Why Won't That Bad Smell Go Away? Understanding the Chemistry Behind Trapped Odors

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Why Won't That Bad Smell Go Away? Understanding the Chemistry Behind Trapped Odors

Wondering what that horrible pet urine or cigarette smell won’t go away no matter how much you scrub and spritz deodorizing sprays? Learn the chemistry behind bad odors to understand why odors get trapped in your home and how to get rid of them.

Understanding the Science Behind Smells

A smell is born when a substance releases vaporized, airborne molecules, which then travel through the air and into our noses. Molecules are two or more atoms that have bonded. Not all molecules have odors that we humans can detect, but many molecules, once they enter our nasal passages, are detectable. Some molecules have odors that are appealing to humans, and some are not.

When we smell an odor, we’re actually sensing vaporized molecules that have evaporated from the surface whatever substance we are smelling. The vaporized molecules bind with a specific set of olfactory receptors, triggering a signal in your brain that you interpret as smelling a particular odor.

Not all molecules vaporize with ease, which is why we can smell some substances very well and other substances not at all or only mildly. In some cases, humans simply don’t have olfactory receptors for that odor. For example, carbon monoxide and natural gas are odorless because human don’t have receptors sensitive to those two gases.

How Odors Become Trapped

Odors linger for multiple reasons, one of the most important of which is the substance's volatility, which means how easily the molecules vaporize (convert from a liquid to a gas). The more volatile a molecule is, the more of it becomes airborne—and the more likely you are to smell that odor.

Once those molecules vaporize, they look for homes in which to live. The materials with which those vaporized molecules come in contact influence how long odors remain. Fabric, hair, carpet, wood and even cement are all highly porous. Vaporized molecules settle into those pores and live there, bonding with the molecules that make up those porous materials.

Some vaporized molecules produce unpleasant odors don't like water, and some molecules such as those that make up fabric and carpet are also averse to water; in this case, the malodorous molecules cling to them because they share a similar aversion. These smells settle in deeply and last for a very long time, because they have bonded over a shared aversion.

Porous materials like wood, carpet and upholstery can hold onto vaporized odor molecules for months or even years. As long as the right conditions remain, the stench will stick.

Not All Molecules Are Created Equal

Not all odor molecules are the same. For example, esters cause a lot of fruity smells, and linear-terpenes produce a woody or sweet smell. Cyclic terpenes make up many of the floral scents, and alcohols, ketones, aldehydes and thiols are all common smells you would recognize. The unique chemical composition of each odor molecule determines how long they last, and where those odors can stick.

Think of cigarette smoke. Even if you wash your hands after smoking, the smell will remain on your skin. The chemicals and compounds in cigarettes make the smoke odor especially sticky. These vaporized molecules bind with your skin, clothes, walls, carpet, and upholstery. As such, the odor molecules in cigarette smoke are very difficult to eliminate.

The following are three compounds that cause some of the most common problematic odors:


Ammonia has a characteristic, pungent smell. Cat urine contains an impressively high amount of ammonia, which is why it smells so noxious and is so hard to remove. Why? Cats have incredibly efficient kidneys, which means cat urine is a highly concentrated solution containing urea, a compound composed of ammonia and carbon dioxide combined.


The smell of formaldehyde is noticeable at even low levels. This smelly gas gets into homes through particleboard and plywood, cigarette smoke, and some dyes and preservatives.

Cigarette smoke particles are especially hard to deal with because those particles can be as miniscule as .001% of the width of a human hair. That means cigarette smoke particles can penetrate almost any part of a house. Fabric molecules found in carpet and upholstery often contain lots of hydroxyl (cotton) or amide (nylon) functional groups that bind with molecules existing in cigarette smoke. This means the smell gets into the pores of the materials in your home and stays for a long, long time.

Sulfur Compounds

Dealing with rotten egg smells? That would sulfur compounds, specifically hydrogen sulfide. Well water is often the cause of this smell. Most people find sulfur smells to be particularly undesirable.

Understanding Professional Odor Removal Equipment: The Ozone Generator

The issue at hand is this: when you’ve got trapped odors, you need to do three things.

One, you need to open the pores of the materials that have trapped the odor molecules (carpet and upholstery fibers, hardwood floors, cement, drywall) in order to reach the odor molecules. This typically requires high heat.

Two, you need to convince those odor molecules to let go of the molecules they are currently bound to and attach themselves to ozone which will change the odor by changing the composition of the molecules. Here’s how that process works:

Ozone, which has three oxygen atoms, is highly unstable. When ozone is pumped into an area where odorous molecules exist, the ozone attaches itself to the odor molecules and oxidizes them into their basic elements—carbon dioxide and hydrogen. Want to know what’s wonderful about carbon dioxide and hydrogen? They are odorless! Your bad smells are now gone.

Before you try this yourself, you need to know that ozone is dangerous, and ozone generators can only be used in unoccupied spaces. Not to mention you have to heat the room up to over 90 degrees Fahrenheit for the ozone generator to open the pores of the materials in the room so the ozone generator can access the trapped odor molecules.

Third, it’s advisable to add a pleasant odor to the room after using an ozone generator. Here at E.R. Restoration Services of Charlotte, we use a pairing process that pairs the use of an ozone generator with mild odor replacement technology. That means you come home to a pleasant odor, not just an absence of all odors.

Understanding Additional Odor Removal Products: Anti-Microbial Products

In many cases, the trapped odors are related to bacteria and fungi.

Let’s say your child’s room stinks to high heaven of body odor. Perhaps your child is into sports, and after cross country practice he comes home, strips off those sweaty clothes, and leaves them on the carpet.

This warm, wet environment is a breeding ground for bacteria, mold, and mildew. The sweat contains proteins the bacteria need in order to thrive, which is what causes the bad odor.

The same sort of problem can happen when mold or mildew grow in a basement or bathroom where the warm, wet environment encourages the growth of fungi.

Eliminate the bacteria, mold, and mildew, and the odors will be eliminated as well. That’s what anti-microbial products do. They kill the microbial source of the odor, destroying bacteria and fungi. When the source of the odor is gone, the odor is also gone.

Need Professional Help with Odor Prevention?

Give us a call and we’ll help you determine what the best course of action is for your particular odor problems. Our team is ready to provide you with water and drainage service that can ensure bad smells never come from anywhere near your home. Though we don't offer restoration services, we can also put you in touch with a reputable company which does. Call us now to fix all your odor woes!

Article Summary

Quick question & answer: Why won’t that bad smell go away? How do I get rid of bad smells?

Some odors linger due to how volatile a molecule is. If it is more volatile, a larger amount of it becomes airborne, making it more pungent. Once vaporized, the molecules need to stick to a surface. Fabric, hair, and carpet offer prime places for them to settle into. Ammonia, formaldehyde, and sulfur compounds cause some of the most problematic odors. 

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