Objects of the present invention are to provide an oxidative stress inhibitor which is capable of suppressing the expression of a cytotoxic protein and the activation of a gene transcriptional regulatory factor taking part such expression of a cytotoxic protein and exhibits good feeling upon use and safety; to provide a method for preventing, retarding, alleviating or treating a skin change due to aging or an undesirable aesthetic skin change, both caused or promoted by an oxidative stress; and to provide a cosmetic composition or dermatologic preparation for external use comprising the oxidative stress inhibitor as an effective ingredient, and for those purposes are employed an oxidative stress inhibiting agent which comprises, as an effective ingredient, at least one selected from cysteine or cystine derivatives and the salts thereof.