Photo: Andrey_Popov (Shutterstock)
Homes have a habit of harboring all sorts of nasty odors—cat litter, microwaved salmon, fly traps made from apple cider vinegar—that are blessedly easy to mitigate. Sometimes, though, you come across unpleasant smells that are harder to find and deodorize. Here are some common culprits, along with methods of attack.
There’s hidden mold
Maybe you’ve noticed a “musty” or “wet cardboard” smell in your home. Or perhaps you’ve referred to it as “old home smell.” Either way, one of the most common causes of lingering, musty smells, especially in older homes, is hidden mold, usually in the walls.
As you probably know, some types of mold can be toxic. According to the Environmental Protection Agency (EPA), most household mold problems under 10 square feet are safe enough to clean on your own and don’t need a professional, but to be safe, you should read up on the different types of mold at the EPA’s website here.
Then, the first real order of business? Figure out where that mold might be hiding. Here are some common culprits:
Leaky plumbingGutter issuesPoor ventilation in kitchen and bathroomsWindow frames where condensation builds up
For small, non-toxic mold problems, like the mold that accumulates on windowsills and frames, simply clean the mold with a soap and water solution, as instructed in the video. Vinegar or diluted bleach are also useful. Add it to water, then spray directly on the mold and clean up. For larger mold problems, you should call a professional.
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Prevention is key with mold, and the University of Missouri Extension offers some easy tips for keeping that nasty stuff at bay:
Keep closets, dresser drawers, basements — any place where mildew is likely to grow — as clean as possible. Soil on dirty articles can supply enough food for mildew to start growing when moisture and temperature are right. Greasy films, such as those that form on kitchen walls, also contain many nutrients for mildew-causing molds.
Spread a layer of moisture-barrier material over the soil in crawl spaces under houses. You can use heavy roofing paper or polyethylene plastic film. Good ventilation is important. If possible, do not enclose the crawl space. In extreme cases, a fan or blower may be needed to move the humid air from under the building.
In rooms that are not air-conditioned — especially the basement — mechanical dehumidifiers are useful. A humidistat can be attached to the unit to control the humidity. Mechanical dehumidifiers, however, can add heat to a room.
Take extra care in laundry rooms, kitchens, bathrooms, and basements, where moisture and humidity run amok.
Your carpet and walls have absorbed years of stink
Carpets and paint can absorb bad smells over time: smoke, pet urine, spilled milk. I always splash a fresh coat of paint on the walls when I move, and it typically gets rid of most lingering smells. If you’re renting, you might not be able to paint without getting your deposit back, so always check with your landlord first. At the very least, deep clean the walls, ceilings, and baseboards to get rid of as much of the stink as possible. Home Guides offers a couple of different solutions for getting rid of stubborn smells:
The White Vinegar Solution: …Start by adding warmed vinegar to a spray bottle for tough stains. Dilute using a one-to-one ratio with warm water for less noticeable stains. Apply the warmed vinegar or mixture directly to the walls. Because tar and nicotine develop a sticky and hardened surface, the warmth of the vinegar helps to soften these substances. Vinegar removes both smells and stains.
The Ammonia Method: Ammonia can also remove cigarette tar and nicotine from walls when mixed with water. Combine a tablespoon of ammonia for every cup of water, or roughly 1/2 cup of ammonia to a gallon of warm water. For painted walls, reduce the mixture to 1/4 cup to a gallon of water. For a stronger solution, increase the ammonia to a full cup. Apply the cleaning agent directly to the wall and let it sit for about five minutes before wiping it off. Follow with a clean rinse of warm water.
For stains, we’ve also suggested a bleach and water mixture. Don’t forget to replace the air filters in your home, too. They can also be stink traps.
Replacing your carpets is obviously the best solution for removing the odor they’ve absorbed over time, but that’s not realistic for most of us. It’s an expensive project, and if you’re a renter, your landlord might not comply. To remedy stinky carpets, sprinkle baking soda on them and let it sit for a while—perhaps even overnight. Then, thoroughly vacuum the carpet and the baking soda along with it. If that doesn’t get the job done, you might need a deeper clean. Rent a carpet cleaning machine or steam cleaner. Typically, you fill it with cleaning solution (or white vinegar and water for a cheaper solution) then run the machine up and down your carpets, as you can see in the video above.
Your dishwasher is filthy
Your dishwasher needs a simple cleaning every month or so, and it’s as easy as running the dishwasher empty with a cup of vinegar. Alternatively, you could sprinkle some baking soda across the bottom of the dishwasher and run it. The video above will show you how it’s done.
Beyond the basics, however, every dishwasher needs an occasional deep cleaning, and if yours smells like gross, old food, it’s probably high time for a scrub down. Focus on two areas: the seals and the dishwasher trap.
Find the trap (or filter) under your dishwasher’s sprayer. If you haven’t cleaned it in a while, you might find scraps of food and other gunk. Sometimes the tray comes out so you can just rinse it in the sink. If not, you’ll need a towel to remove the gunk build-up.
Second, wipe down the rubber seal around the dishwasher door. Use a vinegar and water solution to get rid of any mold or buildup around the area.
A dead animal is decomposing somewhere in your home
I’ve never (knock on wood) dealt with the reportedly pungent, sickly smell of a dead critter in my walls or ceilings, but from what I understand, it’s tough to ignore.
