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Odour information


Odour does not receive as much attention as the other sense organs. This very undeserved, as odour is apllied more than we know. For instance, taste of a product is determined by its odour for ninety percent. Our tongue only has the ability to taste salts, acids, acrid and sweets. Unknowingly odour plays an important part in perception.
Odour is the determining factor for an attraction between the sexes. However, this happens unconsciously, as the odour cannot be detected. Contrary to what people may think even urine and sweaty smells have a positive effect on the attraction between the sexes, but only if humans can barely detect these odours. Urine and sweat contain hormones that may or may not cause a sexual attraction between two people. Because of this those kinds of odour are often added to perfumes. The MHC (Major Histocompatibility Complex) clearly influences the kind of smell that a woman finds attractive in a man. Mostly men that have an MHC that differs from a woman's MHC attract women. Claus Wedekind has researched this. He thinks it probably has something to do with reproduction, because children need to have a very and diverse immune system.

Each person has a different odour, just like each person has a different fingerprint. According to a recent theory a person's odour can be linked indirectly to a person's unique genes. The genes of the immune system determine the composition of bacteria on a person's skin. The bacteria decompose sebum from the sebaceous gland to fatty acids. Through this process each person receives a unique composition of fatty acids, which determines its odour characteristics.

Odours can do more than simply give people memories of images or sounds. This is because our nasal organ is in direct contact with the system where our memory and our emotions are centred. That is why odours are often connected to moods.
For example, when you have been experiencing a stench all day, your temper will be very bad, but when you arrive in a forest you often feel peaceful and calm. Because of these effects incense packages often have an inscription that tells you how the specific scent will affect your mood.
Contrary to humans, animals very widely use their sense of smell. For example, animals use odour to mark out their territory and to lure congeners of the opposite sexe. Animals will respond to this much more, because they use their sense of smell so often. When a male smells a female in heat, he will respond to this very passionately.
In odour industries people have tried to find the ultimate luring scent, but it has not been discovered yet.

Odours can be very unpleasant. The tip of a stuffed shower does not smell very pleasant and it does not work very positively on the senses. Another unpleasant odour is that which hangs around farms, which contain cows and pigs. To prevent the odours on a farm the air can be washed by means of an absorbent, which removes components that cause odour problems.

It is difficult to detect and describe an odour. Try to describe what your shampoo or your home smells like. People can often describe the smell of their shampoo, for instance sweet and peachy, but a description of the smell of their house is very hard.
Usually when you try to find ways to describe the smell you will see images and you will end up describing feelings instead of odours.

What is odour?

But what exactly is odour? This is a very tough question. Some substances have stronger odours than others, only small amounts have to be present to make someone detect them. For some substances it takes a long time before we can detect them.
If we want to be able to smell a substance it has to be gaseous, fatty or water-soluble. Our sensibility for odours differs for each substance.

Our sensibility for the odour of a substance is expressed as a threshold value. This is the concentration of a substance that can be detected by half of the people that are present.
- Chloroform is detected when 130 molecules are present in a million molecules of air.
- Chlorophenols can already be detected when 3 molecules are present in a hundred billion molecules of air.
Humans can differ up to a factor of a hundred thousand in their sensibility for a certain substance.

We are often warned for the effect of a product by its odour. For example, rotten food smells nasty and when toxic substances such as hydrogen sulphide are present you can smell it. Hydrogen sulphide smells like rotten eggs.

Commercially odour has not really been exploited yet. Sometimes it is used to influence buying behaviour of people, for example when we put down a bread oven in a super market. In some of the Japanese office buildings the air-conditioning blows fresh odours into the air, in the morning, in order to make people work more actively.

Odour nuisance

Odour nuisance is often defined as: the cumulative result of a repeating disturbance by odours, which is characterized by behavioural changes. The behavioural changes can manifest actively (complaining, close windows, go inside) or passively (signals in questionnaires through divergent answers).
Words such as cumulatively and repeatedly implicate that odour nuisance is not a momentous kind of nuisance; it is the nuisance that is caused by a certain exposure to odours over a longer period of time. The highest concentrations usually determine the extent of nuisance, which people will experience.

Odour nuisance can lead to both physical and mental effects (health effects and negative experiences). We have not been able to determine a direct relationship between the odour of substances and the toxicity of the substances, expressed as pathogenic effects. However, people have observed non-toxicological physiologic reactions by odours acting upon the central or peripheral nerve system.
From questionnaires and events we can determine that periods of odour nuisance often go together with headaches, nausea, sleep disturbances, a loss of appetite and stress.
Whether flora and fauna undergo influences from being in touch with human aromatic substances has not been specified yet.
What we do know is that economic effects can be caused by odour nuisance. The effects can be caused, for instance, by a decrease of productivity of employees (such as a decrease in concentration), a loss of costumers in commercial centres and a decrease in value of immovable property in areas that suffer from odour nuisance.

Odour definitions

Odour concentration
The number of odour units per unit of volume. The numeric value of the odour concentration, expressed in odour units ( E/ m3 ) equals the number of times that the air should be treated with odourless air to reach the odour threshold.

Odour threshold
The concentration of a gaseous substance, expressed in µg/m3, which will be discerned from odourless air by at least half of an odour panel. The odour threshold per definition has an odour concentration of 1 odour unit/ m3.

Odour standard
A standard for odour, expressed as a maximum concentration, which may not be crossed.

Serious odour nuisance
A degree of odour nuisance which exceeds the maximum admittable level for human health. Both health effects and personally experienced effects play a part here. In practise a level of odour nuisance is determined by questionnaires in which people can describe the degree of odour nuisance they have experienced.

Zero-effect level
This is the highest possible odour concentration in which people do not experience odour nuisance yet.

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