Soy contains at least two compounds that inhibit pigment formation.
The proteins, soybean trypsin inhibitor and Bowman Birk Inhibitor, interrupt the regulation of protease activator receptor-2. The PAR-2 pathway is known to regulate skin pigmentation. Topical soy compounds have been tried on people from various ethnic backgrounds. It doesn't cause changes in normal pigmentation, but it does prevent hyperpigmentation, it has been found. Daily topical applications for four to 28 weeks have been studied in people with hyperpigmentation disorders such as lentigenes, melasma and post-inflammatory hyperpigmentation.