PubMed

MeSH terms are used to catalog and index the article records in PubMed. They are arranged into tree structures and are updated every year to include new developments.

Although MeSH terms can be used in PubMed searches, they are found in their own database.  This database is similar to searching PubMed but keep in mind that:

• You are not searching article records, only subject headings.
• The search history in the MeSH database is distinct from the search history in PubMed.

To search MeSH, click on MeSH Database under Explore on near the bottom of the PubMed main page.

The National Library of Medicine has produced a short video on MeSH which can be viewed here: https://www.nlm.nih.gov/bsd/disted/video/index.html.

A record could merely contain the keywords you search for but not actually be about that subject.

Let's say that you wanted to research pulmonary cancer and cigarette smoking. Articles sometimes contain wording like this:

"Most research on lung cancer has examined connections with cigarette smoking. In this article we examined pulmonary cancer and chewing tobacco."

These sentences contain terms relevant to our search, but the article is about something entirely different.

MeSH terms are applied to articles after someone from the National Library of Medicine has actually read the article. By labeling an article with MeSH terms, they are telling you what the article is about.

It is also important to search the MeSH terms in order to capture relevant articles that do not use the keywords you have entered.

When searching MeSH, keep in mind:

• Each search result that you see is a different subject heading. These are not article records!
• Sometimes more than one subject heading will be relevant for your search. Review the results and open any that may be useful.

• MeSH pages for each term have certain standard features:
  • A brief definition of the term (sometimes called the scope note).
    
    • Any terms spelled with all capital letters are other MeSH terms.
       
  • Subject headings introduced after the early 1960s will display the Year Introduced.
    • MeSH is not retroactive: If a subject heading was introduced in 2017, citations from 2016 and earlier will not be indexed with that term.
       
  • Subheadings. These subheadings can be used to search for specific areas within the MeSH. You can search as many subheadings as you choose. Subheadings are sometimes referred to as "Qualifiers."
    
    • If you want to search using the Subheadings, click the boxes next to the desired terms. You can select multiple Subheadings at a time.
    • More information on subheadings is available here.
       
  • Entry Terms.  This section includes alternate and archaic terms, synonyms These terms are not subject headings, but you may consider using them as keywords in your search. Entry terms are sometimes called "cross-references."
    
    More information on Entry Terms is available here.
     

If you would like to perform a search for all citations with this subject heading, click Add to search builder in the top right area of the screen. The MeSH term will appear in the search builder box. Click Search PubMed to run the search using that term.

At the bottom of a MeSH page is the category tree. You can see where the term you are viewing is placed in the hierarchy and whether it might be more efficient to select a term above or below it in the tree. Terms closer to the top of the tree are broader while those at the bottom of the tree are more focused.

When you search using a MeSH term, PubMed will automatically search for the term you specific, but it will also search for the subcategories beneath that term as well. This is called "exploding" the subject heading.

If you do not want to search the subcategories, click the box next to "Do not include MeSH terms found below this term in the MeSH hierarchy" before you add the term to the builder.

A plus sign (+) is used to signify that there are more subcategories beneath a term that are not currently visible. These deeper categories can be viewed by clicking on the subject heading with the plus sign and then reviewing the category tree area there.

There are 2 downsides to searching with MeSH terms. Both of them are related to time.

1. MeSH is not retroactive: When a new subject heading is introduced, NLM staff do not go back through previous years to apply the heading to earlier citations. You can tell how old a MeSH term is by looking at the "Year introduced" field. MeSH terms that have recently been introduced are likely to have been applied to fewer article records than MeSH terms that have existed for many years.
2. It takes time to apply subject headings to citations: For this reason, newer citations do not yet have subject headings.

For these reasons it is important that you search using keywords and MeSH terms!