A peptide selected from the group consisting of Hyp-Gly, Pro-Ala-Gly, Gly-Pro, Glu-Hyp-Gly, (Pro-Hyp-Gly)5, (Pro-Hyp-Gly)2, Pro-Hyp-Gly, Glu-Hyp, Ala-Hyp-Gly, Ser-Hyp-Gly and Phe-Hyp or a pharmaceutically acceptable salt thereof is useful as a whitening promoting agent or atopic dermatitis ameliorating agent.