PURPOSE: An external preparation useful as a cosmetic or external quasi-drug, showing improved whitening effect, preventing effects on stain and freckle, safely usable without causing chapped skin, skin rash, etc., comprising a dehydroacetic acid as an active ingredient.

CONSTITUTION: An external preparation containing dehydroacetic acid which is used as an antiseptic for food, drug and cosmetic, exhibits improved inhibitory effects on melanin formation and is shown by the formula or a salt thereof as an active ingredient. The external preparation is used in the form of an ordinary cosmetic such as lotion, pack, milky lotion, cream, etc. and in the form of external quasi-drug such as ointment, lotion, liniment, emulsifying agent, etc. The external preparation contains 0.1W10wt% preferably 0.5W5wt% active ingredient in the case of cosmetic and 0.5W10wt%, preferably 0.5W5wt% quasi- drug.