Worth a closer look
Evidence key Strong Moderate Weak How we grade
Skin allergen Possible carcinogen Suspected genetic damage Chemical of concern Restricted in the EU
- What it can be used for
- Adds scent, breaks down hair bonds (in perms and straighteners), dyes hair, lightens and stops the product from going off (the functions the EU ingredient database, CosIng, lists for it; a product may use it for any of them)
- CAS number
- 123-31-9
Why it’s flagged
Classified as a skin sensitizer (may cause an allergic skin reaction).
- Skin Sens. 1 (H317). Source: EU CLP Regulation, Annex VI harmonized classification
EU hazard statement H317: may cause an allergic skin reaction.
Classified as a possible or suspected human carcinogen.
- EU classification Carc. 2. Source: EU CLP Regulation, Annex VI harmonized classification
IARC Group 2B means possibly carcinogenic to humans. EU Carc. 2 means suspected human carcinogen. These describe a hazard, not the risk at the amount in one product.
Classified as suspected of causing genetic defects.
- EU classification Muta. 2. Source: EU CLP Regulation, Annex VI harmonized classification
EU Muta. 2: suspected of causing genetic defects.
Listed as a chemical of concern by the Campaign for Safe Cosmetics.
- “Hydroquinone”. Source: Campaign for Safe Cosmetics
The Campaign for Safe Cosmetics is an advocacy group. Its profiles explain why it considers these ingredients a concern.
Allowed in EU cosmetics only with limits.
- Annex II entry 1339 bans only this form: “1,4-Dihydroxybenzene (Hydroquinone), with the exception of entry 14 in Annex III”. Source: EU Cosmetics Regulation, Annex II (prohibited)
- Annex III entry 14; products: Artificial nail systems; max 0.02% (after mixing for use); Professional use; required warning: – For professional use only; – Avoid skin contact; – Read directions for use carefully. Source: EU Cosmetics Regulation, Annex III (restricted)
Annex III (restricted substances) or Annex V (preservatives) of the EU Cosmetics Regulation sets maximum amounts, allowed product types or required warnings.
What the research says
We have no graded research on Hydroquinone by name yet. About ingredients flagged like this one:
- In a survey of 187 US pediatric personal-care products, preservatives (57.8% of products) were a more common source of contact allergens than fragrance (29.4%), even though the products were being screened specifically for hypoallergenic/fragrance-related marketing claims. Moderate evidence. Hamann 2015
Each finding shows its evidence grade. See every graded fact or how we grade.
What this page can’t tell you
These lists describe what a substance can do, its hazard. The risk from one product depends on how much is in it and how you use it, and the label doesn’t say how much.
Not being on a list doesn’t make an ingredient safe. It may never have been assessed.
Check your products
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Flagged the same way
Official lists checked September 2026. Spotted a mistake? Tell us.