Introduction to MeSH
The following is an introduction to the Medical Subject Headings (MeSH) thesaurus, including its use and structure, as well as recent updates and availability of data. For simplest access to MeSH we suggest the MeSH Browser, an interactive Web application for searching and browsing MeSH data.
- Structure of MeSH
- Data Elements in MeSH records
- Use of MeSH
- Changes to MeSH Terminology
MeSH Vocabulary Changes: In biomedicine and related areas, new concepts are constantly emerging, old concepts are in a state of flux and terminology and usage are modified accordingly. To accommodate these changes, descriptors must be added to, changed or deleted from MeSH with adjustments in the related hierarchies, the Tree Structures.
There are many factors that must be considered in deciding whether to add a MeSH descriptor. An interest in one species of a given genus, may lead to interest in some other species or even all of that genus. Yet, if there is little published about the other species, there is little purpose or advantage in creating a myriad of new descriptors in a vocabulary designed to describe the subject content of published literature.
Before new descriptors are introduced, there is careful consideration of how the concept is currently indexed or cataloged. If the existing descriptors and qualifiers (subheadings) precisely characterize or identify the literature on the subject, there may not be a need for a new descriptor. Both too much change or too little change are to be avoided as MeSH is kept current with changes in biomedical knowledge. In selecting the expressions to be used for a new MeSH descriptor, it is the usual practice to adopt the expression most commonly used by the authors writing in the English language.
Lists are provided of: (a) new descriptors which have been introduced with the latest MeSH version; (b) descriptors which have been deleted, with the subject descriptors that have replaced them; and (c) descriptors previously listed with a different name, following this introduction.
- MeSH Descriptors and MeSH Qualifiers are released annually to coincide with the calendar year. Typically the next year's data is released in late November of the prior year to allow time for MeSH users to update their systems. A preview of changes MeSH data can be found on our What's New page.
- Supplemental Records (SCRs) are updated continually and released on a daily basis, Monday through Friday throughout the year. A yearly cycle of SCR updates is also done in order to synchronize SCRs with additions, subtractions, and changes made to Descriptor and Qualifiers.
- Year End Processing (YEP) is done every year on PubMed citations in order to update existing citations with new terminology. The YEP process is synchronized with the release of MeSH so the searches using the latest MeSH vocabulary will retrieve the appropriate citations.
- Availability of MeSH Data
MeSH Update Information: XML MeSH and ASCII MeSH are updated daily Monday through Friday. Updates are available at 7:00 AM. Generally only Supplementary Concept Records (SCRs) are regularly modified but if changes in Descriptors and Qualifiers are made, these are also included in the daily updates.
Last Reviewed: December 27, 2021