O'Donoghue, J L (September 2006). “Hydroquinone and its analogues in dermatology – a risk-benefit viewpoint”. Journal of Cosmetic Dermatology5 (3): 196–203. doi:10.1111/j.1473-2165.2006.00253.x. PMID17177740. "The potential toxicity of HQ (hydroquinone) is dependent on the route of exposure"
O'Donoghue, J L (September 2006). “Hydroquinone and its analogues in dermatology – a risk-benefit viewpoint”. Journal of Cosmetic Dermatology5 (3): 196–203. doi:10.1111/j.1473-2165.2006.00253.x. PMID17177740. "The potential toxicity of HQ (hydroquinone) is dependent on the route of exposure"