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What is that terrible odor?

Skunk image; odor

There is an old story that I tell that goes like this.  I am sent to a home where the owners have noticed a strange odor that they want us to identify.  As soon as I enter the door, I am immediately asked “Can’t you smell it?  Can’t you smell it?!!”.  After sniffing around for a few moments, I tell the owners “I smell the oregano from last night’s dinner, I smell the dog, I even smell some wet towels.  But I don’t quite know yet what you are smelling.”

And that is the problem with odor detection.  In truth, every home has its own unique smell, but our minds have the ability to block it out.  We can block out certain odors that we deem to be “normal”, but other odors can stand out and drive us crazy.  What exactly is that odor?

Odors can come from a wide variety of sources.  So in dealing with an unusual odor it’s best to ask some questions.  One question involves asking “what does it smell like?”  At first blush, this seems like a very obvious question.  However, during the last year I have investigated at least eight homes where the owners thought they smelled mold in the property.  In reality, what they smelled were odors associated with a natural gas leak.  In another case, a client noticed that his coats and sweaters had an unusual odor.  He thought it was mold, but in reality it was a heavy stain on his hardwood floor.  

So ask yourself these questions: is the odor that I am smelling “musty” (like in an old basement) or does it have a more “chemical” smell.  Musty odors are usually associated with mold, whereas chemical type smells can be associated with volatile organic compounds (VOCs) that are often affiliated with building materials.  A “rotten egg” smell could be hydrogen sulfide from sewer gas.

Another question that you can ask yourself is “when did you first notice this odor?”  Let’s say that you noticed the odor roughly two months ago.  During that time, what changed in the home?  Did you have a flooding event in your basement?  Did you have some remodeling done in a particular area of the house?  Was there a dead animal somewhere in the property?  Did you switch from heating to cooling?  At first we may think that the odor just suddenly appeared, but in truth we can usually connect it to some event.  

We may also ask, “is the odor particularly worse at a certain times of the day or week?”.   Some clients have noticed that there is a cigarette smell that they suspect comes from a neighbor in an apartment building.  Does the neighbor have a tendency to smoke in the morning?  Late in the evening?  There are some clients who live above a commercial property where they run certain machines or use various chemicals at specific times.  In this regard, it may be best to keep an odor log to see if there are any discernable patterns.      

Once we have determined what the odor is, the next logical question is ‘How do I get rid of it!”  Depending on the source… it depends.  If the odor is musty, then it is highly likely that it is coming from mold or bacteria and the best way to eliminate the smell is to fix the underlying moisture problem and clean the area.   If the odor is coming from a VOC, the solutions can be a little more complex.  If removing the source is too expensive or not feasible, outdoor air ventilation is typically best.  Ventilation is a fancy way of saying open up the windows and allow as much fresh air as possible to flush the area of concern.  I often times recommend having box fans in windows to blow good air in and bad air out.  

So the next time you think to yourself “What on earth is that terrible smell?”, think about some of the questions that I mentioned above.  If all else fails, consider having Indoor Science examine your property for a more thorough investigation.

Ian Cull

Ian Cull is a nationally recognized expert in the field of indoor air quality. He is the Chief Science Officer of Indoor Science, a company he started in 2004. He speaks around the world on air quality topics and is a training provider of the Indoor Air Quality Association. Mr. Cull is a Licensed Professional Engineer (PE) and Certified Industrial Hygienist (CIH). His degree is in Environmental Engineering from the University of Illinois - Urbana Champaign. Mr. Cull has developed 50 air quality related courses for the IAQA University and is the author of the book, “Fundamentals of Mold Remediation”. In his words… “Besides being passionate about indoor air quality, I enjoy cycling, music, the Chicago Bulls, and having fun with my three kids.”

7 thoughts on “What is that terrible odor?

    I have a gas odor so noxious in my townhome since I bought it in 2014. The odor erupts unpredictably. It erupts in all seasons and weather conditions and not always constant enough to get a contractor to come in to smell it. It was ruled out as natural gas and sewer gas. It seeps in from only one outside wall at the floor board gaps in my bedroom and my dining room (both room shared the same outside wall). A mold inspector came in and said it didnt’ smell like mold to him. An animal trapper was hired by my HOA and he came when the odor was bad. He couldn’t identify it as decay of any kind of animal or insects. Then at my HOA’s urging, the animal trapper came two days later to pour a liquid neutroleum alpha with strong fragrance into an eroded hole on the outside of my foundation right next to the hole my air conditioning unit pipe enters – right under the floor of my bedroom where the odor comes in from the floor board. So now the gas odor is mixed with the fragrance in my bedroom. Because of the fragrance from the chemical is strong in the bedroom, the gas odor is now more prominent in the dining room away from that concrete hole. It seeps into my house from the dining room floor board gap, just like my bedroom. What should I do when the fragrance is still present and may be hard to have the actual gas odor tested. Please advise. Thanks.

    I work in a three story atrium office building. A few weeks ago I began smelling what seemed to me like car exhaust. I am in the southeast corner of the second floor but those about halfway down the office going west smelled what they thought was gas. There is no gas line to the building so I know it isn’t gas. I have questioned the owner to check the HVAC to ensure it is properly vented. Last night on my way out I met the maintenance man in the elevator and when we both stepped off on the first floor in the atrium we both commented on the smell and that I thought it was exhaust and he thought it came from the HVAC venting (he is not a HVAC tech, he does general maintenance). I called the owner and he came out this morning and said he had spoken with the other tenants and they don’t smell anything and neither does he. That he has had the HVAC service group out and they say the unit is fine. I told him he needed to contact a company like yours to have the air quality checked as there is definitely a smell and if it is due to engine exhaust of some kind it could be detrimental to anyone with respiratory issues. Have you run into any similar cases? Can your firm test for carbon monoxide?


    Is there an attached parking garage? Is there a kitchen in the building? Is the odor strongest near the elevators? Our firm can test for carbon monoxide and a whole host of other air quality issues. We are in Chicago. Are you in the general area?


    2 weeks ago, had Trafficmaster wood-like laminate put on basement floor. There is no odor in the basement; however, it is at my front door, which is one floor up and near a stairwell. Do odors from gassing off relocate like this?

    You are first smelling it at the top of the stairs, but I assure you the odor would be in the basement. You get used to it down there, but it hits you when you first catch a wiff upstairs.

    Is there a home device that detects and identifies, in my case a chemical odor in a 5 year old addition (12×22) of my house. Do LCD televisions emit odors (5 yrs old)


    There are no instruments that will identify what an odor is. An odor is a complex made up of chemical gasses and physical particles, and there is no easy way to track down many odors. I would not expect an LCD tv to cause odors.