# 1,4-Dichlorobenzene

**p-Dichlorobenzene** (1,4-dichlorobenzene, CASRN 106-46-7) is a colorless to white crystalline solid with a strong pungent, mothball-like odor, used mainly as a moth repellent and space deodorant and as an industrial chemical intermediate.<sup>[1](https://www.epa.gov/assessing-and-managing-chemicals-under-tsca/risk-evaluation-p-dichlorobenzene)</sup><sup> • </sup><sup>[2](https://www.cdc.gov/niosh/npg/npgd0190.html)</sup> It was first produced commercially in the United States in 1915.<sup>[3](https://riss.aist.go.jp/en/research-outcomes/360/)</sup> Reported production volume in the 2016 Chemical Data Reporting was between 50 million and 100 million lbs per year.<sup>[1](https://www.epa.gov/assessing-and-managing-chemicals-under-tsca/risk-evaluation-p-dichlorobenzene)</sup>

| Key fact | Detail |
|---|---|
| Identity | CASRN 106-46-7; formula C₆H₄Cl₂; molecular weight 147.0; synonyms p-DCB, para-dichlorobenzene, Dichlorocide, Paracide<sup>[2](https://www.cdc.gov/niosh/npg/npgd0190.html)</sup> |
| Physical behavior | Melting point 128°F, boiling point 345°F, vapor pressure 1.3 mmHg; a combustible solid that readily sublimates at room temperature<sup>[2](https://www.cdc.gov/niosh/npg/npgd0190.html)</sup><sup> • </sup><sup>[1](https://www.epa.gov/assessing-and-managing-chemicals-under-tsca/risk-evaluation-p-dichlorobenzene)</sup> |
| Main uses | Moth repellent and space deodorant for toilets and refuse containers; intermediate for 2,5-dichloroaniline and polyphenylene sulfide resins<sup>[4](https://www.ncbi.nlm.nih.gov/books/NBK234168/)</sup><sup> • </sup><sup>[3](https://riss.aist.go.jp/en/research-outcomes/360/)</sup> |
| Carcinogen classifications | IARC Group 2B (possibly carcinogenic to humans); NTP "reasonably anticipated to be a human carcinogen"; EPA 2026 draft evaluation: not likely to be carcinogenic to humans<sup>[5](https://www.sciencedirect.com/science/article/abs/pii/S0048969721020581)</sup><sup> • </sup><sup>[6](https://www.ncbi.nlm.nih.gov/books/NBK590902/)</sup><sup> • </sup><sup>[1](https://www.epa.gov/assessing-and-managing-chemicals-under-tsca/risk-evaluation-p-dichlorobenzene)</sup> |
| Workplace limits | OSHA PEL 75 ppm (450 mg/m³) 8-hour TWA; NIOSH IDLH 150 ppm; ACGIH TLV 10 ppm<sup>[2](https://www.cdc.gov/niosh/npg/npgd0190.html)</sup><sup> • </sup><sup>[7](https://www.cdc.gov/niosh/idlh/106467.html)</sup> |
| Typical exposure | Average daily adult intake about 35 µg, mainly from breathing vapors of household products; more than 95% of absorbed DCB leaves the body in urine within a week<sup>[8](https://wwwn.cdc.gov/TSP/PHS/PHS.aspx?phsid=702&toxid=126)</sup> |
| Regulatory status | EPA drinking water MCLG and MCL of 0.075 mg/L; EPA chronic inhalation reference concentration 800 µg/m³; Japan lifetime indoor guideline 240 µg/m³<sup>[9](https://nepis.epa.gov/Exe/ZyPURL.cgi?Dockey=P1010FFC.TXT)</sup><sup> • </sup><sup>[10](https://pmc.ncbi.nlm.nih.gov/articles/PMC3501547/)</sup> |

## Physical and chemical properties

p-Dichlorobenzene is one of the three dichlorobenzene isomers, each consisting of two chlorine atoms attached to one benzene ring. It is a colorless or white crystalline solid with a molecular weight of 147.0, a melting point of 128°F, a boiling point of 345°F, and a vapor pressure of 1.3 mmHg.<sup>[2](https://www.cdc.gov/niosh/npg/npgd0190.html)</sup> It is practically insoluble in water and is a combustible solid, though it may take some effort to ignite; its lower explosive limit is 2.5%.<sup>[2](https://www.cdc.gov/niosh/npg/npgd0190.html)</sup>

