PURPOSE: To provide the skin external agent exhibiting a good percutaneous absorbing property, effectively inhibiting the coloration.decomposition of skin with light or heat, having an excellent melanogenesis-inhibiting action, and useful for preventing and also treating stains and ephelis.

CONSTITUTION: The melanogenesis-inhibiting external agent contains at least one selected from a group of iminodibenzyl compounds, dibenzocycloheptadiene compounds and ketotifen fumarate as an active ingredient in an amount of 0.00015-10wt.%, preferably 0.01-5wt.%. The addition of a whitening agent selected from a group of kojic acid, ascorbic acid, hydroquinone, liquiritin or their derivatives and a placenta extract gives a synergistic effect. The addition of an UV light absorbent (e.g. a dibenzoylmethane UV light absorbent or a plant extract having an absorption spectrum in a region ranging from the UV-B region to the UV-A region) and/or an antioxidant (e.g. a tocopherol compound) permits to effectively inhibit the coloration.decomposition of skin with light and heat.