Ask Alec: Why Does Carpet or Upholstery Smell Different When It Gets Wet?
Have you ever wondered why carpet smells when wet, even though it may have little or no noticeable odor when it is dry? There can actually be several explanations, and after more than 56 years of cleaning carpets and upholstery, I’ve learned that the answer isn’t always as simple as it may seem.
Why Carpet Smells When Wet
One of the things I notice most often is that a heavily soiled carpet can develop what I would describe as a “wet dirt smell” when it becomes damp.
That doesn’t necessarily mean the cleaning caused the odor. Moisture can simply make odors from materials that have accumulated in the carpet much more noticeable.
Think about everything a carpet encounters during its lifetime. We walk across sidewalks, parking lots, stores and countless other surfaces every day. We also walk through places such as public restrooms. Whatever is picked up on the bottoms of our shoes can eventually be tracked into our homes.
Carpet also collects food particles, body oils, dust and many other substances through normal everyday use. Microorganisms are naturally present on the surfaces around us and in the air we breathe. Under favorable conditions, moisture can make odors associated with some of these materials more noticeable.
This is one reason I have always believed that carpet cleaning is about more than simply making a carpet look clean.
Moisture and Humidity Can Make Odors More Noticeable
Humidity is another factor that is often overlooked when people wonder why carpet smells when wet.
Many odors become more noticeable when something is damp or when the surrounding air is humid. The longer a carpet remains damp, the longer those odors may remain noticeable.
I’ve seen this many times in homes with finished basements where there is no air conditioning. These areas can have higher humidity and less air movement than the rest of the home. As a result, carpets can take considerably longer to dry.
When possible, I will sometimes recommend that customers with finished basement rooms consider having their carpets cleaned during the winter months, when the indoor air is generally much drier. Faster drying can make a significant difference.
Drying time isn’t the same for every carpet. It can be affected by the amount of soiling, the thickness and construction of the carpet, the humidity in the home, ventilation and air movement, the equipment being used and the way the cleaning is performed.
In other words, there isn’t one drying time that applies to every carpet.
Sometimes You’re Smelling the Carpet Fiber Itself
A heavily soiled carpet may smell very different when wet than a relatively clean carpet.
Here’s something I’ve learned simply from spending decades around different types of carpet:
Not every odor you notice when a carpet is wet comes from dirt.
Different fibers can have their own characteristic odors when they become wet.
Wool, for example, has a very distinctive natural odor when wet. I’ve cleaned enough wool carpet over the years that I can recognize it almost immediately.
Other natural and regenerated fibers, including cotton, linen, rayon and silk, can also have their own distinctive odors when they become wet.
That means a relatively clean carpet may smell very different when damp than a heavily soiled carpet. With heavily soiled carpet, you may notice that “wet dirt” smell. With a cleaner carpet, the odor may be much more related to the fiber itself.
This is something that is difficult to appreciate unless you’ve spent many years working with different carpet fibers.
What About Upholstery?
The same basic principle applies to upholstered furniture, but there is an important difference in how upholstery should be cleaned.
When upholstery is professionally cleaned, moisture should be carefully controlled.
The objective is to clean the outer fabric while carefully controlling the moisture so that it does not unnecessarily penetrate into the cushion and its underlying materials. Whether the cushion contains foam, down or another filling, the cleaning process should use the appropriate amount of moisture for the particular fabric and construction.
So if a customer notices a different smell while their sofa or chair is damp, I would not automatically assume that the odor is coming from the material inside the cushion.
The fabric itself, materials that have accumulated on or within the fabric, the cleaning solution and the humidity in the room can all influence what you smell while the upholstery is damp.
What About Cleaning Solutions and Deodorizers?
The cleaning solution itself can also contribute something to the overall smell immediately after cleaning. Many cleaning products have a mild scent.
Then there is the use of deodorizers.
Some cleaners routinely offer or recommend adding a deodorizer to the cleaning process. A deodorizer can certainly make something smell more pleasant, but there is an important distinction between adding a fragrance and removing the source of an odor.
In my opinion, if the source of an odor can be addressed through proper cleaning, that is preferable to simply covering it with a strong fragrance.
I’ve also found over the years that technicians can become somewhat desensitized to the strength of the products they work with every day. What seems like a pleasant fragrance to someone who works around it constantly can be overwhelming to a customer who encounters it only occasionally.
Sometimes less is more.
Does “Steam Cleaning” Disinfect Carpet?
There is another subject that comes up whenever we talk about moisture, heat and microorganisms.
You will sometimes hear carpet cleaners promote their equipment by saying that the high temperatures produced by their truckmount equipment will disinfect or even sterilize carpet.
I would be very cautious about making that assumption based on temperature alone.
There is an important difference between the temperature a machine can produce and the temperature actually delivered to the carpet. There is also the question of how long a particular temperature remains in contact with the material.
True steam sterilization is a controlled process involving steam, temperature, pressure and time. The CDC’s guidance for steam sterilization, for example, describes specific temperatures and exposure times used in sterilization equipment.
That is very different from simply saying that a carpet-cleaning machine produces water at 220 degrees.
There is also an important distinction between cleaning, sanitizing, disinfecting and sterilizing. These terms should not be used interchangeably.
The EPA has specific guidance concerning antimicrobial claims for soft surfaces, including carpet, rugs and upholstery. Such claims depend on appropriate testing and the particular product and method being used.
Professional carpet cleaning is primarily intended to remove soil and other contaminants. I would not tell a customer that simply cleaning their carpet with hot water has made the carpet sterile.
Cleaning is not the same thing as sterilization.
Why I Started Thinking About This Many Years Ago
Long before the internet and long before today’s carpet-cleaning terminology, I put a slogan on my company’s business cards and stationery:
“Dirt breeds germs, call for the health of it.”
I came up with that slogan because I understood even then that what accumulates in a carpet isn’t necessarily just something that makes the carpet look dirty.
Our homes are not sterile environments, and they shouldn’t be. Microorganisms are naturally present around us. But that doesn’t mean we should ignore the accumulation of soil and other substances in the carpets and upholstery where we live.
My son studied biology and was just short of a double major in biochemical science. His first job after college involved a company that grew replacement skin for people who had suffered serious burns or other injuries. Because that tissue was being grown in laboratory conditions, controlling microorganisms in the environment was extremely important.
That experience reinforced something I had understood for many years: there is a tremendous difference between an ordinary home environment and an environment where microbiological contamination has to be carefully controlled.
A carpet in your home is certainly not a sterile laboratory environment, nor does it need to be.
But after more than five decades in this business, I’ve learned that cleaning is about much more than appearance.
So, Why Does Carpet Smell When Wet?
The next time you notice that your carpet or upholstery smells different when it becomes wet, don’t automatically assume that something went wrong during cleaning.
You may be smelling the carpet fiber itself. You may be noticing odors from soil or other materials that have accumulated over time. Humidity and moisture may simply be making an existing odor much more noticeable. Or the cleaning products themselves may temporarily contribute to the overall smell.
And sometimes, particularly with heavily soiled carpet, you may simply be experiencing what I call the “wet dirt smell.”
After 56 years of cleaning carpets and upholstery, I’ve learned that understanding these differences is part of understanding how to properly clean the material in the first place.
If you have a question about carpet, upholstery or area-rug cleaning, Ask Alec.