Why Does My Shower Drain Smell Like Sewage?

A shower with drain

YinYang / Getty Images

The pungent odor of sewage wafting out of the shower drain is enough to wrinkle most noses and encourage users to find a solution as soon as possible. After all, it's hard to feel clean, even right after bathing, if the place where you go to wash gives off the foul stink of waste and sewage. If your shower drain is giving off a terrible odor, this situation can be a result of several possible causes. The good news is that generally, a smelly shower is a relatively easy problem to resolve once you identify the cause.

There are several common causes for a sewage odor coming up from the shower drain, including a clog in the drain line, a dry or dirty P-trap, mold or biofilm build-up, and leaking drain lines in the walls, ceiling, or under the floor.

Drain Clogs

One of the most frequent problems with a shower that can result in foul odors emanating from the drain is a clog. Dirt, grime, oils, hair, and other debris can get trapped in the drain line and act as a barrier, preventing similar items from getting washed down the drain. The formation of a clog takes time, so you may not notice a smell when the clog first starts to form, but over the course of a few days or weeks, trapped hair, mineral deposits, and soap scum can start to give off offensive odors.

To help prevent clogs, it's recommended to invest in a drain strainer that can catch a lot of the hair and debris that would otherwise get washed into the drain. However, it's important to make sure that you regularly empty and clean the drain strainer. If hair, dirt, oils, and debris are left in the strainer, they will start to break down, causing the same foul smell as a drain clog.

Solution: Unclog and Clean the Shower Drain

If you suspect that the reason behind the foul stench in your shower drain is due to a clog, then there are several methods to try to unclog the drain. The first method is to physically pull out or dislodge the clog by feeding a plumber's drain snake into the shower drain. If you are trying to pull the clog out, make sure the drain snake has a hooked end to grab onto hair and debris, but if your goal is to break up the clog, then it's best to invest in a drain snake with an auger mechanism that can bite into and through the clog using rotational force.

Alternatively, you can pour boiling water into the drain to try to melt any oils that make up the clog in order to dislodge it. Chemical drain cleaners can accomplish the same results, though they can also damage the drain line. If you risk using chemical drain cleaners, make sure to read and follow the manufacturer's directions for the best results.

Dry or Dirty P-Trap

The P-trap for a shower drain is located under the shower. This piece of plumbing is a U-shaped section of pipe that dips below the rest of the shower drain line. The reason for this shape is to trap a small amount of water in the drain line in order to prevent gases from the sewer line from escaping up through the shower drain. Dirt, grime, hair, oils, and other debris can settle in this pipe, resulting in a foul scent rising up from the drain.

However, a dirty P-trap isn't the only problem that could result in a sewage smell from the shower drain. The P-trap may also be dry, indicating that there is a clog in the ventilation line. Plumbing vents pull air into the plumbing system to help move waste and wastewater through the pipes and out of the home. If the vent is broken, clogged, or otherwise obstructed, this can create a vacuum that pulls the water out of the P-trap, leaving it dry. When the P-trap is dry, the odors from the drain line are free to escape through the shower drain.

Solution: Clean and Sanitize the P-Trap

A dirty P-trap is relatively easy to clean and sanitize in order to get rid of musty odors. You can use chemical cleaners to remove any dirt and grime clinging to the inside of the P-trap, but if you are concerned about using harsh chemicals in your plumbing lines, then you may want to try an alternative solution. Pour about 0.5 cups of baking soda into the drain and follow it up with about 0.5 cups of distilled vinegar. Cover the drain with a stopper and allow the chemical reaction to take place within the drain. This should remove any odor-causing bacterial and clean out any grime or debris that is clinging to the inside of the drain line.

If the problem is a dry P-trap, it's likely a result of a broken, clogged, or obstructed vent line. This situation tends to be beyond most DIYers, so it's recommended to contact a professional plumber to help resolve the problem.

Biofilm Build-Up

Biofilm is a substance similar to mold, but distinctly different in that it is formed from a dynamic colony of bacteria and bacterial waste. It has the appearance of muck, grime, or slime, and can come in several different colors, though the most common colors are pink or orange. This slime can build up inside the shower drain, and can even spread into the actual shower, leading to musty, unpleasant scents.

Biofilm feels slimy and tends to have a glue-like texture that clings to surfaces. You can see biofilm outdoors on river rocks or birdbaths. Due to the wide range of biofilm types, it can be difficult to determine exactly what you are dealing with in your shower drain, but the important thing is that you get rid of the biofilm as soon as possible.

Solution: Scrub and Disinfect to Remove Biofilm

Biofilm can cause a foul odor that will make you think twice before stepping into the shower. To remove biofilm, you need to first use a brush or a similar tool to scrub the affected area and break up the film. Wipe away the layers of biofilm as well as you can with a simply brush, then follow it up by spraying the affected surface with an antimicrobial disinfectant.

It isn't as easy to clean biofilm out of a drain as it is to remove it from the shower tiles. Instead of a brush, consider using a paint roller cover. The long, narrow shape allows the paint roller cover to fit into the drain line. Coat the roller cover with an antimicrobial cleaning solution, then insert it into the drain and rotate the roller cover to break up the biofilm. Make sure to frequently pull out the roller cover, rinse it off in a bucket of hot, soapy water, then push it back into the drain until you can pull the roller out without any signs of lingering biofilm.

Leaking Pipes

A leaking drain line is a serious issue that can cause the smell of sewage to come up from the drain or even emanate through the walls and into the bathroom. The waste and wastewater from the shower needs to flow down and into the main drain to exit the home. If the drain line is leaking, then there is a high likelihood that the wastewater will seep out into the surrounding area, saturating the insulation and the inside of the walls and floors.

If this situation is left for too long without a resolution, the leaking wastewater won't just create foul odors, it will also damage the drywall, insulation, framing, and any other materials that it comes into contact with, so it's important to address this issue as soon as possible. After fixing the leak, the odor issue may persist until the affected insulation and infrastructure are replaced.

Solution: Repair Leaking Pipes

One of the most problematic root causes of bad odors in the bathroom is a broken or leaking drain pipe. Leaks typically occur around a joint or a connection, but finding the leak is incredibly difficult because your drain lines are generally buried inside the walls and floor. This means that you may need to open up the walls or floor of the bathroom in order to access the damaged portion of the drain line.

You will also have to address any issues with the surrounding insulation, drywall, tiling, and other infrastructure because the leaking wastewater can cause water damage, rot, and rampant mold growth. Due to the complexity of this job, it's recommended to hire a professional plumber to locate the leak, fix the plumbing line, and suggest the next course of action. The pipe repair and wall repair may be all you need to worry about, but if the water damage is extensive, you may need to renovate the entire bathroom to fully resolve the issue. Consult with a plumber or a water damage restoration expert.

When to Call a Professional

Sometimes the problem falls outside of your personal experience and skill, so it's important to be able to recognize your limitations and make the call to a professional plumber when necessary. For instance, if the sewage odor is a direct result of leaking drain pipes running behind the walls, through the ceiling, or under the floor, then it can be difficult for the average DIYer to find the source of the leak, open up the walls, repair the leak, and deal with any mitigating damage left over.

Similarly, a dry or dirty P-trap can be the result of a clogged vent line. These vent lines typically run up to the roof, so if you don't feel comfortable working on the roof or you aren't sure how to identify the vent line once you are up on the roof, then it's better to call in a professional. Experienced plumbers have the knowledge and training to quickly identify the source of the odor and come up with an effective solution to the problem.