What Causes a Bathroom to Smell Like Sewage?

The smell of sewage in a bathroom from a leaking sewage system can also carry gases other than just methane. The combination of gases, such as carbon monoxide, hydrogen sulfide and methane, can cause serious respiratory issues or even death if left unchecked. Clogged pipes are the most common cause of leaking gases and should be checked by a plumber or sewage expert immediately.