Why Does My Shower Drain Smell Like Rotten Eggs?

There’s nothing quite like a fresh-smelling home. But if your shower drain smells more like an expired egg than clean linens, that’s an issue that needs tackling. The truth is that there could be several reasons why a shower drain might smell like rotten eggs, from faulty plumbing to bacteria in the drain breaking down organic matter.

Here are the most common causes and what to do about them, in the order of ease of solving the problem.

First, a Word About P-Traps

The term “P-trap” will pop up frequently, so it’s worth discussing what this plumbing apparatus is and what it does. A P-trap, also called a U-trap or drain trap, is a P-shaped piece of pipe that runs from the shower or sink to the drain system. It may be made of metal or plastic, but this pipe’s job is to retain some water in the bottom of its P-shaped portion.

The purpose of storing water in this portion of the trap is to prevent sewer gasses from traveling back up the drain system and out of the shower or sink. Without a P-trap, nothing is stopping those gasses, which not only smell awful but could also be dangerous. This simple device solves that issue, and it’s required by building code.

Potential Problem #1: Dry P-Trap

When a P-trap runs dry, it’s no longer able to block sewer gasses from escaping the shower drainpipe. This is most common in guest bathrooms that aren’t used often, as without a fresh shower to refill the trap, the water in the trap will evaporate.

Solution: Run Water into the Drain

This one is easy to solve: Just turn on the shower. Running the shower for a few minutes will refill the trap, allowing it to prevent the sewer gasses from escaping. If a particular bathroom doesn’t get much use, it may be hard to remember to do this task periodically. So, you may want to consider setting a drain-filling reminder on an app or digital assistant. The frequency will depend on factors like the home’s humidity level, the location of the drain, the season, and how often the drain is used, but every two weeks or so should do the trick.

Potential Problem #2: Biofilm

Biofilm describes many types of bacteria consisting of microorganisms in which cells stick together, creating a slimy, mold-like film. Biofilm commonly occurs in areas that are consistently damp and where there is plenty of organic material for the bacteria to feed on. With the P-trap constantly filled with water and hair, skin cells, skin oils, and soap scum, among other debris, it’s no wonder why shower drains are prime locations for biofilm to develop. (A hot tub is another hot spot.) As the bacteria break down these materials, they emit an odor similar to rotten eggs.

Solution: Clean the Drain

The best way to beat biofilm and prevent it from stinking up the house is to clean the drain. A standard drain cleaner will do it, but one of the best home remedies is a combination of baking soda and vinegar. As the two react, they create a foam, with the baking soda particles helping to scour the biofilm from pipe. Flushing hot water down the drain afterward will help clear any remaining biofilm from the drain.

Potential Problem #3: Clogged Plumbing Vent

While a lack of use can cause the water in a P-trap to gradually evaporate, a clogged vent can suck it dry more quickly. Plumbing drain systems have open vent pipes on the end of the system, and these pipes typically extend up and out of the roof. These pipes allow fluids flushing down the system to flow without causing a vacuum.

If the vents clog, whether from debris, a bird’s nest, a bee’s nest, or a trapped rodent, a vacuum will form when someone runs fluids down the drain through the shower or toilet. That vacuum will start to pull the water from a P-trap nearby, lowering the water level and causing the gasses to eventually escape the drain. This is most common in taller homes where the fluid flushed has a longer way to travel. The trap will then allow sewer gasses by since the water level has dropped due to the vacuum.

Note: A shower plumbing clog, which is a blockage in the actual drain pipe, will usually present itself far sooner than the odor. However, if a blockage does go unnoticed for long enough, a smell could occur.

Solution: Clear the Vent

Unclogging the vent is the only way to truly fix this issue. This can be done with a snake from inside the home if there is access to a cleanout, or from the roof.

Potential Problem #4: Cracked Drain Pipes

Drain pipes can crack and break over time (specifically cast-iron pipes or PVC elbows and joints are more vulnerable). Should this occur, sewer gasses may be traveling up the pipe and escaping under the tub. This can result in the smell of rotten eggs in addition to leaks and damage to drywall or other surfaces in the home. And though it may smell like that odor is coming from the drain, it may actually be permeating from the floor underneath the tub.

Solution: Fix the Pipe

Find the cause of the leak and repair it. In the case of cast iron, this may require removing the entire pipe as corrosion is likely setting in. Repairing PVC pipes may be easier as all that’s involved is cutting the cracked section of the pipe and replacing it with a new length and some couplings. It’s also important to remove any wet insulation or damaged drywall to avoid mold growth.

Potential Problem #5: Sulfur Water

Sometimes, the smell that appears to be coming from the drain is actually because of the water running down it. Homes with well pumps often suffer from the problem of sulfur in the water underground. Sulfur smells like rotten eggs, making the bathroom or even the whole house smell.

If you’re having a hard time pinpointing whether or not this is the case, fill a glass with water and take it outside the home. Smell the cup outside and if it smells like eggs, you’ve found the cause.

Solution: Shock the Well System

In most cases, the easiest way to remove the rotten egg smell from your plumbing is to shock the well with a chlorine solution. This solution will kill the bacteria and cure the smell temporarily (1 to 2 months), though keep in mind that this is a job best performed by a licensed well contractor. A more permanent (albeit more expensive) option is to install a whole house well water filter to remove the sulfur smell as well as other contaminants from the water.

Potential Problem #6: Corroded Anode

Water heaters are prone to rust and corrosion. This is so common that manufacturers include a sacrificial rod—called an anode—inside the water heater that attracts particles of iron, limestone, and other minerals and sediment in the water. These particles then corrode the rod rather than the water heater tank. But, as the anode begins to fail, it can often cause the hot water to smell like sulfur or rotten eggs.

Solution: Replace the Anode or Water Heater

Replacing an anode can be very simple—if the tank has been maintained. All you need to do is unscrew the old anode and screw a new one in its place. However, if the water heater is old or hasn’t been properly maintained, it can be very difficult to remove the anode without damaging the water heater, too. Some folks would rather pay for a new water heater than try to remove the anode.

Get Back to a Fresh-Smelling Shower

One of these methods is bound to take your shower from eggy and stinky to fresh and clean. Though it may take trial and error in order to pinpoint the exact issue first, don’t give up as a solution to a shower drain free from odors may not be far off.