Q&A / 

Shower Drain Odor

DEAR TIM: We have a horrible odor coming from the shower drain in our acrylic shower. Five different plumbers have not been able to solve the problem. The first and fourth plumbers said nothing could be done, the second and third plumbers thought the problem was caused by a rocking toilet so they replaced the toilet's wax ring. The fifth plumber said he thought the plumbing drain lines were installed improperly and that the odor was caused each time the toilet flushed. The problem is, the odor just started and all was fine several months ago. I have poured every imaginable cleaning solution into the shower drain and the odor persists. What could be the problem? Shari W., Rancho Palos Verdes, CA

DEAR SHARI: You might be eligible for a place in the record books for having called in that many plumbers for one problem. It is amazing that you have not made any progress on solving the problem. That tells me the source of the odor might not be plumbing related. But to determine this, I am afraid you might have to perform a little exploratory surgery on a wall that is adjacent to the shower.

Odors coming from drains are a common problem in many homes. Some people only have the problem when they run water in a sink or a bathtub. The source of the odor in almost all of these instances is a buildup of biofilm on the sides of the pipes that connect the sink or fixture to the actual P-shaped trap under the fixture. This vertical tailpiece pipe can accumulate a seething bacteria-filled organic layer of slime over time. When water rushes past the slime, it can dislodge some of the molecules into the air and they waft up out of the sink and into your nose.

Biofilm on the drainpipe leaving a shower or any fixture can be a source of odors. Look at the horrible black goo inside the drain! PHOTO BY: Tim Carter

Biofilm on the drainpipe leaving a shower or any fixture can be a source of odors. Look at the horrible black goo inside the drain! PHOTO BY: Tim Carter

To eliminate biofilm as the source of the odor, take the chrome or brass strainer cover off the shower drain so you can see into the drain pipe. Use soap and water and a larger-diameter bottle brush to thoroughly clean the underside of the strainer, the bowl-shaped drain assembly under the strainer as well as the sides of the vertical drain pipe that extends downward into the p-trap. Rinse thoroughly with clean water until the entire drain is perfectly clean. If the odor still persists, it is time to move on.

Check for mold in the shower and areas near the shower. Active mold growth produces odor. That musty odor you smell when around mold is actually a puff of gas that ejects the mold spore from the mold organism. Imagine if hundreds, thousands or tens of thousands of small mold spores are being ejected each day in your shower. This could easily produce enough gas for you to smell. Remember, this mold could be behind the shower tile or walls and hard to discover. A recent leak that is still invisible could be the source of water that is fueling the mold growth.

A dead animal that somehow found its way into the wall space next to the shower or under the shower assembly could be the source of the odor. This is a remote possibility and the stench of a decaying animal is very distinctive and quite unlike the odor produced by sewer gas or biofilm from a drain assembly.

If this shower shares a common wall with a closet or some other wall surface that can be sacrificed, it is time to cut into the wall(s) to see behind and under the acrylic shower assembly. The first holes can be down low towards the floor so that you can see under the shower pan. Purchase an inexpensive makeup compact mirror and attach it to a stick so you can see around any corners or obstructions under the shower pan. Use a flashlight with the mirror to look up the wall cavities as much as possible to see signs of mold growth.

Odors from drains are voices telling you something is wrong. Think of them as low-powered smoke detectors. This is especially true if the source of the odor is some form of mold. It is not uncommon for a water leak to remain invisible for weeks or months and cause mold to bloom in a hidden location.

Add to this the power of the average human's sense of smell. You would be shocked at how few odor molecules it takes to trigger a response. Natural gas is a great example of this. In its pure state, natural gas is odorless. Gas companies add mercaptan chemicals to the gas so we can smell it if there is a dangerous gas leak. Believe it or not, you can easily smell mercaptans at a concentration level of one-half one part mercaptan to 1,000,000 parts of air!

Investigate the source of all odors. Enlist the help of friends if possible, especially those who might have a better sense of smell. Small holes drilled into walls can be very helpful to help track down the source of an odor. Insert a small clear plastic tube into the hole and determine if the odor is stronger or weaker in that particular location.

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25 Responses to Shower Drain Odor

  1. I am getting a musty order in my shower. The odor goes away once I run the shower, but returns in the morning. The contractor said it is coming from he drain. I cannot remover the strainer to pour in soap and water as it is sealed. I used washing soda and hot water. It helped but the smell does return. I appreciate any suggestions. Thank you.

    • Marie,

      You need my Stain Solver. But to use it correctly, you must pry up the strainer. You mix up some Stain Solver solution, pour it in the drain, then use a bottle brush on the sides of the pipe. Then RINSE with the rest of the Stain Solver solution.

  2. Hi, I just had my shower re-done, all new walls, tile, floor pan, everything. I have not used the shower yet as we are still waiting for the door, however, in these last couple of days I have a definate sewer smell coming from the drain. This smell has NEVER been present before. I have an appointment with the contractor and would like to go in armed with just a bit of knowledge. I have flushed the drain with some water, but it still smells. Any thoughts would be appeareaciated, I have read these threads, there should be no "biofilm"everything is new! thanks!!

