Skin pigmentation disorders are common, and although they often do not affect consumers physically, many do psychologically.1 Since the discovery in the late 1930s of the depigmenting effects of monobenzyl ether of hydroquinone, a notable number of phenolic compounds have been evaluated as inhibitors of melanin synthesis.2 The most commonly used chemical whitening agents are hydroquinone, arbutin, kojic acid and ascorbic acid, and while most skin whitening agents are deemed effective, hydroquinone is still considered by dermatologists to be one of the most effective.
However, side effects such as burning, itching, crusting, swelling, skin discoloration and ochronosis—a persistent blue-black pigmentation—occur from some depigmenting agents, thus novel and effective solutions are sought. In recent years, new agents, especially from plants, have been discovered (see Potential Whitening Agents sidebar)and extracted to test for their depigmenting effects in vitro and in vivo. This article reviews these most recent skin whitening agents of interest, whose efficacy, mechanism and safety have been tested.3
Pro-Lys-Glu-Lys (PKEK) has been shown to reduce UVB-induced skin pigmentation in vitro and in vivo. In vitro, it was found to significantly reduce the UVB-induced mRNA expression of interleukin (IL)-6, IL-8, TNF-α, proopiomelanocorticotropin (POMC) and tyrosinase. This was demonstrated in a randomized, double-blinded and vehicle-controlled study on ten healthy volunteers. All volunteers were treated once daily for four consecutive weeks with the two test products on their buttock skin.
After four weeks, 30 min post-application of the creams, subjects were irradiated with a 1.4 minimum erythema dose (MED) of broadband UVB. Twenty-four hours after irradiation, 4-mm punch biopsies were taken from: the sham-irradiated control area (untreated), a UVB-irradiated skin area (untreated + UVB), a skin area pretreated with the vehicle formulation prior to irradiation (vehicle + UVB), and a skin area pretreated with the formulation containing PKEK prior to irradiation (PKEK + UVB).