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Smell ControlA variety of products and household remedies are available to combat odours in the home – with varying degrees of success. Learn more about the effectiveness of different methods and odour-control products.
Most unpleasant odours occur when microorganisms decompose and break down organic material (especially substances containing proteins). Our sense of smell is very sensitive to many of the resulting chemical compounds and thus does a good job of protecting us against food poisoning.
However, not all substances smell equally unpleasant to all animals.
Certain messenger substances found in animal excreta (cat urine, dog excrement, etc.) smell repulsive to us, but are extremely interesting to certain animals.
We also find the stench of faeces or rotting meat extremely disgusting. For a blowfly or common green bottle fly, however, these substances probably smell like freshly grilled chicken and attract them from far away. For this reason, some plants also produce attractants for insects that smell like carrion, rotten fish or faeces. These serve to aid their reproduction, or in the case of carnivorous plants, to provide nutrition.
Human beings generally find the lingering smell of a piece of old fish or rotting meat extremely repulsive and even nauseating.
In this case, the unpleasant aroma is caused by the ptomaine 1.5-diaminopentane or cadaverine and putrescine, chemical variants (amines) of ammonia (NH3) which are produced by the decomposition of the amino acid lysine. Our olfactory centre can detect these pungent aromas even in very low concentrations and associates them with the notion of „inedible and toxic“.
Another substance responsible for unpleasant odours in the home is skatole, which is also formed via microbial decay of amino acids. Skatole is responsible for the distinctive smell of excrement or manure. Recently used toilets, nappy bins and cat litter boxes are frequent sources of such odours. In contrast to the ptomaines, skatole is much more volatile, which means that „biological odour control“ is far easier by means of simple ventilation. The odour threshold of skatole is approximately 0.0005g (about 1/10 of a grain of sand) per cubic metre of air.
Hydrogen sulphide or dihydrogen sulphite H2S is another notorious chemical when it comes to odour control. This gas, which is highly toxic in significant concentrations and has an intense odour of rotten eggs, is also formed during biological decay processes. In the household, hydrogen sulphide is most commonly found in rotting siphons and stinking water drains – especially those regularly used for disposal of organic solids such as food waste. This inconspicuous process results in sludge that produces intense (and sometimes puzzling) odours that smell like rotten eggs and rotten fish. Some digestive processes also produce very small amounts of hydrogen sulphide. For example, when the family dog suffers another bout of flatulence – bringing tears to your eyes and making the kids run screaming from the room – it’s safe to say that hydrogen sulphide is (partly) to blame.
Another „usual suspect“ in terms of bad odours – and a sales-driver for many anti-odour products – is butyric acid.
Butyric acid or butanoic acid is a simple fatty acid that has an intense odour of vomit, cheese and sour milk. It is responsible for the smell of foot sweat and cheese rind. Occasionally it is misused in so-called butyric acid attacks in order to cause maximum damage to an opponent without seriously damaging their infrastructure or health. The worst thing about butyric acid is its ability to create an extremely intense, long-lasting stink.
Last but not least, we come to ammonia
Ammonia is formed during the decomposition of urine and liquid manure. Although only toxic in fairly high doses, the odour threshold of ammonia is very low. Its pungent smell is quite common in toilets that are neither used nor cleaned properly. When cracks and mortar joints are soaked with urine, they begin to smell despite regular cleaning and disinfection.
There are essentially five different methods of odour control:
The idea here is to mask and cover up the bad smell with a pleasant-smelling substance. Coffee powder, peppermint sweets, toothpaste, tea bags, Vicks Vapo Rub, perfume, etc. are placed in areas affected by an unpleasant odour. However, since the odour source itself is not affected, this method does not usually result in long-term success.
In this method, the goal is to break down unpleasant odours by means of oxidising substances such as ozone, hydroxyl radicals or singlet oxygen. While this method is sometimes fairly successful, it has two distinct drawbacks. Firstly, ozone generators should only be operated by professionals, otherwise there is a risk of serious damage to health.
Also, these devices will only tackle odours that are present in the air. In the case of infiltrated liquids, e.g. from a decomposing corpse in an apartment, the odour source itself is not affected. In addition, ozone damages plastics and many other materials.
Air purifiers equipped with ionisers and activated carbon filters are able to absorb many bad odours from the air. However, the odour sources themselves are not affected and these appliances must run continuously in order to be effective.
Via this approach the odour molecules are bound and neutralised by chemical substances such as zinc ricinoleate. Zinc ricinoleate is a non-toxic substance that is used in many detergents, fabric softeners and personal care products. It is highly effective against odour emissions of an organic nature, such as the odour sources described above. However, chemical odour neutralisers are ineffective against „chemical“ odours such as solvents, smoke/nicotine, soot, diesel, exhaust fumes, etc.
The most sustainable approach to odour control involves eliminating the odour’s source. Digested sludge in siphons, faulty fermentation in septic tanks or liquids seeping onto surfaces, such as urine, liquid dripping from bin bags, milk, etc. are decomposed with the help of enzymes and/or probiotic bacteria (so-called „effective microorganisms„). This is one of the most effective and long-lasting methods of odour control, however it requires some patience. Removal of the odour source takes more than a few seconds – in some cases, the process can last for hours or even days.