    • Hi, I know this comment is quite old, but we are having the 'exact' same issue. New walls, tile, shower drain, shower pan, waiting for shower glass. Sewage odor seems to be coming up the drain every day, mostly in the afternoon. Did you get a solution to your issue?

      I have inspected under the house an do not see any leakage. Any inputs are appreciated. Thanks.

  3. I just rent a house ,the drains looks grows green black ,white more black. looks like is eating the pipes . Locks very bad ... Can it be clean worry for my mom she is 75 . Just got the keys of the house. Thanks.

  4. My parents bought a home a few months ago.and all.of a sudden there shower drain smells like cigarette smoke. Neither of them smoke and there house has never been smoked in. The rest of the house smells fine. what can we do or what is causing the smell.
    please let us know so we can fix the problem. Now you can smell it as you walk in there room

  5. I just recently unclogged my shower drain by using a hair removal liquid. This is when I started noticing the sewer smell. Is this type of liquid strong enough to burn through a metal P-trap.

  6. I live in a ground floor flat where a bath has been replaced with a wetroom shower. There has been an awful smell coming from the bathroom and stinking out the hallway so we removed the drainer from the floor to clean it and realised it goes straight down 2ft to the sewer, should the shower be hooked up like this and can sewer gases be harmful as the smell isn't going away? Thanks

    • Amber, a plumbing trap is a curved pipe that holds water in it to prevent gases from coming up from the sewer. You can easily see one under your kitchen and bathroom sinks. Wikipedia has some pictures: http://en.wikipedia.org/wiki/Trap_%28plumbing%29

      If you can see water FLOWING, that doesn't sound right. But I suspect you have a pipe that's 2 feet and goes to a trap and then connected to the sewer after the trap.

      Use a flashlight and look down your shower pipe. Is there gross slime growing on the sides of the pipe? If so, that's probably where your smell is coming from. Get a long handled brush and scrub that slime off, then pour some OXYGEN bleach down (making sure it runs down the sides of the pipe) and let it sit overnight. You might have to repeat this periodically.

  7. Had the same smell after cleaning drain. Most people overlook this, but a plumber helped me: It could be from the over flow valve which doesn't get treated from pouring down drain.

    Solve by filling/over filling bathtub and let soap/cleaner+ water pour through overflow. Voila!

  8. I have an musty odor coming from all my drains & toilets in my 1-/12 story house. This has been going on for 6 months now.
    I have tried bleach & peroxide and it works temporarily but the smell comes back when the water hits the drain. We've had the water tested and the smell it not coming from the water, hot or cold. I have called a plumber and he suggested replacing the hot water anode rod, but the water smell is fine.
    Any suggestions? Thanks.

  9. Hi, guys, great article. I can't figure out my issue. The sewer smell is coming up through shower trap in the ensuite but when I pour a bucket of water down it, it flows straight through and none is trapped. There is no leak anywhere and the laundry trough drains have water in their traps...the same smell has been in the laundry which is on the other side of the wall to the ensuite. So, I want to ask the question, if one of the traps is dry, will that cause the water in a nearby trap to flow straight through? If not, what else can I check, please? Additionally, we used the ensuite spa bath for the first time in a few years last week but I am thinking that's a coincidence. Cheers

  10. I have a walk-in shower in a new structure I've lived in for three years. I clean the walk-in religiously, but it just smells and there is mold(sometimes black, sometimes pinkish) growing up top on the untitled, painted area.

  11. I get an odor several hours aprox. 8 to 12 after water goes down drain, it is in the air and lasts several days.Drains don't really smell.Have had several people check house septic, roots etc. Could this be a leaking drain pipe? I'm now getting some signs of mold,not black.i go for several days without using drain.When I use it again, the same thing happens. I'm hope it is the pipe leak not the vent or drain under shower in basement.Is it possible to have drain leak for three years?I hate to open walls if this not possible. Thanks for your opinion!

  12. I have a very strong ammonia smell coming from the shower. We removed our tubs and replaced with walk in showers a couple of years ago. The smell is terrible. I think it's making me feel sick. It almost smells like cat urine or perm for the hair. What can I do? And is this dangerous to my health? Thank you

  13. OMG! I had a moldy smell coming out of my shower drain and could not get rid of it. Thank you so much! I popped up the strainer (easy) and the smell nearly knocked me over. The bottom of the strainer was loaded with black mold. Then I looked around the top of the pipe where the drain sits and there is a rim where water sits more black smelly mold. Then looked down the pipe and the whole pipe on the insides was black. I thought they were supposed to be white. So I took some bleach and poured it directly on the drain and in the drain. Guess what. I had a white pipe again. I cannot believe that this black mold gunk sits on the inside of the pipe. Gross. So does this mean the whole pipe is like this? Super gross. My house is only ten years old. I scrubbed the strainer, drain and inside of the pipe and now it is virtually white and strainer silver again. Can't wait to see if the problem goes away because all I can smell now is bleach. Why does the gunk build up on the sides of the pipe when water is running down it daily? Doesn't make much sense to me. Anyway, I guess it is something that I will have to keep an eye on. It is not happening in the bathtub drains, just the shower drain. Thank you Thank you!!! I didn't even know that strainer could pop right up.

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