POOR Active Ingredient NOAEL Data GHS Classified Sensitization Data Dermal Penetration

Hydroquinone

Also known as: 1,4-Benzenediol, Dihydroxybenzene, Benzene, p-dihydroxy-, Black and White Bleaching Cream, Derma-Blanch (+14 more)

INCI: HYDROQUINONE

Hydroquinone (CAS 123-31-9) is a cosmetic active ingredient functioning as Tyrosinase inhibitor; competitive inhibitor and cytotoxic agent to melanocytes;. NOAEL 20 mg/kg bw/day (cross-referenced against ToxValDB ECHA IUCLID); EU Regulation 1223/2009 status: prohibited. Industrial safety data is also available in the chemical safety database. Same-CAS public records also appear in industrial chemical safety and pharmaceutical data.

View industrial chemical safety profile for CAS 123-31-9 →

CAS Number
123-31-9
View industrial chemical safety profile →
Function
Tyrosinase inhibitor; competitive inhibitor and cytotoxic agent to melanocytes; inhibits both melanin synthesis and DNA synthesis in melanocytes; benchmark for all modern depigmenting actives
Editorial assessment
POOR
Preliminary editorial note — not a computed safety verdict.

Chemistry & Identifiers

EC Number
204-617-8
ChEBI: CHEBI:17594 UNII: XV74C1N1AE Wikidata: Q419164

Regulatory Status

EU EU Status prohibited
US US Status restricted
US Notes Reclassified from OTC to prescription-only under MoCRA/CARES Act 2020. FDA has not issued final Rx rule; interim: OTC products without NDA receive warning letters. CIR concluded safe at ≤1% in rinse-off only. Rx 4% available under physician supervision. Saudi Arabia 2025 study found HQ in 80% of unregulated skin-lightening samples despite prescription restrictions. Banned or Rx-only in Japan, Australia, New Zealand, and multiple African and Asian markets.

For full compliance data across multiple jurisdictions, use the Substance Compliance tool.

Safety Data

Margin of Safety, dermal absorption, and sensitization profile summaries for Hydroquinone.

Calculate MoS for your specific formulation with the MoS Calculator.

Toxicological Studies

10 study endpoints found for Hydroquinone. NOAEL (No Observed Adverse Effect Level) values are used to calculate the Margin of Safety per SCCS methodology.

Endpoint Value Route Species Study Type Source
NOAEL =3840 mg/kg dermal rat general toxicity CIR Safety Assessment
NOAEL =3840 mg/kg dermal rat general toxicity CIR Safety Assessment
NOAEL =3840 mg/kg dermal rat general toxicity CIR Safety Assessment
NOAEL =3840 mg/kg dermal rat general toxicity CIR Safety Assessment
NOAEL =4800 mg/kg dermal mouse general toxicity CIR Safety Assessment
NOAEL =4800 mg/kg dermal mouse general toxicity CIR Safety Assessment
NOAEL =4800 mg/kg dermal mouse general toxicity CIR Safety Assessment
NOAEL =4800 mg/kg dermal mouse general toxicity CIR Safety Assessment
NOAEL =73.9 mg/kg bw/day dermal Rat subchronic ECHA
NOAEL =109.6 mg/kg bw/day dermal Rat subchronic ECHA

GHS Hazard Classification

Globally Harmonized System classification per ECHA C&L inventory and ILO/WHO International Chemical Safety Cards.

Short-term Exposure Effects
The substance is severely irritating to the eyes. The substance is irritating to the skin and respiratory tract.
Long-term Exposure Effects
Repeated or prolonged contact with skin may cause dermatitis. Repeated or prolonged contact may cause skin sensitization. The substance may have effects on the eyes and skin. This may result in discolouration of the conjunctiva and cornea and skin depigmentation. This substance is possibly carcinogenic to humans.
Routes of Exposure
The substance can be absorbed into the body by inhalation, through the skin and by ingestion.

