| Cause | Description | |-------|-------------| | Excess toilet paper | Most common; paper forms a dense plug in the trap. | | Non-flushable items | Wipes, cotton buds, sanitary products, dental floss. | | Hard objects | Small toys, soap, or bottle caps. | | Mineral buildup | Over time, limescale narrows the pipe diameter. | | Sewer line issue | Rare; affects multiple drains, not just the toilet. |