How to find and fix a bad smell in the house

A bad smell in a house is rarely in one place, and it is almost never fixed by covering it up. Smells come from food, drains, damp, pets, trash cans, appliances and the air-conditioning, and each leaves its own clue. The first job is to describe the smell accurately and find where it is strongest. The second is to match the smell to its likely source. Most smells are harmless, though unpleasant, and they clear once the source is cleaned. A few smells, particularly rotten egg and gas smells, are a safety matter and need action at once.

Safety first: gas and sewer gas

Before you start looking, check for two smells that are dangerous.

A rotten egg smell that is strong, sudden or near a gas appliance is likely to be gas. Utilities add a strong odor to natural gas so that leaks can be noticed. If you smell gas, leave the building straight away. Do not switch lights on or off, do not use the phone inside, and do not light anything. Once you are outside and away from the building, call the emergency line for your gas utility, or the emergency number for your area. Stay out until you are told it is safe.

A sewage or rotten egg smell from a drain is usually sewer gas. It is unpleasant and it can be a health hazard in an enclosed room, so it needs fixing. Start with the traps, described below. If the smell persists after you have run water into every drain, call a plumber, because a blocked or badly vented drain can let sewer gas into the house.

Describe the smell

Before you start searching, note the answers to these questions. They narrow the list quickly.

• What does it smell like? Sour and rotten suggests food. Musty and damp suggests mold or water. Sewage or rotten eggs suggests drains. Burnt suggests an appliance or wiring, which needs a check by an electrician. Ammonia suggests urine.
• Where is it strongest? Near a sink, a trash can, a cabinet, a vent, or a particular room?
• When does it appear? After rain, after cooking, after a wash, or all the time?
• Does it change? A smell that comes and goes often means a drain or a trap that dries and refills, or a fan that cycles on and off.

Drains and traps

Drains are the most common source of a sudden bad smell, and most of them are easy to fix.

1. Run water into every drain you do not use often: the spare bathroom sink, the floor drain, the shower in a guest room. This refills the trap, which is the U-shaped bend under the sink that blocks sewer gas. A dry trap lets the smell straight up.
2. Pour a cup of boiling water down the kitchen and bathroom drains to loosen grease and soap. Repeat if the smell is strong.
3. For a stubborn drain, pour half a cup of baking soda down the drain, follow it with half a cup of white vinegar, cover the drain for about thirty minutes, then flush with hot water. The fizzing helps loosen the film inside the pipe, though it does not clear a serious blockage.
4. Use a plunger on a sink or a bath, or a drain brush on the first few inches of pipe, to remove hair and soap that have built up.
5. For a drain that keeps smelling, use an enzyme drain cleaner, which breaks down organic matter in the pipe over time. Follow the label, and do not mix it with other drain products.

Do not use strong chemical drain cleaners that contain lye or acid at the same time as any other product. Mixing them can release dangerous gases or cause burns, and it can damage the pipes.

The kitchen

Kitchen smells usually come from food that has gone off somewhere you cannot see, or from the appliances that handle food.

• The trash can and the food waste. Clean the trash can, the lid and the surrounding floor, and empty food waste more often. A sealed bag and a clean liner stop most of the smell.
• The garbage disposal. Grind ice and a few pieces of citrus peel with cold water to clean the blades and the walls. Run the water while it runs, and clear any food caught in the chamber with the disposal switched off.
• The dishwasher. Trapped food in the filter is the common cause. See the dishwasher guide for the full routine.
• The refrigerator. Check the drawers, the drip tray and the door seal, and throw out anything that has gone off. The refrigerator guide covers the cleaning steps.
• The sink and the cloths. Dish cloths and sponges hold bacteria and food. Wash them hot, dry them fully, and replace them often.

Bathrooms and damp

A musty smell in a bathroom or a closed room is usually damp, and the cause is almost always moisture that is not getting out.

• Run the exhaust fan for twenty minutes after a shower or bath, and check that it actually moves air. A fan that is clogged with dust or that vents into the attic will not clear the damp.
• Check the cabinets, the baseboards and the space behind furniture against an outside wall. Mold that is hidden in these places produces a strong musty smell long before it is visible.
• Look at the seals around the bath, the shower tray and the window frames for cracks or gaps where water gets in.
• Use a dehumidifier in a damp room, and keep the door open to let air move.

For mold on surfaces, use the methods in the mold guides. For mold behind walls or under floors, or mold that covers a large area, call a specialist.

Laundry and textiles

Smells from laundry usually come from the washing machine itself, from damp laundry left in the drum or the basket, or from towels and bedding that are not drying fully. The washing machine and towel guides cover the cleaning steps. Check the machine’s door seal and drawer, dry the laundry quickly, and do not leave wet items in a closed basket.

Upholstery and carpets can hold smells for years if they are not cleaned properly. A sofa that smells of smoke or pets, or a carpet that smells of old urine, needs the cleaning methods in those guides, not an air freshener.

Pets

Pet smells come from urine, feces, bedding and litter. Clean the litter tray regularly, wash the bedding in hot water, and use an enzyme cleaner on any accident on the carpet or the floor. Ammonia-based cleaners can encourage repeat marking, so use an enzyme product instead. The carpet and litter guides give the steps.

Air conditioning and ventilation

A musty smell that comes through the vents when the heating or air conditioning starts can come from mold in the ducts, the drip tray of an air conditioner, or a dirty filter. Change the filter on the schedule in the manual. Check the drip tray of any air conditioner, and clean it if it is dirty. If the smell persists, or if you can see mold in the vents, call a heating and cooling technician, because duct cleaning and mold removal need the right equipment.

Smoke

Cigarette smoke and cooking smoke cling to fabric, paint and ceilings. Ventilate the room well, clean fabrics and curtains, and wipe hard surfaces with a damp cloth. Wash the walls and ceilings if the smoke has stained them, using a mild detergent. Air fresheners and ozone generators do not remove smoke, and ozone can irritate the lungs, so avoid using them to cover a smoke smell.

Using ventilation and baking soda

Good air movement does more than any product. Open windows on opposite sides of the house for a few minutes each day, and run the exhaust fans in the kitchen and the bathroom. Baking soda in an open dish absorbs odors in a closed room, and it works well in a refrigerator, a cabinet or a closet. Replace it every month or two.

When to call a professional

Call a plumber if a drain smell persists after you have refilled the traps and cleared the drains, or if you suspect sewer gas. Call an electrician if you smell burning or hot plastic, and turn the power off at the breaker box if it is safe to do so. Call a gas technician or the gas utility for any gas smell, and do not wait. Call a specialist for mold behind walls or under floors, and for a smell from the ducts that persists after cleaning.

Most house smells are solved by finding the source, cleaning it properly, and letting the house air out. The rule to remember is that a smell is a clue, and the clue points to the place that needs attention.