MeSH是一部动态词表，为了保持与科学发展同步，每年都有相当数量的词汇增删变动。除去这些常规性变动之外，1991年、1992年、1995年及1996年又相继作了一些侧重于功能与结构方面的变动。1991年，M：SH做了一次重大改革：将其一直推崇、延用多年，但经实践证明确有不尽合理之处 MeSH is a dynamic vocabulary, in order to keep pace with the development of science, each year a considerable number of vocabulary additions and deletions changes. In addition to these regular changes, a number of functional and structural changes have been made in succession in 1991, 1992, 1995 and 1996. In 1991, M: SH made a major reform: it has been respected, extended for many years, but it has been proved to be not entirely reasonable