Many studies have linked illnesses to how many gas wells are nearby and how close they are to people. Studies have documented problems up to 10 kilometres from wells. Because they can be inhaled, swallowed, and also reach the skin, the potential for exposure to volatile chemicals is greater. Thus, air pollution has emerged as one of the primary public health concerns. Shale gas chemicals have also created record-breaking amounts of ground-level ozone that have been documented as travelling more than 300 km from its source, aggravating asthma, respiratory diseases, and irreparable lung damage.