What's That Smell in My House!?
Updated: 2 days ago
Six common indoor odours explained
What Is That Smell in My House?
Six Common Indoor Odours Explained
It starts with a pause in the doorway. Something smells wrong, but you cannot place it. You empty the garbage, check the drains, inspect the refrigerator and look around the laundry room and pet areas. Nothing explains it. Opening the windows helps for a while, and you do another round of cleaning.
By the next morning, you notice that the odour returns. You are now checking vents, moving furniture and wondering whether the source is hidden behind a wall or coming from somewhere else entirely. What began as a nuisance is becoming both frustrating and unsettling.
That uncertainty is what makes indoor odours so difficult to investigate. A smell may tell you that something in the home has changed, but it rarely reveals the cause by itself. Unrelated sources can produce surprisingly similar odours, while air moving through rooms, wall cavities or ventilation systems can make a smell seem strongest far from where it began. The most useful question, then, is not simply, “What does it smell like?” but “Where and when does it appear, and what explanation fits the full pattern?”
This guide introduces six common indoor odour profiles and directs you to detailed guides for each one. These guides explore how the smell may be described, what can contribute to it and which observations may help narrow down the source:
These categories are starting points, not conclusions, and the list is not exhaustive. Fishy, fuel-like, chlorine-like, skunk-like, fragranced, cooking and outdoor odours may overlap these profiles or require a different investigation.
Before turning to the six odour profiles, it is important to recognize the warning signs that may require immediate action.
A Brief Safety Notes Before You Begin
Most household odours are not emergencies, but safety comes first.
Treat a rotten-egg odour as a possible natural gas leak until that danger has been excluded. Natural gas is odourless, so utilities add mercaptan (a sulfur-smelling odorant) to help reveal a leak. Énergir [1] advises avoiding flames and anything that could create a spark, leaving the building and calling 9-1-1 from a safe location.
Carbon monoxide, or CO, cannot be smelled, seen or tasted. If a CO alarm sounds, Health Canada [2] says to leave immediately and call emergency services from outside.
If you see smoke, flames or active sparking, or if a smoke alarm sounds, leave the building and call 9-1-1 from a safe location.
A warm or discoloured outlet, flickering lights, or a burning or rubbery odour near an appliance may still indicate an electrical problem. The National Fire Protection Association [3] recommends having these conditions inspected by a licensed electrician.
If strong fumes follow the mixing of household chemicals, move to fresh air. Health Canada [4] warns that some combinations can release harmful gases. Contact a poison centre or health care provider if you believe someone may have been exposed or harmed.
Once immediate hazards have been excluded, keep your observations safe and non-invasive. Do not open cavities, dismantle equipment or disturb suspected contamination without appropriate training and protection. Refer electrical, gas, plumbing or HVAC system concerns (heating, ventilation and air conditioning) to a qualified professional in the relevant field.
Improper investigation or removal can spread contamination, increase exposure, damage building systems or make the original problem more difficult to resolve.
When invasive or hazardous work is not required, begin by noting where and when the odour appears, what changed before it began and which conditions make it stronger or weaker.
1. Musty, Mouldy or Damp
Does it remind you of wet cardboard, old books or a damp basement? Perhaps it appears after rain or lingers inside a closet.
This is the place to explore moisture-related possibilities, including damp materials and belongings. A musty smell warrants investigation, but it does not establish that mould is present. [4]
Read the full guide: Musty Odour: Moisture, Mold or Another Cause?
2. Sewage, Sulfur or Rotten Egg
A rarely used bathroom, near a floor drain, at an unused basement sink, in a laundry room or utility room, after a shower runs, when a toilet is flushed, or when water runs at a sink may be where you first notice this smell.
Once a possible gas leak has been excluded, possible sources include plumbing defects, drains that have lost their water seal and wastewater residues. Water itself can also carry a rotten-egg odour. Distinguishing a room-based smell from one associated with running water helps direct the search. [5] [6]
Read the full guide: Sewage Odour: Start With the Drains
3. Chemical, Paint, Plastic or Solvent-Like
The room looks finished, but it now smells sharp, sweet or glue-like. Or an unfamiliar chemical smell appears without an obvious renovation.
Paints, adhesives, furnishings, cleaners and stored products can release VOCs (volatile organic compounds, chemicals that evaporate into indoor air). Some VOCs give off distinctive odours, while others may be present even when no odour is noticed. [7]
A recent purchase, renovation or product use may provide useful context for the investigation. However, the smell alone does not confirm which product or compound is responsible.
Read the full guide: Chemical Odours: Paint, Plastics or Something Else?
