Rhododendrol

INCI: RHODODENDROL (ALSO KNOWN AS RHODODENOL / 4-(4-HYDROXYPHENYL)-2-BUTANOL / 4HPB)

CAS Number
501-96-2
Function
Skin lightening/depigmentation — tyrosinase inhibitor; originally developed and patented by Kanebo as a quasi-drug active in Japan
Safety Rating
POOR

Regulatory Status

🇪🇺 EU Status permitted
🇺🇸 US Status permitted
US Notes Not approved as an OTC drug active; could technically be used as a cosmetic ingredient, but post-recall stigma and liability risk make it commercially non-viable

For full compliance data across 55 jurisdictions, use the Substance Compliance tool.

Safety Data

Margin of Safety (MoS)
adequate
Dermal Absorption
high
Sensitization
moderate

Calculate MoS for your specific formulation with the MoS Calculator.

Expert Verdict

🚨 CRITICAL: Caused widespread chemical leukoderma (vitiligo-like depigmentation) in ~19,000+ consumers in Japan (2013); Kanebo recalled 54 products across Asia . Mechanism: rhododendrol is metabolized by tyrosinase into cytotoxic quinone metabolites that kill melanocytes. Do NOT formulate with this ingredient. Despite passing pre-market safety testing, post-market surveillance revealed serious irreversible harm .

⚠️
Concern Level: High

Frequently Asked Questions

Is Rhododendrol safe in cosmetics?

🚨 CRITICAL: Caused widespread chemical leukoderma (vitiligo-like depigmentation) in ~19,000+ consumers in Japan (2013); Kanebo recalled 54 products across Asia . Mechanism: rhododendrol is metabolized by tyrosinase into cytotoxic quinone metabolites that kill melanocytes. Do NOT formulate with this ingredient. Despite passing pre-market safety testing, post-market surveillance revealed serious irreversible harm . The EU classifies Rhododendrol as "permitted". Safety rating: POOR.

Is Rhododendrol allowed in the EU?

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

What does Rhododendrol do in cosmetics?

Rhododendrol functions as: Skin lightening/depigmentation — tyrosinase inhibitor; originally developed and patented by Kanebo as a quasi-drug active in Japan. It is classified as a cosmetic ingredient in our database. CAS number: 501-96-2.

What is the Margin of Safety for Rhododendrol?

adequate 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.

📱

Is Rhododendrol in Your Products?

Scan any product label with Piro — our free ingredient scanner. Point your camera at the ingredients list and get instant safety scores for every ingredient.

Try Piro Free →

Analyze Your Full Ingredient List

Paste any INCI list into the Decoder for instant safety analysis, or calculate the Margin of Safety for Rhododendrol in your formulation.