Firstly, the relevance of titles was evaluated, secondly the relevance of abstracts from hits with relevant titles was evaluated and thirdly the relevance of full texts from hits with relevant abstracts was evaluated. A search was made based on the function 'related studies' for each relevant study in each database. The reference list of each relevant study was viewed and searched in Web of Science for citations. Finally each accessible relevant study was read carefully (5 hits). Exclusion criteria were studies on closed farming, mechanized farming, non-tropical conditions, and farming in industrialized countries or laboratory performance testing of personal protective equipment seeing that these criteria would not represent typical farming conditions in developing countries. Grey literature was searched in databases of the International Labor Organization, World Health Organization and Food and Agricultural Organization.