PROBLEM TO BE SOLVED: To provide a low-cost skin external preparation that is easy to handle by a user.SOLUTION: A skin external preparation according to the present invention is a foamable skin external preparation comprising at least solid acidic substance, and solid carbon dioxide generating substance that reacts with the acidic substance to generate carbon dioxide. The skin external preparation further comprises at least one polysaccharide or a derivative thereof. The skin external preparation is mixed with hydrous substance at the time of use.COPYRIGHT: (C)2016,JPO&INPIT