Sublimation is the defining behavior for its use and its exposure profile: when a package is opened, the solid slowly changes into a vapor that acts as a deodorizer and insect killer, and over 90% of its use involves vapor production by sublimation.<sup>[4](https://www.ncbi.nlm.nih.gov/books/NBK234168/)</sup><sup> • </sup><sup>[8](https://wwwn.cdc.gov/TSP/PHS/PHS.aspx?phsid=702&toxid=126)</sup> Most people begin to smell it in air at about 0.18 ppm.<sup>[8](https://wwwn.cdc.gov/TSP/PHS/PHS.aspx?phsid=702&toxid=126)</sup>

## Production and uses

Commercial production chlorinates benzene or chlorobenzene at high temperature in the presence of catalysts; isomeric mixtures from the process yield about 75% para-dichlorobenzene, 25% ortho-dichlorobenzene, and 0.2% meta-dichlorobenzene.<sup>[4](https://www.ncbi.nlm.nih.gov/books/NBK234168/)</sup><sup> • </sup><sup>[11](https://www.ncbi.nlm.nih.gov/books/NBK402158/)</sup>

Historically, use split roughly between deodorizing and pest control: one estimate put 50% of use as space deodorant and sanitizer in toilets and refuse containers, 40% in moth control, and 10% in other applications, with total U.S. use in 1972 estimated at 68 million pounds.<sup>[4](https://www.ncbi.nlm.nih.gov/books/NBK234168/)</sup> Other applications include an insecticide for fruit borers and ants, mold and mildew control on tobacco seed beds, leather, and fabrics, and use as an intermediate in the manufacture of 2,5-dichloroaniline, dyes, pharmaceuticals, and [polyphenylene sulfide](https://www.edgepedia.org/polyphenylene-sulfide) resins.<sup>[9](https://nepis.epa.gov/Exe/ZyPURL.cgi?Dockey=P1010FFC.TXT)</sup><sup> • </sup><sup>[3](https://riss.aist.go.jp/en/research-outcomes/360/)</sup> In the United States, most mothball products are made of essentially pure p-dichlorobenzene, which avoids the flammability hazard associated with naphthalene.<sup>[12](https://pmc.ncbi.nlm.nih.gov/articles/PMC2922736/)</sup>

## Indoor exposure

Because the products are nearly pure p-DCB and release vapor continuously, indoor air is the main route of general-population exposure. Reported levels in some homes and public restrooms have ranged from 0.291 to 272 ppb of air, while outdoor levels range from 0.01 to 1 ppb.<sup>[8](https://wwwn.cdc.gov/TSP/PHS/PHS.aspx?phsid=702&toxid=126)</sup> The average daily adult intake is about 35 µg, coming mainly from breathing vapors released by products in homes and businesses.<sup>[8](https://wwwn.cdc.gov/TSP/PHS/PHS.aspx?phsid=702&toxid=126)</sup>

**Emission behavior depends on placement and temperature.** In chamber and test-house measurements, emission rates varied considerably between p-DCB products, primarily due to product packaging, and were generally suppressed when products were used in closed closets or garment bags relative to well-ventilated chambers; typical variations in home air temperature significantly influence emission rates.<sup>[13](https://pubmed.ncbi.nlm.nih.gov/23019821/)</sup> Concentrations in bedrooms adjacent to closets where moth repellents are used can exceed or approach odor thresholds.<sup>[13](https://pubmed.ncbi.nlm.nih.gov/23019821/)</sup> Based on whole-house emission rates from a previous study, somewhere between 2% and 12% of homes had active p-DCB sources.<sup>[13](https://pubmed.ncbi.nlm.nih.gov/23019821/)</sup> In a sample of Japanese children, inhalation at home contributed 30% of daily p-DCB intake, and airborne p-DCB levels and its metabolite were higher than those reported for other countries, leading the authors to call for further reduction of airborne p-DCB in Japanese houses.<sup>[5](https://www.sciencedirect.com/science/article/abs/pii/S0048969721020581)</sup> Moth repellent chemicals also deposit on stored clothing: a regular cotton shirt indirectly exposed in a storage cabinet can contain up to 7 mg of p-dichlorobenzene even after one hour of airing.<sup>[14](https://pubmed.ncbi.nlm.nih.gov/18063007/)</sup>