4. Urine or Ammonia-Like
You have cleaned the spot, but an old urine smell remains. Is a pet returning to the area, or did earlier contamination reach beneath the surface?
Carpet padding and underlying flooring can retain contamination that surface cleaning does not address. [8] The dedicated guide also considers litter areas, bedding and cleaning products that may complicate the picture.
Read the full guide: Why Does My House Smell Like Ammonia?
5. Smoke, Burning or Overheated Material
First, rule out an active fire or electrical problem. If you see smoke, sparks, melting material, scorch marks or unusual heat, stop using the suspected appliance or equipment and treat the situation as a potential fire hazard.
If there is no immediate danger, look at the pattern. Does the smell linger after cooking, appear when the furnace starts, or return whenever a particular appliance operates? These clues can help determine whether the source is residual smoke, overheated material, electrical equipment or another combustion source.
Possible sources include smoke residue, heating equipment and electrical components. Burning, rubbery or overheated-appliance odours, flickering lights and discoloured outlets should be evaluated by a qualified electrician. If there are signs of an active fire, follow the safety instructions above. [3]
Read the full guide: Burning Smell Indoors: Smoke, Electrical Problem or Overheating?
6. Decaying, Rancid or Dead-Animal-Like
A sour, putrid or sickly sweet smell can make you suspect a dead animal. Forgotten food and accumulated waste deserve consideration too.
If accessible food and waste sources do not explain the odour, signs of pest or wildlife activity may help direct the search. The presence of blow flies or maggots indoors can indicate that an animal, such as a rodent or bird, has died in a wall or attic. [9]
Other wildlife can also enter buildings. The Pacific Northwest National Laboratory notes that animals ranging from sparrows to raccoons can use openings around soffits, vents and crawlspaces. [10]
Read the full guide: Dead Animal Odour: How to Recognize Decomposition
Still Unsure Where to Start?
You do not need to identify the source before asking for help. For a persistent, non-emergency odour, a qualified investigation can review the building’s condition, recent changes and the pattern you have noticed, then determine whether measurements would be useful. [11]
Knowing where the smell appears, when it returns and what you have already checked gives an investigation a useful starting point.
Questions About a Persistent Dead-Animal or Decaying Smell?If the source remains unclear or appears concealed, an indoor air quality assessment can help identify practical next steps and determine which professional should investigate further. |
References
[1] Énergir. Contact Us: Emergency. Explains that natural gas is odourless, that mercaptan is added to help detect leaks and the actions to take when a leak is suspected.
[2] Health Canada. Carbon Monoxide: Preventing Exposure. Explains that carbon monoxide cannot be seen, smelled or tasted, and outlines how to respond to a CO alarm.
[3] National Fire Protection Association. Educational Messages Desk Reference. Covers emergency fire response and electrical warning signs, including burning or rubbery odours, flickering lights and warm or discoloured outlets.
[4] Health Canada. Guide to Addressing Moisture and Mould Indoors. Discusses moisture sources, damp materials and the investigation of possible mould-related concerns.
[5] Peel Region. Sanitary Sewer Smoke Testing. Explains how water-filled plumbing traps help prevent sewer gas from entering a home and how smoke testing can identify certain plumbing defects.
[6] Agency for Toxic Substances and Disease Registry. Public Health Statement for Hydrogen Sulfide. Describes hydrogen sulfide’s rotten-egg odour and its possible presence in well water and water heaters.
[7] Health Canada. Volatile Organic Compounds. Identifies household products and building materials that can release volatile organic compounds.
[8] Ohio State University, Indoor Pet Initiative. How to Clean Up Cat Urine. Notes that persistent carpet odours may require attention to carpet padding and underlying surfaces.
[9] Iowa State University Extension and Outreach. Blow and Flesh Flies. Explains that blow flies or maggots inside a home can indicate that an animal, including a rodent or bird, has died within a wall or attic.
[10] Pacific Northwest National Laboratory. Screens and Other Deterrents for Birds, Rodents, and Other Pests. Explains that animals ranging from sparrows to raccoons can enter buildings through openings around soffits, vents and crawlspaces.
[11] Health Canada. Guidance for Indoor Air Quality Professionals. Explains how inspections, monitoring and targeted measurements can be selected to address a particular indoor-air concern.
About the authorJohn Slavich is the founder of Puritas, an indoor air quality investigation service in Greater Montréal. He holds a B.Sc. in Physics, a master’s degree in engineering and several IICRC certifications. His mold investigations draw on the BNQ 3009-600 standard. He holds RBQ general contractor licence 5795-5080-01. |
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