MeSH (Medical Subject Headings) is the collection of indexing terms and controlled vocabulary applied to every single citation in PubMed. Searches of great specificity can be conducted in PubMed via the use of the MeSH hierarchy of over 26,000 subject headings. Some of the ways in which MeSH searches can be helpful follow:
Another way to discover MeSH terms for use in a search is to find an article in PubMed that is on topic, and then click on the "+" symbol next to the heading "Publication Types, MeSH Terms, Substances" which is located at the bottom of each citation in abstract view. Here you will see the MeSH terms that have been applied to an article and you can click on any that look useful to you and add them to your search. Note that article records are added to PubMed before they have been assigned MeSH terms (the MeSH terms are assigned later) so if it is a new article and you don't see MeSH terms it is because it has not had MeSH terms assigned to it yet (but fear not, they will be assigned to that article in the near future).
1) Got to the MeSH database by clicking on the MeSH Database hyperlink located under the More Resources heading on the PubMed homepage
2) Enter search terms into the search box and click the "Search" button
3) From the resultant list of possible MeSH terms, select the appropriate subject heading; for our example we will select "Breast Neoplasms" (Notes: a) there will not always be a MeSH term which is suitable for your topic b) there are often scope notes to help you determine if a particular subject heading is appropriate for your search)
4) Now mark the boxes next to any subheadings and other options you would like to use in your search (for a brief description of the components of a MeSH record, click here); Note that if you select no subheadings, all of them will be included by default. Once you have made your selections, click the "Add to search builder" button in the upper right corner. Now either search the MeSH database for more MeSH terms to add to search builder, add your own search terms to the search builder box, or leave it as it is. Click the "Search PubMed" button when you are ready to run your search in PubMed. Note that for our example, the subheading of "etiology" was selected and this is reflected in the text in the search builder box.
5) The search results from this search are shown below. To modify your search, try implementing some of the other tools in MeSH or using some of the tips found here for broadening or narrowing a PubMed search.