Pre-Calculated Safety Assessment

Pre-calculated NOAEL → SED → MoS audit trail for Hydroquinone across SCCS product categories, with measured dermal absorption where available.

Sensitization Profile

Contact sensitization data for Hydroquinone based on clinical patch test studies and IFRA standards.

Sensitization Rate
low
Allergen Class
dye
EU Allergen Listed
no
Patch Test Positive Rate
0.3%
Cross-reactivity Group
para-amino-group
Reaction Type
contact-dermatitis

Source: IVDK; NACDG; ESSCA

Dermal Penetration Profile

Skin absorption and penetration characteristics of Hydroquinone, relevant to systemic exposure and MoS calculations.

Absorption %
35-50%
Penetration Level
dermis
Penetration Depth
epidermis/dermis
Molecular Weight
110.1 Da
Log P
0.59
Systemic Absorption
yes
Topical Bioavailability
25-45%
Safety Margin Factor
very-high
Vehicle Dependent
Yes — absorption varies by formulation

Source: SCCS Opinion

EPA ToxValDB — Toxicity Values

10 toxicity values from EPA ToxValDB (aggregated from CCTE, HPV, ToxRefDB, IRIS, and other regulatory dossiers).

Endpoint Value Species Route Duration Source
LOEL =64 mg/kg-day Rat oral chronic ECOTOX
NOEL =20 mg/kg-day Rat oral chronic ECOTOX
NOEL =120 mg/kg-day Mouse oral short-term ECOTOX
LD50 =320 mg/kg Rat oral acute NIOSH IDLH
LD50 =200 mg/kg Dog oral acute NIOSH IDLH
LD50 =70 mg/kg Cat oral acute NIOSH IDLH
NOEL =150 mg/kg-day Rat oral chronic ECOTOX
NOEL =150 mg/kg-day Rat oral chronic ECOTOX
NOEL =15 mg/kg-day Rat oral chronic ECOTOX
NOEL =150 mg/kg-day Rat oral chronic ECOTOX

IARC Carcinogenicity

International Agency for Research on Cancer (WHO) monograph evaluation.

IARC Group
3
Volume
15, Sup 7, 71
Evaluation Year
1998

EU CLP Annex VI Harmonized Classification

Legally binding harmonized classification per Regulation (EC) No 1272/2008 (CLP) Annex VI.

Signal Word
Danger
Pictograms
Health HazardHarmful / IrritantCorrosiveEnvironmental Hazard
Hazard Class and Category
Carc. 2; Muta. 2; Acute Tox. 4 *; Eye Dam. 1; Skin Sens. 1; Aquatic Acute 1
Hazard Statements
  • H351 Suspected of causing cancer
  • H341 Suspected of causing genetic defects
  • H302 Harmful if swallowed
  • H318 Causes serious eye damage
  • H317 May cause an allergic skin reaction
  • H400 Very toxic to aquatic life
Specific Concentration Limits / M-factors
M = 10

Inserted via ATP: ATP01

Sensitization AOP Dashboard

Adverse Outcome Pathway data across 5 assays (DPRA, KeratinoSens, hCLAT, LLNA, NESIL) aggregated from public sources.

DPRA Cys %
91.45%
DPRA Lys %
52.4%
KeratinoSens IC50
130.73 µM
hCLAT CV75
5 µg/mL
LLNA EC3
0.12%
NESIL
30 µg/cm²
LLNA: Strong (1A) GHS: 1A

Source: LLNA: Lea (1999) | Kimber et al. (1998); DPRA: Natsch et al. 2013 [DOI:10.1002/jat.2868] | Nukada et al. 2013 [DOI:10.1016/j.tiv.2012.11.006]; KS: Natsch et al. 2013 [DOI:10.1002/jat.2868]; hCLAT: Ashikaga et al. 2010 [DOI:10.1177/026119291003800403] | Sakaguchi et al. 2010 [DOI:10.1016/j.tiv.2010.05.012]

Endocrine Disruptor Evidence (Expanded)

Cross-referenced EDC classifications, mechanism data, and dose-response evidence from EDLists, SIN List, and cosmetic-specific detail sources.