## Health effects and carcinogenicity classifications

Breathing p-DCB vapor can irritate the eyes, nose, and throat and cause dizziness, headache, and upset stomach; breathing or swallowing very large amounts can cause liver damage.<sup>[15](https://wwwn.cdc.gov/Tsp/MMG/MMGDetails.aspx?mmgid=1206&toxid=126)</sup> In the body, p-DCB is metabolized mainly to 2,5-dichlorophenol, which is excreted mostly in urine; more than 95% of absorbed DCB leaves the body in urine within a week, with small amounts in feces and exhaled air and tiny amounts retained in fat.<sup>[8](https://wwwn.cdc.gov/TSP/PHS/PHS.aspx?phsid=702&toxid=126)</sup> Reported effects in people with very high or prolonged exposure include dizziness, headaches, liver problems, skin blotches, and anemia; exposure has also been reported to induce allergic purpura and has been related to increased white blood cell counts and blood urea nitrogen levels.<sup>[8](https://wwwn.cdc.gov/TSP/PHS/PHS.aspx?phsid=702&toxid=126)</sup><sup> • </sup><sup>[5](https://www.sciencedirect.com/science/article/abs/pii/S0048969721020581)</sup>

**Carcinogenicity classifications differ among agencies.** The International Agency for Research on Cancer classifies p-DCB in Group 2B, possibly carcinogenic to humans.<sup>[5](https://www.sciencedirect.com/science/article/abs/pii/S0048969721020581)</sup> The National Toxicology Program's 15th Report on Carcinogens lists 1,4-dichlorobenzene as reasonably anticipated to be a human carcinogen, first listed in 1989, based on sufficient evidence from studies in experimental animals: oral exposure caused liver tumors in mice, kidney cancer and mononuclear-cell leukemia in male rats, and later inhalation studies caused liver cancer in mice of both sexes; human data are inadequate to evaluate the relationship.<sup>[6](https://www.ncbi.nlm.nih.gov/books/NBK590902/)</sup> In its August 2026 draft risk evaluation under the Toxic Substances Control Act, the EPA determined that p-dichlorobenzene is not likely to be carcinogenic to humans, while identifying respiratory toxicity, liver toxicity, developmental toxicity, and neurotoxicity as the primary non-cancer hazards.<sup>[1](https://www.epa.gov/assessing-and-managing-chemicals-under-tsca/risk-evaluation-p-dichlorobenzene)</sup> NIOSH considers p-dichlorobenzene a potential occupational carcinogen and recommends the most protective respirators at any detectable concentration.<sup>[7](https://www.cdc.gov/niosh/idlh/106467.html)</sup>

## Regulation and risk evaluation

Workplace limits reflect this range of judgment: OSHA's permissible exposure limit is 75 ppm (450 mg/m³) as an 8-hour time-weighted average, the NIOSH immediately dangerous to life or health concentration is 150 ppm, and the ACGIH threshold limit value is 10 ppm.<sup>[2](https://www.cdc.gov/niosh/npg/npgd0190.html)</sup><sup> • </sup><sup>[7](https://www.cdc.gov/niosh/idlh/106467.html)</sup> For drinking water, EPA set a maximum contaminant level goal and maximum contaminant level of 0.075 mg/L.<sup>[9](https://nepis.epa.gov/Exe/ZyPURL.cgi?Dockey=P1010FFC.TXT)</sup> EPA lists a non-cancer chronic inhalation reference concentration of 800 µg/m³, and Japan has specified a guideline value for lifetime exposure of 240 µg/m³.<sup>[10](https://pmc.ncbi.nlm.nih.gov/articles/PMC3501547/)</sup>

In August 2026, EPA released a draft risk evaluation under TSCA preliminarily determining that p-dichlorobenzene presents an unreasonable risk of injury to human health, driven by risks to workers from 7 evaluated conditions of use, to occupational non-users from 5 of those conditions, and to consumers associated with air care products; the findings for workers do not reflect use of personal protective equipment. As a preliminary finding, the EPA found that the conditions of use under evaluation posed no significant contribution to unreasonable risk either to the general population, including those living near facility fencelines, or to the environment.<sup>[1](https://www.epa.gov/assessing-and-managing-chemicals-under-tsca/risk-evaluation-p-dichlorobenzene)</sup> Because the solid readily sublimates at room temperature, inhalation is the key exposure pathway in the assessment.<sup>[1](https://www.epa.gov/assessing-and-managing-chemicals-under-tsca/risk-evaluation-p-dichlorobenzene)</sup>

