sentence: Rhododendrol , 4 ‐ ( 4 ‐ hydroxyphenyl ) ‐ 2 ‐ butanol , Rhododenol ( Kanebo Cosmetics Inc ., Tokyo , Japan ) ( RD ) is a whitening agent , which was approved as a quasi ‐ drug by the Ministry of Health , Labor and Welfare of Japan in 2008 .