External application base or auxiliary agent and external application composition for human being or animal containing the same

A base or an auxiliary agent for external application for a human being or animal, comprising a polymer or copolymer of N-vinylacetamide having a structure containing 50 to 100 mole % of the repeating unit represented by the formula (I) and 0 to 50 mole % of at least one kind of the repeating units represented by the formula (II):

• ##STR24## wherein R.sup.1 represents H, CH.sub.3, C.sub.6 H.sub.5, or COOM, wherein M represents H or an alkali metal;
• R.sup.2 represents H, CH.sub.3, COOM;
• and X represents COOM;
• when R.sup.1 and X are COOM, the formula (II) also may have a cyclic acid anhydride structure.