Think of MeSH (Medical Subject Headings) as the index to the book that is PubMed. It is the National Library of Medicine's controlled vocabulary (thesaurus).
When new material is added to the database, it is indexed by librarians at the NLM. The librarians read each article and add appropriate metadata (information about the article) that allows searchers to find it more easily. In addition to standard metadata (such as publication type, sex, species, and age group), the indexer also adds 10 to 15 Medical Subject Headings that describe what the article is about. These tags are selected from a standardized set of 28,000+ MeSH terms.
By using the exact wording of MeSH as part of your search, PubMed can include not just that specific term but also its synonyms, subheadings, and spelling variations. Search sensitivity is often greatly increased as a result.
NOTE The most recently added references may not yet be indexed with MeSH terms.
To see which MeSH terms have been assigned to an indexed article, click the MeSH terms heading in the Page Navigation section along the right side of the abstract. An example of one such section is shown below, but the wording will vary depending on the article.
Below is a list of the 20 MeSH terms assigned to one particular article. The terms marked with an asterisk (*) are designated as Major Topics of the article, and subheadings follow forward slashes. We can interpret this shorthand to mean that "methods of blood specimen collection" is a major topic of this article.
The easiest ways to access the MeSH Database are to
Using the search bar method, you can type any term into the search box and PubMed will attempt to translate it into a MeSH term. If it's unsure, or if you type a phrase with double quotation marks (as happens when you follow a link to the database), you will be presented with multiple options. For instance, searching the MeSH Database for eye (a very general concept) will pull up the results shown in the image below.
Note that each option provides scope notes (or definitions that describe how the term is used for indexing); these notes can be used to verify the term is the one that fits your search needs most closely. The capitalized words indicate related MeSH terms. The year introduced denotes the first year the term appeared in the index. (The term is searchable back to the earliest date shown.)
If you know you want to search for articles that discuss eye removal, you could either scroll down the list and click the appropriate term—which, in this case, you may need the scope notes to help you determine—or you could simply return to the search bar and type eye removal. The full resulting entry is shown below, and an explanation of the page's features can be found in the next section.