Are bad odors necessarily toxic?

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Hydrogen sulphide (H2S) is a very toxic gas giving off an obviously very unpleasant odor of rotten egg. Should we therefore conclude that there is a link between bad smells and dangerousness? Not necessarily, especially because some toxic substances smell good.

Harmless bad odors

In 2018, scientists made a list of the world’s worst smells. These include the durian (Asian fruit), the parasitic plant Rafflesia arnoldii or even Old Boulogne cheese. In short, nothing very dangerous. Many other bad smells are unbearable, such as that of a rotting body, a rotten egg or certain odors of gas or feet. In reality, odors are subject to a subjective perception specific to each individual.

While obviously some smells disgust everyone, some people enjoy smells that can be described as bad by the majority. In addition, the perception of a smell is also linked to emotions. In addition, a smell may remain good or become bad depending on its concentration. Let us quote for example the 1-p-Menthene-8-thiol, compound giving its scent to grapefruit. At low doses, it is pleasant, but becomes aggressive when the concentration increases.

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Case by case in terms of dangerousness

Can bad smells be dangerous? The answer is yes. The most telling example is none other than hydrogen sulfide (H2S). Fatal if inhaled, this gas causes respiratory tract irritation and eyes. This is also extremely flammable. According to Canadian Center for Occupational Health and Safety (CCOHS), this gas smells like rotten eggs. This disgusting odor in high concentrations can even numb the sense of smell. Other examples exist such as perchlorethylene, a solvent that dry cleaners use to clean fabrics. This volatile organic compound (VOC) gives off an odor resembling that of ether.

However, a bad smell should not be automatically associated to danger. You have to do it on a case-by-case basis for a very simple reason: there are also dangerous products that smell good! For example, hydrogen cyanide (HCN) smells of bitter almond. Benzene (C₆H₆) has a sweet, sweet odor that can be found especially around gasoline pumps. We can also mention the odors emanating from tubes of glue or markers that many appreciate despite their toxicity.

Finally, remember that methane (CH4) or carbon monoxide (CO) are gases totally odorless. And yet, they are among the gases most often involved in domestic accidents. However, it is precisely the absence of smell that makes them dangerous!

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