Obagi-C Rx C-Clarifying Serum is a 4% hydroquinone plus vitamin C serum. This one-of-a-kind serum delivers hydroquinone and L-ascorbic acid, also known as vitamin C, to the deep layers of your skin. The hydroquinone works to lighten your skin by reducing melanosome activity. Melanosomes are a necessary part of how cells make melanin, the pigment that gives skin its color. If melanosome activity is reduced, so is the pigment, diminishing the appearance of dark spots. Suitable for normal to dry skin, this hydroquinone and vitamin C serum helps even out your skin tone and lightens unwanted hyperpigmentation.