Why do we experience some things as ‘stench’ and others as ‘smell good’?

Answer

Dear Arthur,

Actually, you said it yourself: we experience certain things as stench or smell good; in other words, there is a certain subjective aspect to it. The brain translates a signal into a positive or negative appreciation. We have been trained to some extent through evolution to find certain things repulsive and other things attractive. In that sense, that is indeed ingrained in us and we are adapted to our environment. In fact, this appreciation for certain odors is also linked to certain chemical structures. For example, sulfur compounds and nitrogen compounds (= amines) are often formed during putrefaction and are therefore labeled as negative. The smell is then a warning not to eat it, if you do eat it you will get sick. On the other hand, pleasant smells such as floral or fruit smells are related to chemical compounds such as esters and they refer to potential food. This is pretty much the basis of the olfactory system, warning of an unhealthy substance or positive evaluation of something that may refer to food. Since the nose can “feel” the structure of chemical groups in compounds in this way, substances that look similar will have a similar smell. For example, we experience almost all esters as smelling good, even if that ester is completely synthetic and has never occurred in nature, but that has to do with the fact that an ester group is also present in the compound there. The same also applies to compounds that smell: all amines “smell to a greater or lesser extent.

Regards