent NNK, which surfaces re-form from deposited nicotine reacting with indoor nitrous acid.
Can NNAL distinguish thirdhand smoke from secondhand smoke exposure in children?
This is an active, evolving research question — not a settled one. Total NNAL is well established as a marker of NNK uptake generally, from any tobacco-smoke route. A 2011 study (Thomas, Hecht, and colleagues) tested a proposed thirdhand-smoke-specific metabolite, iso-NNAL, in children with confirmed secondhand-smoke exposure and did not detect it, concluding the children's exposure in that cohort was via secondhand smoke, not thirdhand smoke. More recent pediatric research (the ADVOCATE study, 2025 protocol) is testing whether the ratio of NNAL to cotinine can help separate thirdhand-only from mixed exposure in children — but that specific discriminating use is still being validated, not yet a settled clinical tool.
Related compounds
This page describes documented biomarker science and does not provide medical advice. Anyone considering biomarker testing for themselves or a child should discuss it with a pediatrician or environmental-health provider for clinical interpretation.
Last reviewed 2026-07-07. If you find a factual error, contact us.