The terms Dermatitis, Contact and Epoxy Resins are MeSH terms (indicated by the / symbol).
Note that both have the term exp in front of them.
This indicates they have been 'exploded', meaning all the lower terms in the MeSH tree are searched also. Dermatitis, Contact has the subcategories shown here.
If explode is not selected then these subcategories will not be included in the search, changing the results significantly. The decision to explode or not will depend on the requirements of the search.
Synonyms have been added in line 2. These are then combined with the preceding MeSH results using OR (line 3).
Truncation (*) has been used to include sensitivity or sensitivities.
Note the increase in final results from 5 to 40.