Cosmetic-Specific Mechanism
Category: other
Receptor targets: ERα, AhR
LOEC: 1 µM
EU status: banned in cosmetics (Annex II)

modulator; aryl hydrocarbon receptor agonist

ECHA REACH Registration

European Chemicals Agency REACH dossier and Substances of Very High Concern listing.

Registration Type
Full
Tonnage Band
10,000 - 100,000 tonnes
Substance Type
SUBSTANCE
SVHC Candidate
No
Hazard classification: Restricted (Annex XVII)

EU CosIng Annex Listing

European Commission CosIng database Annex references per Regulation (EC) No 1223/2009.

Annex II — Prohibited
Ref: 1339
(EC) 2013/344
CMR: Carcinogenic Cat. 2(),Mutagenic Cat. 2()

Expanded Jurisdictional Detail

Additional regulatory detail beyond the 7-jurisdiction summary: Saudi SFDA, Korea MFDS, ASEAN ACD, Japan/Korea, Brazil/India, and cross-jurisdictional restriction entries.

SA Saudi SFDA (II - Prohibited)
ASEAN Cosmetic Directive (II)
Ref: 1339
JPKR Japan/Korea Cosmetics
Korea (Prohibited): ; Category: General
Korea (Restricted): max 2%
BRIN Brazil/India Cosmetics
Brazil: Prohibited
India: Prohibited (GNRAS)
India: Restricted · max 0.02% (after mixing for use)
Additional Jurisdictional Restrictions (10)
Jurisdiction Status Max % Product Type
CN banned - -
CN restricted 0.3 Oxidative hair dye products only
CN permitted_hair_dye 0.3 Oxidative hair dye ONLY
IN banned - all OTC cosmetics — drug classification
IN drug_classification - skin-lightening / fairness products
AU restricted 2.0 skin lightening
GCC banned - All cosmetics
SA banned - All cosmetic products

Expanded Dermal Absorption Data

Cross-database dermal penetration: EPA Dryad physics-based, Roberts Mendeley permeation, and SCCS-aggregated measured values.

EPA Dryad Skin Absorption (physics-based)
MW: 110.111
LogP: 1.61078
Kp epidermis: 0.00383 cm/h
% dose epidermis: 0.97%
% dose stratum corneum: 1.14%
% dose dermis: 0.93%

Source: EPA Dryad Skin Absorption 2024

Roberts Skin Permeation (Mendeley 2022)
MW: 110.11
Log Kow: 0.62
Log Kp: -5.0301183562535
Log Jmax: -9.129441012722962

Source: Roberts Cheruvu Mendeley 2022

Aggregated DA Values (2 records across 5 sources)
Type DA % Method Skin Model SCCS Ref
measured_in_vitro 11.0 In vivo — clinical (urine excretion) In vitro — Franz cells - Bucks et al. 1988; CIR Amended SA 2014 (1988)
measured_in_vitro 42.5 - - SCCS/1444/11

Function Categories & List Membership

Cosmetic/Chemical Function Categories
Antioxidant Bleaching agent Dye Flavouring and nutrient Fragrance Monomers Reducing agent Stabilizing agent
Regulatory List Membership (3)
EU Banned in Cosmetics FDA Indirect Food Contact Additives EU CosIng Cosmetics Ingredient Database

Editorial summary

Preliminary editorial summary for Hydroquinone — not a computed safety verdict. See the sourced toxicological data above.

Regulatory Flags

eu-banned annex-ii-prohibited us-prescription-only cares-act-2020 rx-4pct-us ochronosis-risk leukoderma-risk cytotoxic carcinogenicity-concern mutagenicity-concern para-benzoquinone-intermediate banned-japan-australia-nz benchmark-only not-for-cosmetic-formulation avoid minamata-public-health-concern endocrine_disruptor eu_banned_cosmetics eu_cosing_listed

NOAEL Studies Summary

View details ->

Public NOAEL study rows linked to Hydroquinone by CAS number or substance name.

