Why Do Odors Cling to Things and Why Do They Come Back?

G. Kayra Oğuz, Chemical and Biomolecular Engineer · Last updated: September 15, 2026

Odor doesn't stay in the air, it settles somewhere

On the previous page I wrote that if you can smell it, the molecule is inside you. The same sentence has a version for your belongings: if you can smell it, the molecule is inside your home. Not in the air; in the fabric of the sofa, in the folds of the curtain, in the paint on the wall.

When cigarette smoke fills a room, the molecules do not settle for the air. As long as the concentration in the air is higher than on the surface, molecules keep moving onto the surface; the flow continues until the two sides even out. Chemistry calls this adsorption: a molecule clinging to a surface.

Then you open the window. The molecules in the air leave and the room clears. But the reservoir on the surfaces stays as it was; with the balance upset, the flow reverses and the molecules slowly mix back into the air. When you close the window, the room smells again.

That does not mean airing out fails. It works; it just empties the wrong reservoir.

Which surfaces hold odor, and why?

Surface	Why it holds odor	What to do
Curtains, upholstery fabric, mattresses, carpets	The large surface area and pores between the fibers trap the molecule	Wash what can be washed; on what can't, apply spray once it is dry
Painted plaster walls, ceilings	The paint film and plaster are porous; oily residue (cigarettes, soot, frying) sticks directly	Wipe with soapy water or with Multi-Purpose Liquid added to the cleaning water
Wood, particleboard, kitchen cabinets	Porous structure; odor seeps in through cracks in the varnish	Wipe the surface, place a gel in the small enclosed space
Foam, mattress padding, cushions	Open-cell structure that holds both the molecule and moisture	Dry it, apply spray on top, air it somewhere in direct sunlight
Car upholstery, headliner	Enclosed space plus heat; the molecule is released again and again	Clean the surfaces, then keep a gel in the cabin of the parked car
Refrigerator gasket, silicone sealant	Folds and pores draw liquid in	Clean with a toothbrush, wipe dry, then spray
Glass, metal, tile, glazed ceramic	Non-porous, so odor hardly clings at all	Regular cleaning is enough

The difference in one sentence: porous, oil-loving surfaces hold odor; smooth, non-porous surfaces don't. That is why the grout between kitchen tiles smells while the tiles themselves don't.

Why does an odor sometimes come back all of a sudden?

There are two triggers.

Heat. As temperature rises, molecules leave the surface for the air faster. When you turn on the heating, when the sun hits the living room, when the car sits in the sun, an odor that had settled in comes back at once. A summer house that stays closed up smells sharp for the same reason.

Humidity. Water molecules enter the pores of the surface and take the place of the molecule clinging there, which then moves into the air. That is the musty smell getting stronger on a rainy day, and the bathroom odor standing out after a shower.

So the odor is not "coming back"; it was there all along, only the release rate changed.

Why do some odors last for years?

Three reasons stack up:

1. Oily residue. Cigarette smoke and frying soot leave more than odor molecules; they stick a thin film of oil and tar onto the surface. That film smells on its own and also becomes a layer that holds new molecules. Wiping with a dry cloth does nothing; you need something that dissolves the oil.
2. The source is still active. If the sink trap has dried out, if the refrigerator drain hole is clogged, if the spot the cat marked has not been cleaned, the odor keeps being produced. In that case no product gives a lasting result.
3. There is a reservoir you haven't reached. Under the sofa, behind the cabinet, the inner face of the headboard, the felt under the car seats. This is usually why you can clean ninety percent of a room and still not be done with the odor.

The right order

1. Remove the source. Sink trap, clog, spoiled food, dirty litter, wet textiles. This comes first.
2. Wash. Everything washable goes into the machine; walls and hard surfaces get wiped with Multi-Purpose Liquid added to the cleaning water.
3. Dry. A damp surface both holds odor and feeds mold.
4. Deal with the molecules that remain. ODORGO Odor Eliminator Spray on the dry surface; Odor Eliminator Gel in small, enclosed spaces so it keeps working continuously.
5. Repeat. For an odor that has built up over years, one application is not enough; it takes several rounds.

Getting the order wrong is the most common mistake. Spraying while the source is still there, applying product to a wet surface, or trying to remove the odor without cleaning off the oily film limits the result from the start. The spray is water-based; you can use it on any surface that water does not harm. On water-sensitive fabrics and surfaces (unfinished or untreated wood, silk, leather, electronics, etc.), test on a small hidden area first.

Frequently Asked Questions

Does airing out really get rid of an odor?

It changes the air in the room; it does not remove molecules clinging to surfaces. Once the window closes, the surfaces keep releasing, so the odor returns. Airing out is a necessary step, but it is not enough on its own.

Why does an odor get stronger when it warms up?

Heat speeds up the molecule's move from the surface into the air. That is why heating, sunlight and a car that has been closed up make the odor more noticeable.

Why don't glass and tile smell?

Because they are non-porous, the odor molecule finds nowhere to cling. What holds the odor is the grout, the silicone and the porous surfaces around them.

Will painting get rid of the odor?

Paint applied before the oily residue is cleaned off covers the odor for a while; then it comes back from under the paint and from other surfaces. Clean the surface first, then paint.

How many times do I need to apply it?

For a fresh odor, one round is usually enough. Old cigarette odor or heavy pet odor takes several repeats; with each round, fewer molecules remain.

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