Mold contamination has become the most common indoor air quality issue we encounter, both in commercial and residential buildings. Based on frequency, mold is followed by formaldehyde, other volatile organic compounds, and finally pesticides. We are often asked by clients how to recognize that a contaminant is present. This is not an easy question, but I will try to summarize the most common signs that occur in the residential home.
1. There is an odor that you can smell intermittently.
An intermittent odor almost always points toward a biological source, such as mold or bacteria.
The occurrence and intensity of the odor varies with the life cycle and level of activity of the organisms. All microscopic organisms require a steady source of food and water, and their level of activity will vary according to the availability of both. If the weather turns cool and dry, the odor and activity diminishes. On a warm and humid day, the activity and odor increase. The odor may go away entirely in the winter heating season, as the organisms sense that the dry season is upon them. It will likely return when the environmental conditions are favorable.
Odors that increase when it is raining outside suggest that the source of biological activity is also outside, perhaps in a wall cavity or in the attic. Microbial activity that depends on rainfall for its moisture is challenged, since sometimes it will be wet and sometimes dry. Most organisms do not like that variation and may not grow. If water is held in the wall cavity, let’s say by fiberglass insulation, that may be enough to sustain life until the next rain event occurs.
2. There is an odor that you can smell continuously.
A continuous odor frequently points to a chemical source. This is commonly experienced with a storage tank leaking heating oil, a new coat of varnish on the floor, or new furniture or carpet. If the compounds are low molecular weight and high vapor pressure, they may evaporate (off-gas) and leave the building pretty quickly. Many chemical compounds, however, are high molecular weight with low vapor pressures, and may persist indefinitely without intervention. The key issue here is that you can almost always smell the contaminant when you first enter a space. If it is always there, it is most likely chemical and not biological in origin.
3. There is an odor that I can smell initially and then it’s gone.
This phenomenon is not really related to the contaminant but to our olfactory limitations. Many contaminants are very evident initially and our nose can sense the odor at very low levels. Within seconds, however, our olfactory cells become saturated and we can no long sense the odor. Probably the most famous chemical with this property is hydrogen sulfide (H2S), which has the characteristic rotten egg odor. Initially most folks can small H2S at very low part per billion levels. (A part per billion is literally one molecule of a contaminant mixed in with 1 billion molecules of air). After about a minute we can no longer smell this very rotten odor. Workers actually die from H2S exposure and everyone wonders why he didn’t just leave Dodge. Well, he could not smell the H2S and thought he was safe. It is called olfactory fatigue but it never makes the newspapers as the cause of death.
Just as an aside, there is a second limitation of the nose that makes it an unreliable sensing tool. Our nose can smell some chemicals but not others. And it does not depend on the vapor pressure of the chemical. Vapor pressure is a measure of how fast the chemical evaporates. High vapor pressure = fast evaporation. Our ability to sense the chemical depends on how the chemical reacts to our olfactory sense. It’s known as the odor threshold of the compound. Most folks can easily sense some chemicals with low odor thresholds, such as perfumes and various sulfur compounds. Other compounds, such as carbon monoxide and methane, we can’t smell at all.
As a result of these limitations, I do not rely on my sense of smell when conducting an air quality survey. Good thing, since I can’t smell a thing after all these years checking out mold gardens.
4. I don’t smell or see anything, but my grandson always gets sick when he comes over.
This is another sign of microbial contamination that the folks living in the house can tolerate but others cannot. You would be surprised how many of our elders have lived with a moldy basement for years and don’t notice a thing. They may not even go in the basement. It may be that the mold slowly developed and the couple developed a tolerance, but the grandson did not.
This variable response (some do, some don’t) is characteristic of biological activity. It comes down to the nature of an allergic response. You may be miserable with a runny nose and tearing eyes, and I don’t notice a thing. Or Mom the hypochondriac has not been feeling well for a while, but Dad feels fine. I have seen some amusing cases where Dad was fine until he retired. When he spends more time at home, suddenly the question is “What’s wrong with this house?”
5. I am sick when at home but feel better when I’m on vacation.
This is a typical occurrence that also points to an allergic type response. If you are away from the offending contaminant long enough, your immune response recovers and the symptoms like runny nose, irritated eyes and skin rash subside. It is important that the new environment be sufficiently different from the home environment to make a difference. It doesn’t seem to work when the time away is short, such as going to work, or when the new environment is just as contaminated as home. You do not want to know how many hotel rooms, especially near the shore, harbor mold behind wallpaper and in air conditioning systems.
But when little Johnny comes over to visit Grandma and always ends up with a stuffy nose, it may be time to check out the basement and furnace unit.
6. The dog has a funny rash and looks generally forlorn.
This one is not entirely farcical, although I probably laughed after the first couple pet calls we got years ago. But pets such as dogs and cats have respiratory systems and skin just like us, and Fido could surely have an allergic response to a contaminated condition. It may be pure coincidence, but we usually find some kind of a microbial issue in homes where the dog or cat is sick. At the very least, the owner’s concern for his pet may motivate him to have the house checked, and the opportunity to diagnose a condition of concern. We cannot conclude that the condition accounts for Fido’s funky fugue, but we can state that finding and fixing a mold problem will make the indoor environment healthier for everyone.