Studies
12
Lowest NOAEL
73.9
Highest NOAEL
4800

Units vary across source rows: mg/kg bw/day, mg/kg

ECHA CIR Safety Assessment

Dermal Absorption

View details ->
Absorption % Method Vehicle
11.0 In vivo — clinical (urine excretion) In vitro — Franz cells Aqueous solution (in vivo); Various
42.5 - -

Known Synonyms

1,4-Benzenediol Dihydroxybenzene Benzene, p-dihydroxy- Black and White Bleaching Cream Derma-Blanch EINECS 204-617-8 Hidroquinone NCI-C55834 para-Dihydroxybenzene para-Dioxybenzene para-Hydroquinone Pyrogentistic acid Tequinol USAF EK-356 1,4-Dihydroxy-benzeen UNII-XV74C1N1AE Epiquin Sunvanish 1,4-Dihydroxy-benzol

Chemical Function

Stabilizing agent Antioxidant Fragrance Dye Reducing agent Bleaching agent Flavouring and nutrient Monomers

Regulatory Lists

banned; Europe; Personal care CEDI Indirect additives food contact (10/2018) Australia; Food and drug - smoking-related products Europe; Personal care; restricted Canada; pharmaceutical Canada; pharmaceutical Danish Environmental Protection Agency Personal care; Southeast Asia Europe; Food contact items; Toys and children's products Europe inert_ingredient; non_food_use; Pesticides drinking_water; Europe; manufacturing; plastic_additive

Australian Status

AICIS status: listed

Cross-Vertical Safety Context

Same-CAS public records found in pharmaceutical data.

SOURCE ChEMBL / DrugCentral / FAERS DB_PHARMA CAS match

Pharmaceutical Data

Same-CAS rows from the pharmaceutical spoke database.

Compound
HYDROQUINONE
ChEMBL ID
CHEMBL537
Max Phase
4
Adverse Event Associations
55
View full pharmaceutical profile →

Frequently Asked Questions

Is Hydroquinone safe in cosmetics?

Hydroquinone has a safety rating of "POOR" in our database. EU status: prohibited. US status: restricted. 10 toxicological study endpoint(s) are available in our database.

Is Hydroquinone allowed in the EU?

Hydroquinone EU regulatory status: prohibited. This is based on EU Regulation 1223/2009 and its amendments.

What does Hydroquinone do in cosmetics?

Hydroquinone functions as: Tyrosinase inhibitor; competitive inhibitor and cytotoxic agent to melanocytes; inhibits both melanin synthesis and DNA synthesis in melanocytes; benchmark for all modern depigmenting actives. It is classified as a Active Ingredient in our database. CAS number: 123-31-9.

What is the NOAEL for Hydroquinone?

The NOAEL (No Observed Adverse Effect Level) for Hydroquinone is =3840 mg/kg based on a general toxicity study via dermal route in rat. A total of 10 study endpoints are available. Source: CIR Safety Assessment.

Is Hydroquinone used outside cosmetics?

Hydroquinone also appears in industrial chemical safety and pharmaceutical data. The cross-vertical cards on this page render same-CAS public rows from the matched databases.

Does Hydroquinone have different safety status in cosmetics vs industrial chemicals?

Hydroquinone is prohibited in EU cosmetics but has active industrial GHS classifications (H302, H312, H317, H318, H341, H351, H400, H410).

Compliance Tools

Check Hydroquinone compliance across multiple jurisdictions:

Ingredient Decoder
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82 Allergen Checker
Check for EU declarable fragrance allergens
Substance Compliance
Check compliance across multiple jurisdictions
MoS Calculator
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Heavy Metal Limits
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