OBJECTIVES: Perform a systematic review of the literature on effects of fracking (including other unconventional extraction techniques of oil or gas) on human health.

METHODS: We searched Pubmed and Scopus. Free terms used were: ("fracking" OR "hydraulic fracturing") OR ((unconventional OR flowback OR shale) AND (gas OR oil)) without language limits, but limited the search to publications during last the 20 years (search date November 06, 2018). Literature search in Scopus only included journals classified as Medicine, Biochemistry, Genetics and Molecular Biology, Psychology, Immunology and Microbiology, Nursing, or Health Professions. Initial selection of relevant articles, based on title and abstract, was done separately by 2 members of the research group and full-text versions were obtained for data extraction. The list of references of each study was analyzed manually to apply a snowball strategy. Due to heterogeneity in included references methodology, we did not rate quality of evidence with a standardized method.

RESULTS: Initial search retrieved 2420 references, of which 166 articles were included. Additionally, 124 relevant articles were identified after the “snowball” was applied. Out of 232 articles with geographical reference, 153 (75%) came from US; 21 (9%) from UK; 17 (7%) Canada, 5 Germany, 4 Australia, 3 Norway, one each from Albania, Argentina, China, Japan, Netherlands, Poland, South Africa, South Korea, Spain, and Switzerland. We included original research articles, literature reviews, letters to the editor, commentaries and regulatory agencies reports.

CONCLUSIONS: Current evidence is not enough to show causal association between adverse human health outcomes and fracking. There is, however, moderate evidence that associates air pollutants released during UET with respiratory health effects. Long-term health effects, such as birth defects, cancer, endocrine disruption and reproductive effects were seen as possible. While current scientific evidence leaves questions unanswered about health impacts, there is no evidence that support safety of fracking.