Poor Active Ingredient NOAEL Data GHS Classified Sensitization Data Dermal Penetration

Hydroquinone

INCI: HYDROQUINONE

CAS Number
123-31-9
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
Safety Rating
POOR

Regulatory Status

🇪🇺 EU Status prohibited
🇺🇸 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 55 jurisdictions, use the Substance Compliance tool.

Safety Data

Margin of Safety (MoS)
not established
Dermal Absorption
high
Sensitization
high

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
NOEL 4800 mg/kg bw/day dermal code:3543 dermal REACH
LOAEL 50 mg/kg bw/day oral mouse oral REACH
LOAEL 50 mg/kg bw/day oral rat oral REACH
NOEL 3840 mg/kg bw/day dermal rat dermal REACH
NOAEL 73.9 mg/kg bw/day dermal rat dermal REACH
NOAEL 20 mg/kg bw/day oral rat oral REACH
NOAEL 50 mg/kg bw/day oral mouse oral REACH
NOAEL 50 mg/kg bw/day oral rat oral REACH
NOAEL 250 mg/kg bw/day oral rat oral REACH
NOAEL 125 mg/kg bw/day oral mouse oral REACH

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.

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/1444/11

Expert Verdict

Hydroquinone is a historical gold-standard depigmenting agent now prohibited in EU cosmetics and restricted to prescription-only in the US due to unacceptable risk profile including exogenous ochronosis, leukoderma, and potential carcinogenicity; modern alternatives offer superior safety with comparable efficacy.

⚠️
Concern Level: High

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

Frequently Asked Questions

Is Hydroquinone safe in cosmetics?

Hydroquinone is a historical gold-standard depigmenting agent now prohibited in EU cosmetics and restricted to prescription-only in the US due to unacceptable risk profile including exogenous ochronosis, leukoderma, and potential carcinogenicity; modern alternatives offer superior safety with comparable efficacy. The EU classifies Hydroquinone as "prohibited". Safety rating: POOR. 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 Margin of Safety for Hydroquinone?

not established The Margin of Safety (MoS) is calculated using SCCS methodology. A MoS above 100 is generally considered safe. Use the MoS Calculator tool to calculate MoS for your specific formulation and product category.

What is the NOAEL for Hydroquinone?

The NOAEL (No Observed Adverse Effect Level) for Hydroquinone is 4800 mg/kg bw/day based on a dermal study via dermal route in code:3543. A total of 10 study endpoints are available. Source: REACH.

Compliance Tools

Check Hydroquinone compliance across multiple jurisdictions:

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Ingredient Decoder
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82 Allergen Checker
Check for EU declarable fragrance allergens
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Substance Compliance
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MoS Calculator
Calculate Margin of Safety using SCCS methodology
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Heavy Metal Limits
Compare limits across jurisdictions

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