Hydroquinone
AKA “Benzene-1, 4-benzenediol, Quinol, 4-Dihydroxybenzene, p-Hydroquinone, p-Hydroxyphenol, p-Benzenediol, p-Dihydroxybenzene”
Synthetic
Ingredient Facts
Hydroquinone
AKA: Benzene-1, 4-benzenediol, Quinol, 4-Dihydroxybenzene, P-Hydroquinone, P-Hydroxyphenol, P-Benzenediol, P-Dihydroxybenzene
Synthetic · Antioxidant · EWG: 4
Synthetic
Antioxidant
Skin Conditioner
Safety Concern
Synthetic
Not Clean
Helps maintain product stability and prevent color changes, keeping your formula fresh and effective over time.
Solubility 10 to 50 mg/mL at 68 °F (NTP, 1992)
Formula
C6H6O2
Mol. Weight
110.11
CAS #
123-31-9
Form
Powder
State
Hydroquinone appears as light colored crystals or solutions. May irritate the skin, eyes and mucous membranes. Mildly toxic by ingestion or skin absorption.
See origin →
Functions
Antioxidant
Fights free radicals — the unstable molecules from UV, pollution, and stress that break down collagen and cause premature aging.
Skin Conditioning
A catch-all term for ingredients that improve how skin looks and feels — softer, smoother, more supple. The workhorse behind most moisturizers.
Depigmenting
Shields from UV damage
Traditional Use
Discovered in the 1920s, hydroquinone was developed as a synthetic depigmenting agent to treat hyperpigmentation and melasma. Adopted in skincare in the 1950s-1960s as one of the first clinically proven skin-lightening ingredients.
Skin Types
●all-skin-types
Best For
Hyperpigmentation
Melanin-Rich Skin
Suitable
Pregnancy & Breastfeeding Safe
No
EWG
4
CIR
Safe w/Qualifications
Pregnancy
No
Restricted By
CIR Safety Findings
medical-approval
all-shades-safe
Mild Irritant
Concentration Guide
0.02%
0%0%
Reg. Limit
EU regulatory limit: 0.02%. - For professional use only - Avoid skin contact - Read directions for use carefully Source: EU Cosmetics Regulation (EC) 1223/2009, Annex III (Restricted Substances), Entry 14.
Regulatory Agencies
Final amended report on the safety assessment of oxyquinoline and oxyquinoline sulfate as used in cosmetics.
Andersen A
International journal of toxicology, 2006
Final amended report on the safety assessment of oxyquinoline and oxyquinoline sulfate as used in cosmetics.
Andersen A
International journal of toxicology, 2006
Addendum to the Final Report on the Safety Assessment of Hydroquinone
Cosmetic Ingredient Review (CIR) Expert Panel
International Journal of Toxicology
Amended Final Report on the Safety Assessment of t-Butyl Hydroquinone
Cosmetic Ingredient Review (CIR) Expert Panel
International Journal of Toxicology
Final Amended Report on the Safety of Oxyquinoline and Oxyquinoline Sulfate as used in Cosmetics
Cosmetic Ingredient Review (CIR) Expert Panel
International Journal of Toxicology
Final Amended Safety Assessment of Hydroquinone as Used in Cosmetics
Cosmetic Ingredient Review (CIR) Expert Panel
International Journal of Toxicology
Final Report on the Safety Assessment of Di-t-Butylhydroquinone
Cosmetic Ingredient Review (CIR) Expert Panel
International Journal of Toxicology
Final Report on the Safety Assessment of Hydroquinone and Pyrocatechol (Pyrocatechol has been Amended. IJT 16(S1) 11-58 1997.) (Hydroquinone has an Addendum. JACT 13(3) 167-230 1994.)
Cosmetic Ingredient Review (CIR) Expert Panel
International Journal of Toxicology
Final Report on the Safety Assessment of Oxyquinoline and Oxyquinoline Sulfate
Cosmetic Ingredient Review (CIR) Expert Panel
International Journal of Toxicology
Final Report on the Safety Assessment of t-Butyl Hydroquinone (Amended report JACT 10(1) 1-7 1991)
Cosmetic Ingredient Review (CIR) Expert Panel
International Journal of Toxicology
Final Report: Amended Safety Assessment of Hydroquinone as Used in Cosmetics
Cosmetic Ingredient Review (CIR) Expert Panel
International Journal of Toxicology
Di-t-Butylhydroquinone
European Commission
EU Cosmetic Ingredient Database (CosIng)
Hydroquinone
European Commission
EU Cosmetic Ingredient Database (CosIng)
Oxyquinoline
European Commission
EU Cosmetic Ingredient Database (CosIng)
Oxyquinoline Sulfate
European Commission
EU Cosmetic Ingredient Database (CosIng)
Ubiquinol
European Commission
EU Cosmetic Ingredient Database (CosIng)
Hydroquinone
Environmental Working Group (EWG)
EWG Skin Deep Cosmetics Database
Oxyquinoline
Environmental Working Group (EWG)
EWG Skin Deep Cosmetics Database
Oxyquinoline Sulfate
Environmental Working Group (EWG)
EWG Skin Deep Cosmetics Database
t-Butyl Hydroquinone
Environmental Working Group (EWG)
EWG Skin Deep Cosmetics Database
Ubiquinol
Environmental Working Group (EWG)
EWG Skin Deep Cosmetics Database
8-Hydroxyquinoline and its sulfate
Health Canada
Health Canada Cosmetic Ingredient Hotlist
Hydroquinone
Health Canada
Health Canada Cosmetic Ingredient Hotlist
An update on the safety of hydroquinone.
Kavya Shivaram, Katherine Edwards, Tasneem F Mohammad
Archives of dermatological research, 2024
An update on the safety of hydroquinone.
Kavya Shivaram, Katherine Edwards, Tasneem F Mohammad
Archives of dermatological research, 2024
An update on the safety of hydroquinone.
Kavya Shivaram, Katherine Edwards, Tasneem F Mohammad
Archives of dermatological research, 2024
Verified Feb 2026
Data: PubChem · CosIng · EWG · CIR