Cutaneous reactions to topical application of hydroquinone. Results of a 6-year investigation.

The investigation was designed to assess the safety of hydroquinone in cosmetic skin-lightening products, and to determine the optimal concentration for the purpose. The 840 volunteers who took part in the 6-year trial were drawn from various race groups with skins varying from very fair to very dark. They were subjected to open tests, "normal usage" tests, and standard 48-hour closed-patch tests. In all, over 7,000 test areas were examined. The results show that concentrations of hydroquinone of 3% and less produced negligible adverse effects, irrespective of the base or the colour of the user's skin. It is stressed that any confusion of hydroquinone with the hazardous monobenzyl ether of of hydroquinone (monobenzone, MBH) should be avoided.