Autoxidation of hydroquinone in ointments used for depigmentation may reduce its effectiveness. In this study low concentrations (2%, 3%, 5%) of stabilized hydroquinone were used for depigmenting "old age spots" on the hands of 94 white men. Also treated were 43 Negro men with normal skin. Higher concentrations of hydroquinone may produce sensitization. Lower concentrations are less likely to. Although the depigmentation produced by topical hydroquinone is limited, it is, in our experience, the best available depigmenting agent.
Spencer MC. Topical Use of Hydroquinone for Depigmentation. JAMA. 1965;194(9):962-964. doi:10.1001/jama.1965.03090220018004