Air bubbles in a toilet bowl often signify an air ventilation issue in the toilet's drainage system. Additional signs of a ventilation problem include gurgling water and water levels that rise and fall.
Improper toilet ventilation often occurs in homes where toilets share drain lines with other appliances, such as washing machines, as this makes it easier for the lines to become clogged. If the plumbing issue is caught early, it can often be remedied by inserting a plumbing snake into the air vent pipe and turning it repeatedly until the blockage is removed and the vent begins to drain on its own.
