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Chemical Sampling Information (CSI)
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General Description

Synonyms: Quinol; 1,4-Dihydroxybenzene; 1,4-Benzenediol

OSHA IMIS Code Number: 1490

Chemical Abstracts Service (CAS) Registry Number: 123-31-9

NIOSH Registry of Toxic Effects of Chemical Substances (RTECS) Identification Number: MX3500000

Department of Transportation Regulation Number (49 CFR 172.101) and Guide: 2662 153

NIOSH Pocket Guide to Chemical Hazards, Hydroquinone: chemical description, physical properties, potentially hazardous incompatibilities, and more

Exposure Limits

OSHA Permissible Exposure Limit (PEL):

General Industry: 29 CFR 1910.1000 Table Z-1 -- 2 mg/m3 TWA

Construction Industry: 29 CFR 1926.55 Appendix A -- 2 mg/m3 TWA

Maritime: 29 CFR 1915.1000 Table Z-Shipyards -- 2 mg/m3 TWA

American Conference of Governmental Industrial Hygienists (ACGIH) Threshold Limit Value (TLV): 2 mg/m3 TWA; Appendix A3 - Confirmed Animal Carcinogen with Unknown Relevance to Humans

National Institute for Occupational Safety and Health (NIOSH) Recommended Exposure Limit (REL): 2 mg/m3 Ceiling (15 Minutes)

Health Factors

Carcinogenic Classification:

International Agency for Research on Cancer (IARC): Group 3, not classifiable as to its carcinogenicity to humans [381 KB PDF, 171 pages]

NIOSH Immediately Dangerous To Life or Health Concentration (IDLH): 50 mg/m3

Potential Symptoms: Irritation of eyes: conjunctivitis; keratitis, blurred vision; CNS excitement; green-colored urine; nausea; dizziness; sense of suffocation, rapid breathing; muscle twitches, delirium; collapse; skin irritation, sensitization, dermatitis: INGES. ACUTE: Headache, ringing in the ears, dizziness, nausea, vomiting; shortness of breath; convulsions

Health Effects: Irritation-Skin---Mild (HE16); Cumulative Corneal damage (HE3); Mutagen (HE2); CNS effects (HE7); Suspect Teratogen (HE5)

Affected Organs: Eyes, skin, respiratory system, CNS


  1. Hydroquinone is a metabolite of benzene (via phenol) and is largely excreted in urine as glucuronide and sulfate conjugates.
  2. Hydroquinone has been used topically in skin-lightening products. It reduces the melanin content of melanosomes as a competitive inhibitor/substrate of tyrosinase. A few cases of depigmentation in workers exposed to black-and-white film developer containing hydroquinone have been reported.
  3. Brown staining of conjunctiva and corneas (leading to severe corneal damage with continuous occupational exposure of >5 years) occurred in some hydroquinone production workers before exposure limits were established.

Literature Basis:

  • NIOSH Pocket Guide to Chemical Hazards: Hydroquinone.
  • International Chemical Safety Cards (WHO/IPCS/ILO): Hydroquinone.
  • DeCaprio, A.P.: The toxicology of hydroquinone - relevance to occupational and environmental exposure. Crit. Rev. Toxicol. 29(3): 283-330, 1999.
  • English, J.C. and Deisinger, P.J.: Metabolism and disposition of hydroquinone in Fischer 344 rats after oral or dermal administration. Food Chem. Toxicol. 43(3): 483-493, 2005.
  • Halder, R.M. and Richards, G.M.: Topical agents used in the management of hyperpigmentation. Skin Therapy Lett. 9(6): 1-3, 2004.
  • Pohanish, R.P. (editor): Hydroquinone. Sittig's Handbook of Toxic and Hazardous Chemicals and Carcinogens, Fourth Ed., Vol. 1. Norwich, NY: Noyes Publications, William Andrew Publishing, 2002, pp. 1293-1295.

Date Last Revised: 06/26/2006

Monitoring Methods used by OSHA

Primary Laboratory Sampling/Analytical Method (SLC1):

  • sampling media: Coated XAD-7 (80/40 mg sections; 20/60 mesh) Coating is 10% Phosphoric Acid.
    analytical solvent: Methanol
    maximum volume: 20 Liters
    maximum flow rate: 0.2 L/min
    current analytical method: Gas Chromatography; GC/FID
    method reference: OSHA Analytical Method (OSHA PV2094)
    method classification: Partially Validated

Bulk Method:

  • Limit the amount of bulk submitted to one gram or one mL.

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