Why is hydroquinone banned in leave-on cosmetics in China despite its strong whitening effect?

Why is hydroquinone banned in leave-on cosmetics in China despite its strong whitening effect?
Hydroquinone remains the gold standard for skin lightening, with 2% concentration cited as the benchmark efficacy level in dermatology. However, its safety profile is heavily contested. Chinese cosmetic regulations permit hydroquinone only in artificial nail systems for professional use, explicitly banning it from leave-on products like creams and serums. The core concern is not acute toxicity but chronic low-dose exposure, which is exactly how cosmetics are used. Studies referenced in dermatological discussions link long-term use to exogenous ochronosis, with incidence rates reported as high as 42% in Black women and 15% in men, plus risks of permanent depigmentation resembling vitiligo. In China, hydroquinone is managed as a prescription pharmaceutical, allowed at 2-4% for short-term, medically supervised treatment of conditions like melasma. The regulatory divide between drug and cosmetic use reflects a risk-benefit assessment: controlled intermittent therapeutic use is acceptable, while unsupervised daily cosmetic application is not.