May 4, 2026

You’ve cleaned the bathroom from top to bottom. The toilet is scrubbed, the floor is mopped, and you’ve even wiped down the tiles. And yet that smell is still there that low, unpleasant sewage smell that hits you every time you walk in. It’s one of those problems that feels personal, even though it almost always has a straightforward explanation. A sewage smell in bathroom spaces is more common than most people realise, and the cause is rarely as serious as it feels in the moment. But it does need to be tracked down and sorted, because it doesn’t go away on its own and in some cases, it can point to something that genuinely does need professional attention. In this guide, we’ll go through the most common reasons a bathroom smells like sewage, what you can check yourself, what the fixes look like, and when it’s time to pick up the phone. What Causes a Sewage Smell in the Bathroom? The sewage smell in bathroom situations usually comes down to one of a small number of causes. The smell itself that distinctive rotten egg or drain-like odour is caused by hydrogen sulphide gas and other gases that form as waste breaks down in the drainage system. Under normal circumstances, your plumbing is designed to keep those gases contained and directed away from your living space. When the smell gets through, something in that system has stopped working as it should. Here are the most common culprits. 1. Dried Out or Empty P-Trap This is the most frequent cause of a sewage smell in bathroom, and fortunately, it’s also the easiest to fix. Every drain in your bathroom the sink, bath, shower, and floor drain has a P-trap underneath it. This is the curved section of pipe that holds a small amount of water permanently. That water acts as a seal, blocking sewer gases from travelling back up through the drain and into the room. When a drain isn’t used for a while, that water can evaporate. No water means no seal, and the gases come straight through. This is particularly common with a guest bathroom that doesn’t get used often, a floor drain that’s never had water poured into it, or a bath that’s been sitting unused for a few weeks. The fix: Run water into every drain in the bathroom for about 30 seconds. For floor drains, pour a full bucket of water in. If the smell goes away within a few minutes, a dried P-trap was the issue. Job done. 2. Blocked or Slow-Draining Pipes A partial blockage in your bathroom drain doesn’t always cause the drain to stop working entirely. Sometimes it just slows things down and as waste and water sit in or move slowly through the pipe, they create the perfect conditions for unpleasant odours to build up. Hair, soap scum, and toothpaste are the most common culprits in bathroom drains. They accumulate gradually, coating the inside of the pipe and creating a layer of decomposing material that smells. You might notice the drain is slightly slower than usual, or you might just notice the smell particularly after a shower or using the sink. The fix: Start with a drain cleaner designed for bathroom use, or try a mixture of bicarbonate of soda followed by white vinegar and hot water. If the drain is still slow afterwards, a professional drain jet clean will clear the build-up properly and remove the source of the smell entirely. 3. A Leaking or Damaged Toilet Seal The toilet connects to the drainpipe at the floor through a wax or rubber seal sometimes called a toilet pan connector. Over time, this seal can degrade, crack, or work loose, particularly in older bathrooms or if the toilet has ever shifted slightly on its base. When the seal fails, sewer gases can escape into the room rather than being directed down into the drain. You might notice the bathroom sewage smell is strongest near the base of the toilet, or that it comes and goes without obvious pattern. The fix: Check if the toilet rocks or moves at all when you sit on it movement suggests the seal may have failed. This is a job for a plumber or drainage professional. The toilet needs to be removed, the old seal replaced, and the toilet re-fitted and secured correctly. 4. Blocked or Poorly Ventilated Soil Pipe Your soil pipe is the main vertical pipe that carries waste from your toilet and other fixtures down to the sewer or drain. It also has a vent typically extending through the roof that allows sewer gases to escape upward and out of the property rather than back into the bathroom. If this vent becomes blocked by a bird nest, leaves, or debris gases have nowhere to go except back into the house. You might notice a gurgling sound from the toilet or drains when water goes down, along with a persistent sewage smell in bathroom that doesn’t respond to cleaning. The fix: This requires a professional inspection. A drainage engineer can check the soil pipe and vent, clear any blockage, and confirm the system is venting correctly. It’s not a DIY job working near roof-level vents and soil pipes needs the right equipment and experience. 5. Cracked or Damaged Drainage Pipes Less common, but worth knowing about: if a drain pipe within or beneath your bathroom has cracked, gases can escape through the crack rather than being contained within the pipe. You might also get a slow seepage of wastewater into the subfloor or wall cavity, which creates its own persistent damp smell that’s easy to confuse with a sewage odour. This is more likely in older properties, particularly those with clay or cast iron drain runs, or in bathrooms where groundworks or building work has taken place nearby. The fix: A CCTV drain survey is the most reliable way to identify a cracked or damaged pipe. A camera is fed through the drain