Smell is one of the five most important senses (sight, hearing, touch and taste), allowing us to perceive life in its entirety. The perception of smell is a very complex process including the excitation of specialised receptors located in the human nasal cavity, and signal transmission to the brain. Smells are caused by volatile chemical compounds, which can often be recognised even when present in low concentrations.
Odour plays an important role in our lives. It evokes emotions and memories, changes cognitive and physical abilities, and of course affects relationships between people. For this reason, the problem of odours has been preoccupying scientists and industrial developers for many years.
We have to consider the subjective perception when talking about pleasant and unpleasant odours. Acceptance of unpleasant odours can be determined by averaging the opinion of the population. The main source of malodours are sulfur and nitrogen containing molecules, such as allicin – garlic, felinine - cat urine, hydrogen sulfide - rotten eggs, ammonia – urine, indole and skatole – fecal, cadaverine and putrescine – rotting flesh, nicotine – tobacco and so on. In addition, there are other odorous substances that are responsible, for example for smell of sweat - isovaleric acid, rancid oil - butanoic acid, tobacco smoke - acetaldehyde etc. In everyday life the number of unpleasant odours originated from non-sulfur and nonnitrogen containing molecules is very limited.
The most common solution to ‘change’ unpleasant odours is the use of fragrances. Such mixtures release a pleasant scent and are able to cover unpleasant odours. This masking is not always effective and after dispersing the fragrance, unpleasant odour molecules will be predominant in the atmosphere again.
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