Depigmenting action of hydroquinone depends on disruption of fundamental cell processes.

The effect of the skin-depigmenting agent hydroquinone (HQ) on 2 melanotic and 3 nonmelanotic cell lines was studied. Significant differences in its effect on DNA and RNA synthesis were observed between cell lines. HQ caused inhibition of cellular metabolism in all cells tested, but the dose that caused 50% inhibition of tritiated thymidine incorporation was approximately 30 times lower for melanotic cells. Tritiated uridine incorporation was found to be 85 times more sensitive to HQ in the melanotic cells. These results suggest that HQ exerts its depigmenting effect by selective action on melanocyte metabolism rather than a specific effect on melanin synthesis. Further, the effects of UV irradiation on this system were investigated and found to be negligible, in spite of the stimulation of in vivo melanin synthesis by UV radiation.