Pet odour in an indoor space is carried by three compounds that behave very differently. Ammonia is produced from urine nitrogen and rises readily in a warm room. Hydrogen sulphide is a heavier, more localised compound associated with faecal degradation. Skatole is the compound that gives faecal material its distinctive note and is the one most products fail to address. Treating the three separately is more effective than treating “odour” as a single problem.
Product referenced in this article
Pet Deodoriser for Cats — application notes, specification table and document downloads for this range.
Ammonia: the compound that rises
Ammonia is what urine contributes, and it is the compound most often described as the sharp “animal” note in a room. It forms when urine nitrogen is broken down, and it is favoured by warmth, still air and a high pH. Three practical consequences follow. Ammonia is light enough to mix through the air of a room, so a source in one corner affects the whole space. It rises, so a low source such as a litter tray or a bedding box affects the breathing zone of anyone sitting down. And it is strongly absorbed by textiles — carpets, curtains, upholstery and bedding — where it accumulates and is re-released for months after the original source is removed.
That last point is the one that changes how a control programme has to be run. Ammonia removal from the air alone produces a result that fades within days, because the source and the reservoir are both still present. Effective control means treating the waste where it is produced, and the textile reservoir needs separate attention once the source is under control.
Hydrogen sulphide: the heavy one
Hydrogen sulphide is produced by anaerobic breakdown of sulphur-containing material, which in a pet context means faecal matter sitting in conditions without oxygen. It is heavier than air, so it does not distribute through the room the way ammonia does; it accumulates in the container and in the immediate airspace above it. It is also the compound most associated with the perception of a sewage or rotten-egg note, and it is detectable at concentrations far below the levels at which it becomes hazardous.
Because it is heavy and localised, a room-level deodoriser is the wrong tool for it. Control has to happen at the source, in the container, with enough frequency to prevent anaerobic conditions from establishing. Air treatment in the room can mask the note but does nothing about the material producing it.
Skatole: the one most products miss
Skatole is the compound that carries the distinctive fecal odour, and it is the usual reason a room continues to smell of animals after the waste has been removed and the surfaces cleaned. It forms in the hindgut from tryptophan breakdown and is present in faecal material from the moment it is produced. Being a low-volatility, persistent compound, it stays in textiles and porous surfaces long after the visible material is gone, and it has a low odour threshold.
This is the practical reason why a room can keep smelling after a thorough clean. Standard cleaning removes the material that is still producing skatole, but skatole already bound into fibres and fabrics is not removed by it, and is slowly re-released. Any control programme that has not addressed that reservoir will be working against a source that is not the one you can see.
Matching the treatment to the compound
Once the three are separated, the control routes are straightforward. For ammonia, the priority is frequent removal of urine-contaminated material, together with absorbent coverage under litter or bedding. Ammonia is a nitrogen problem, and it responds to removal rate more than to any product. Enzyme-based products that break down the protein residues releasing ammonia are useful here, because they address the source rather than the air.
For hydrogen sulphide, the control point is the container: keep the material aerated and non-anaerobic, and do not let the cleaning interval stretch. Absorbents that keep the surface drier are directly useful because anaerobic onset is a function of moisture and stagnation.
For skatole, the control point is the textile reservoir. Enzyme formulations selected for the relevant substrate class are the standard answer, together with washing or professional cleaning of the affected textiles. If a room has a persistent fecal note that survives cleaning, the source is in the fabric, and any product applied to the air is buying time at best.
We describe all of our products in this area as reducing odour and improving the biological handling of the waste. We do not describe them as sterilants, and we do not publish sterilisation or disinfection efficacy figures, because the mechanism of a biological or enzyme deodoriser does not support that claim. A buyer who needs a validated kill rate is asking for a different product category, and it is worth saying so plainly at the specification stage rather than after delivery.
Why the smell often returns after a clean
Almost always because of the textile reservoir, and occasionally because the cleaning interval is being stretched without anyone deciding to change it. If a room is cleaned and the note returns within a few days, the likely sequence is that the material producing skatole was removed from its container but not from the surrounding fabric, and the fabric has been re-emitting the whole time. A deodoriser applied to the air will appear to work for a day or two and then fail, and the natural conclusion — that the product is weak — is the wrong one.
The useful check is to clean the textile reservoir, not the room. Wash the bedding, clean the upholstery and curtains, and then judge the deodoriser on whether the note stays away. If it does, the product was adequate and the programme was not. If it does not, the problem is a source that is still producing odour, and it is worth finding where that is before specifying more product.
Frequently asked questions
- What causes the smell in a room with a cat?
- Three compounds do most of the work. Ammonia comes from urine nitrogen and rises into the air of the room, where it is absorbed by textiles. Hydrogen sulphide comes from faecal degradation, is heavier than air and stays concentrated near its source. Skatole is the faecal note, and because it is a persistent low-volatility compound it remains in fabrics and is re-released long after the material producing it is gone.
- Why does the odour come back a few days after cleaning?
- Usually because of what is called the textile reservoir. Cleaning removes the material that is still producing skatole, but skatole already bound into carpets, curtains, upholstery and bedding is not removed by surface cleaning and is slowly re-released. Cleaning the affected textiles is what removes the source, after which deodorising products can be judged properly.
- Is ammonia the main cause of pet odour in a room?
- It is the compound that travels furthest, because it is light enough to mix through the air and is absorbed into textiles. But it is rarely the only one, and treating only the ammonia commonly leaves a faecal note behind. A programme that works on the three compounds separately is more effective than one that treats odour as a single problem.
- Does a biological deodoriser kill the bacteria causing pet odour?
- No, and we do not claim that it does. Biological and enzyme deodorisers reduce odour and improve the biological handling of the waste, by competing with the organisms that produce the strongest odours and by breaking down the odour-forming compounds themselves. They are not sterilants. If you need a validated kill rate, that is a different product category and should be specified as such.