• Subject headings describe the topic of a paper, similar to tags or hashtags.
• They are pre-defined, controlled vocabulary that standardizes and pulls together synonyms, alternate spellings, and different word endings.
• Subject headings are arranged in a hierarchy, from broader to more specific.
• Subject experts add these subject headings using the most specific and relevant heading available.
• Depending on how substantially this topic is covered in the paper, these are added to either the Major Subjects or Minor Subjects fields.

Many specific health science databases will contain a subject heading resource. This page looks at one database CINAHL, but the strategies outline can be adapted for other databases. 

Keywords are specific words chosen to represent a concept. Searching for them in the title and abstract fields will locate papers where the concept is highly relevant.  Keywords are also called textwords or natural language. 

Keywords are helpful when:

• An appropriate subject heading does not exist
• The term is very specific, jargon or a brand name etc.
• The concept is new to the literature
• The search term is a condition or therapy that is very rare
• The paper has not been indexed as it is either too recent, or not indexed in CINAHL

When using keywords or natural language we need to take into account:

• Spelling variations
• Synonyms
• Plural forms 

The Explode tool selects the selected heading as well as any narrower terms that are indented below it. This is a useful shortcut, for example, Explode Canada will find papers that are tagged with the heading of Canada as well as any that are tagged with the Provinces. If some of the terms are not relevant to your question, uncheck explode and select only the terms that match your question.

The Major Concept tool will only search for those articles where the topic is the main point of the paper. Where a subject heading has been designated as a major concept of the paper, it is listed under Major Subjects on the document's profile and identified by a MM in the search history.

• Major Concept can be useful when needing a few very relevant papers on a single topic
• Generally it is not a good idea to use this

Subheadings allow you to choose a specific aspect of your topic. For example, adding Trends will find papers about the changes over time that diapers have had or may have.

• Include All Subheadings is selected by default. In most cases, this is the best option.

In CINAHL on the EBSCO platform you will see MH used to indicate that a subject heading has been searched; a + sign to indicate the subject heading has been exploded; and MM is used to indicate that the subject heading has been limited to results where this is a focussed/major concept of the article. (MH "Wound Care") - subject heading search (MH "Wound Care+") - exploded subject heading search (MM "Wound Care+") - exploded and focusssed/major concept search.