## Clinical distinction from naphthalene

Household deodorizers and moth repellents contain either paradichlorobenzene or naphthalene compressed into a solid ball or other shape, and naphthalene is medically the more important toxin, with hematologic and nervous system effects.<sup>[16](https://pubmed.ncbi.nlm.nih.gov/8355318/)</sup> In a screening of 10 products by two radiologists, paradichlorobenzene-containing products were consistently strongly radiopaque (blocks X-rays, so it shows up white on radiographs) while naphthalene-containing products were radiolucent, so an abdominal radiograph can distinguish which product has been ingested; the halogen in the chemical structure is thought to account for the radiopacity.<sup>[16](https://pubmed.ncbi.nlm.nih.gov/8355318/)</sup> ATSDR likewise notes that because 1,4-dichlorobenzene is radiopaque, x-rays can be used to assess suspected ingestion.<sup>[15](https://wwwn.cdc.gov/Tsp/MMG/MMGDetails.aspx?mmgid=1206&toxid=126)</sup>

## References

1. [Risk Evaluation for p-Dichlorobenzene, US EPA](https://www.epa.gov/assessing-and-managing-chemicals-under-tsca/risk-evaluation-p-dichlorobenzene)
2. [p-Dichlorobenzene, NIOSH Pocket Guide to Chemical Hazards, CDC](https://www.cdc.gov/niosh/npg/npgd0190.html)
3. [p-Dichlorobenzene: Abstract, Research Institute of Science for Safety and Sustainability, AIST](https://riss.aist.go.jp/en/research-outcomes/360/)
4. [p-Dichlorobenzene, in Drinking Water and Health, NCBI Bookshelf](https://www.ncbi.nlm.nih.gov/books/NBK234168/)
5. [Estimating household exposure to moth repellents p-dichlorobenzene and naphthalene and the relative contribution of inhalation pathway in a sample of Japanese children, Science of The Total Environment](https://www.sciencedirect.com/science/article/abs/pii/S0048969721020581)
6. [1,4-Dichlorobenzene, 15th Report on Carcinogens, NCBI Bookshelf](https://www.ncbi.nlm.nih.gov/books/NBK590902/)
7. [p-Dichlorobenzene, IDLH Documentation, NIOSH, CDC](https://www.cdc.gov/niosh/idlh/106467.html)
8. [Dichlorobenzenes, Public Health Statement, ATSDR](https://wwwn.cdc.gov/TSP/PHS/PHS.aspx?phsid=702&toxid=126)
9. [Technical Factsheet on p-Dichlorobenzene, US EPA](https://nepis.epa.gov/Exe/ZyPURL.cgi?Dockey=P1010FFC.TXT)
10. [Concentrations and Risks of p-Dichlorobenzene in Indoor and Outdoor Air, PMC](https://pmc.ncbi.nlm.nih.gov/articles/PMC3501547/)
11. [Dichlorobenzenes: Production and use, NCBI Bookshelf](https://www.ncbi.nlm.nih.gov/books/NBK402158/)
12. [A Critical Review of Naphthalene Sources and Exposures Relevant to Indoor and Outdoor Air, PMC](https://pmc.ncbi.nlm.nih.gov/articles/PMC2922736/)
13. [Emissions of p-dichlorobenzene and naphthalene from consumer products, PubMed](https://pubmed.ncbi.nlm.nih.gov/23019821/)
14. [Domestic sampling: exposure assessment to moth repellent products using ultrasonic extraction and capillary GC-MS, PubMed](https://pubmed.ncbi.nlm.nih.gov/18063007/)
15. [1,4-Dichlorobenzene, Medical Management Guidelines, ATSDR](https://wwwn.cdc.gov/Tsp/MMG/MMGDetails.aspx?mmgid=1206&toxid=126)
16. [Radiopacity of household deodorizers, air fresheners, and moth repellents, PubMed](https://pubmed.ncbi.nlm.nih.gov/8355318/)

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*Topic: Encyclopedia › Life and health › Applied biology and nonhuman health › Plant disease and plant protection › Pesticides*

*Initially written Oct 20, 2026*

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License: Edgepedia Community License 1.0, https://www.edgepedia.org/edgepedia/license