Why Does My Shower Drain Smell Like Rotten Eggs?

Shower drain smells like rotten eggs

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The bathroom is a high traffic area that gets used by friends, family, and other guests, so when the shower drain gives off a powerful rotten egg smell, it can give the impression that your home is dirty or in disrepair. If your shower drain smells like rotten eggs, it's important to find out what is causing the smell in order to resolve the issue, so you need to start by inspecting the drain for one of several common causes.

Typically, the rotten egg smell is created when bacteria grows in the drainage system and breaks down waste, forming the gas known as hydrogen sulfide. However, in some cases, the smell may be the result of contaminated water, so it's recommended to find the source of the rotten egg smell as soon as possible and take steps to fix the problem. Use this guide to learn why the shower drain smells like rotten eggs and how to go about solving this dilemma.

Clogged Drain

A clogged drain is a common problem that can occur due to the buildup of hair, soap, shampoo, conditioner, dirty, oil, and other debris. Fully clogged drains are easy to spot because the water becomes trapped in the tub or the bottom of the shower. However, if the drain is only partially clogged, it will still allow the water to drain out of the tub or shower. In these cases, the partial clog forms the perfect environment for bacteria to grow and spread.

The bacteria feed on soap scum, dirt, oil, hair, and skin that is washed into the drain. When the waste is broken down, it releases hydrogen sulfide gas, which seeps out of the drain and into the air of the bathroom, creating a rotten egg smell. To fix this issue, you need to unclog and clean the drain.

You can use a drain snake to pull out large hair clogs or break up oil and soap scum clogs in the shower drain. Another option is to pour baking soda into the drain, then add vinegar and cover the drain with a plug to allow the vinegar and baking soda reaction to clear the clogged drain. This method will also disinfect and deodorize the drainage pipe to get rid of the rotten egg smell.

Dry or Dirty P-Trap

The P-trap is a U-shaped or P-shaped part of the plumbing system immediately after the drain that is designed to hold water. The purpose behind keeping water trapped in this section of pipe is that the water acts as a barrier to prevent gas in the drainage system from seeping back up the drain and into your home.

If the P-trap is dry, then there isn't any water in the trap to prevent the gas from escaping through the drain. This can occur if a drain isn't used for a long period of time, or it may be due to a blocked or broken drainage vent. If the drain has not been used in a while, try running water into the drain to fill up the P-trap. This simple solution may solve your problem.

However, if there is a blocked or broken drainage vent, then this can create a vacuum in the drain line, which will empty the water in the P-trap. Vent stacks exit the home from the roof, so it's recommended to hire a plumber to clear or repair a vent stack.

Dirt and grime that has collected in the bottom of the P-trap may also be creating the rotten egg smell because the area would be prone to bacteria growth. Pour baking soda into the drain, then pour vinegar and cover the drain with a plug to force the baking soda and vinegar reaction down into the drain to disinfect and deodorize the P-trap.

Leaking Pipes

The rotten egg smell can also be a symptom of a much more severe issue. If the drain pipes behind the walls or under the floor are leaking, the waste in the drain will seep into the insulation and may even damage the drywall. A leak can also release pungent gasses from the drain line, but even if the gas remains trapped in the drain by a barrier of water, the area behind the wall or under the floor will soon become a breeding ground for bacteria and mold.

Mold and mildew growth tends to have a musty smell, while bacteria breaks down the waste escaping from the drain line and can create hydrogen sulfide gas, which smells like rotten eggs. Unseen leaks can cause a lot of damage, so as soon as you suspect that you have a leak it's recommended to repair the leak yourself, if possible, or contact a professional plumber to fix the leak and assess the bathroom.

Depending on the severity of the problem, after the leak has been fixed, you may still have to replace the insulation behind the walls or hire a professional for more extensive repairs to the tiles, drywall, or floor.

Biofilm Buildup

Mold is often the cause of musty or foul odors coming from the drains and appliances in the home, but when the drain smells like rotten eggs, mold is not to blame. Instead, this odor is created by a dynamic colony of bacteria and bacteria waste that looks like a glue-like slime or muck. This colony of bacteria is known as biofilm and it is usually pinkish or orange in color.

Biofilm forms when the bacteria have a damp area with ample access to resources, like soap scum, hair, oil, skin, dirt, and other debris. It is common around the lip of the drain, in the P-trap, and may also form if there is a partial clog in the drain, though biofilm tends to cling to most surfaces, including tiles, bathtubs, faucets, and shower heads.

The best way to get rid of biofilm is to clean the drain and any affected areas with a bathroom cleaning solution. You can also use a mixture of vinegar and baking soda for a quick DIY remedy that disinfects and deodorizes. Prevent biofilm from forming in the future by cleaning the bathroom at least once a week to keep the drains free from bacterial growth.

Contaminated Water

In rare cases, the water is the source of the rotten egg smell instead of the shower drain. If you suspect the water is the problem, take a sample and send it to a local lab for testing. Raw sewage may have seeped into the home water source or the water may have high sulphate levels, which will give off a powerful rotten egg stench. The test will be able to provide a clear picture of the composition of your water and may point to an explanation for the smell.

It's recommended to stop drinking the water until the test results come back. When you do get the water test results, make sure to speak to the lab for a detailed breakdown and ask about how to resolve the problem. If the only issue is a high sulfate level, you may be able to resolve the problem with an iron water filter.

Anode Rod Reaction

If the smell seems to only come from the hot water, then the issue may be caused by the water reacting with the anode rod. The water heater in your home may have an anode rod that is made from magnesium or aluminum. This rod is intended to protect the inside of the water heater from corrosion, but if your water has a moderate level of naturally occurring sulfate ions, the sulfate in the water can react with the anode rod and give off a potent rotten egg smell.

Magnesium anode rods tend to produce a stronger odor, so you may be able to fix the issue by replacing the magnesium rod with an aluminum rod. However, if the problem persists, then you may have to remove the anode rod entirely, though you would be eliminating the corrosion protection of the tank. Another option is to install an iron filter before the water enters the water heater to remove the excess sulfate ions and prevent the anode rod reaction entirely.