Most likely, the smell will be knock-you-out strong in one particular area, and that should be able to help you identify the source, whether it’s in the attic, basement, or some specific wall. Wildlife Removal points to some common areas:
The attic: It can be tricky to find the culprit in the attic because it might be buried under the insulation. They explain that when an animal dies in the attic, it’s common for the smell to permeate the whole house.The wall: Yep, sometimes animals live in your walls or fall down in them and get stuck and die. Experts sniff out the spot, cut a hole, remove the carcass, and patch it up.The chimney: It’s rare, but it can happen, particularly if you have a metal chimney flue that the animals can’t climb out of.Under the house: Animals of all kinds—raccoons, opossums, and even cats—often live under elevated houses and die in the crawl space.
They add that people often think there’s a dead animal in their ductwork, but that’s actually very rare. Usually, it’s just the airflow stirring up the smell. As we’ve pointed out before, if you’re going to remove the carcass yourself, some cities have guidelines they want you to follow, so check with your city’s sanitation department.
Speaking of cleaning up, removing the carcass might not be enough. Clean the area thoroughly to get rid of any remains or smell left behind. Do My Own Pest Control recommends the following:
If you are able to remove the animal carcass you will be able to eliminate the odor quickly by using products like Bac-A-Zap or Odor Hunter that utilize enzymes to break down the offending odor-carrying molecules. These products should be sprayed onto the area (or as close to the area as possible) where the odor originated from to be effective. You may also use the Earth Care Odor Remover Bags. These bags are simply hung up in smelly rooms and as the air in the room passes through the bag, the odor is removed.
If the carcass is in an inaccessible area, bring in a pro. Call your local pest control or wildlife removal company to help you identify the location and remove the source and clean up the area. If you have the DIY skills, you could try it on your own, though. In the above video, wildlife control specialist Shinya Coulter removes sheetrock from inside of a closet to get to a dead rodent (thankfully, Coulter doesn’t show it), then he simply patches up the hole, which we’ve shown you how to do here.
You have electrical problems
I fried fish once, and the smell lingered so long, I thought something was amiss. Turns out the fish just really stuck, but in my research, I learned that malfunctioning electrical wires often emit a stinky fish smell.
Maintenance company Boulden Brothers explains:
Electrical shielding, wires, and other plastic components emit a “fish” or “urine” smell when exposed to high heat. If you smell something fishy, go around your home and look for outlets and other electrical equipment that looks burnt or melting. Also, make sure that plastic and anything else that could burn is far away from any heat source, including light fixtures.
Electrical problems can be dangerous, so if you suspect your home’s wiring is faulty or its electrical components are overheating, call a licensed electrician. Many professionals aren’t familiar with the “fishy smell” problem, but any good one should have an infrared camera to help pinpoint heat sources.
Sewage gas is seeping into your home
Sewage and rotten eggs share a similar putrid aroma, and a rotten egg smell might indicate a gas leak, which is a lot more dangerous. If you smell rotten eggs and you suspect it might be a gas leak, exit the area, make sure not to turn on any lights or use anything ignitable, then call your gas company. Pacific Gas & Electric offers a more detailed gas safety guide here.
Other than that, if one part of your home—typically the bathroom—just smells like sewage, it might just be a dried up P-trap.
P-traps are designed to trap water in the pipe, creating a seal that prevents sewer gas from leaking up through the sink or bathtub. If you haven’t used your sink in a while, the water in the P-trap evaporates, eliminating that barrier. In other words, sewage gas passes right on through, stinking up your bathroom. Similarly, gasses can escape when the water level in your toilet bowl drops. The remedy? Simply flush your toilet or run your sink or bathtub for a bit to clear the pipe.
In some cases, though, you might have a more serious problem in your sewer, drainage, or venting pipes. As Home Guides explains, your toilet could be cracked or your vent pipe could be clogged. In those cases, you’ll probably want to call a plumber, although Home Guides does offer steps for fixing the problem if you’re a DIY-er.
Your water heater needs maintenance
While you’re checking your P-traps, you may also want to check your hot water heater. As Water Tech Online explains, In places where there’s a lot of sulfur in the water, the agent used to reduce the sulfur often reacts with the anode rod in the water heater.
Replacing the standard anode with an aluminum/zinc anode, provided that no water softener is being used, often works in this situation because the reduced current of the anode will significantly reduce the amount of H2 gas generated in the tank.
Run your hot water and see if the smell is more prevalent. If so, you may need a new anode rod, which experts suggest you replace every five years, anyway. Just make sure to read your water heater’s warranty, because some of them require specific types of rods, otherwise the warranty could be voided.
You can call a plumber or appliance repair specialist to replace the rod, or give a go yourself. The above video shows you how it’s done. Again, there’s a big difference between a faint smell coming out of your sink and the strong odor of a gas leak (which might be accompanied by a hissing sound), so be sure to take the necessary precautions if you suspect a natural gas leak.
Home odors can be subtle and tricky. Sometimes they’re faint and they creep up on you over time, making them hard to pinpoint. These common household issues are often culprits, so watch out for them and you’ll be on your way to a stink-free home.
This story was originally published June of 2016 and was updated in 2019 with new photos and to reflect current links and information. Updated again March 15, 2021 with a new header image and to reflect current style guidelines.