Environmentalists like to claim that unconventional gas developments are going to cause us all to die of cancer or asthma. It's fair to say that few of these claims are quite as bonkers as Friends of the Earth saying that the sand used in fracks is a dangerous carcinogen. However, while the other claims are not quite that absurd, they are not exactly grounded in good science.
A paper published today in a journal called Science of the Total Environment describes a review of the evidence for actual health impacts from unconventional gas and conclude there is little evidence of adverse health effects that you would want to describe as "firm". Of the 1000 articles the authors reviewed, fewer than 100 were considered worthy of further attention based on the quality of evidence presented. Only 7 could be considered "highly relevant". Health impacts were mostly "inferred rather than evidenced".
So you can understand why they would conclude:
Current scientific evidence for [unconventional natural gas development] that demonstrates associations between adverse health outcomes directly with environmental health hazards resulting from UNGD activities generally lacks methodological rigour.
But I think you could guess that anyway.