To provide an inhibitor of melanin decomposition, which inhibits decomposition of melanin in keratinocytes to accelerate accumulation of melanin in skin and hair. An inhibitor of melanin decomposition in keratinocytes, comprising at least one selected from the group consisting of a plant extract containing berberine or a salt thereof, berberine or a salt thereof, proguanil or a salt thereof and phenformin or a salt thereof, as an active ingredient.
