A great deal of information concerning natural substances and their therapeutic effects has been gathered by the Natura Foundation over the past years.  This information is publicly available via this database.  You can find monographs that discuss the working, indications, contra-indications, side-effects and interactions of many commonly used nutrients and herbal extracts.  In addition, the searches are performed in files whose content is available without cost in PDF format.  The database is continuously updated and expanded.
If you are searching for an indication, you will see a list of possibly relevant indications after you enter your search term.  A search on the word “skin,” for example, will produce links to articles concerning acne, eczema, psoriasis and allergic reactions.  A click on one of these indications will take you to a list of supplements and herbal extracts which can be used for treatment.  You do not need to enter the entire search term; often the first few letters are sufficient.