There are no poisons in natural gas that can be absorbed into the bloodstream when gas is touched or inhaled. The gas itself is nontoxic. There are situations, however, in which leaking or incompletely burning gas can create health hazards.
Natural gas can displace oxygen. When natural gas leaks into a confined space and the gas cannot dissipate, it can displace some of the oxygen in the space. This can create an oxygen-deficient atmosphere, which is an asphyxiation hazard. For this reason, you should wear self-contained breathing apparatus (SCBA) when responding to all natural gas emergencies.