We all know instinctively what good or bad odors are, but why is it so? What are the mechanics behind odor and its sources?
Odors are signals that guide our behavior, attracting us towards life and repelling from death and decay.
It is like a map drawn in thin air that helped our ancestors to survive through all odds and to make the right choices for their survival.
Today odours are still signals, as they build a very complex symbology in various areas of our life.
There are several aspects relating to odor which involve all our activities, from sport to social relationships, so it is not strange that this problem is being targeted in many different ways since many years.
Anatomy of odor
Technically speaking, odor is made of complex chemicals which are released in the atmosphere as a product of chemical or physical modifications. We are not going here into chemistry or physics, there are specialists who can do that very well. Examples of this are phenomena like fire or evaporation, the common point is that all these release particles in the atmosphere.
So what is the difference between good and bad odor? Actually none.
The difference is made in the evolution of our nervous system, which learned to associate odours related to decay, sickness and death to a certain type of response, and those related to life, reproduction and food to another type. This is all there is to it, there is no difference between a good and a bad odor, other than its meaning for our survival as organisms. The pattern of signals from our sensors, reacting with our experience and education, gives us a full range of responses, which can be of pleasure or disgust.
Odor perception is a primary evolutionary sense. The sense of smell can induce pleasure or subconsciously warn of danger, which may, for example, help to locate mates, find food, or detect predators. Humans have an unusually good sense of smell considering they have only 350 functional olfactory receptor genes compared to the 1,300 found in mice, for example. This is despite an apparent evolutionary decline in the sense of smell. The human sense of smell is comparable with many animals, able to distinguish between a diverse range of odors. Studies have reported that humans can distinguish in the region of one trillion unique aromas.
For most untrained individuals, the act of smelling acquires little information concerning the specific ingredients of an odor. Their smell perception primarily offers information that elicits an emotional response. Experienced individuals, however, such as flavorists and perfumers, can identify discrete chemicals in complex mixtures using only the sense of smell.
Sources of odor
We are used to look at macroscopic causes when it comes to odor, with the purpose of making simple choices between what is good and what is not.
But the sources of odours are basically of two types: organic and chemical. Organics include mostly bacteria and some viruses, including the response of other organisms to these, while chemical is mainly solvents and other volatile substances. Organic chemicals also exist, derived from fossile oil and other such products.
When we look at, or rather smell, food, dumpsters, bodies, perfumes, paint, or any other substance, we are inhaling particles which react with specific sensors in our nose. So it is much more important to distinguish between harmful and harmless odors rather than pleasant and disgusting ones.
A bit of biology
The perception of odors, or sense of smell, is mediated by the olfactory nerve. The olfactory receptor (OR) cells are neurons present in the olfactory epithelium, which is a small patch of tissue at the back of the nasal cavity. There are millions of olfactory receptor neurons that act as sensory signaling cells. Each neuron has cilia in direct contact with the air. Odorous molecules bind to receptor proteins extending from cilia and act as a chemical stimulus, initiating electric signals that travel along the olfactory nerve's axons to the brain. When an electrical signal reaches a threshold, the neuron fires, which sends a signal traveling along the axon to the olfactory bulb, a part of the limbic system of the brain.
Interpretation of the smell begins there, relating the smell to past experiences and in relation to the substance(s) inhaled. The olfactory bulb acts as a relay station connecting the nose to the olfactory cortex in the brain. Olfactory information is further processed and forwarded to the central nervous system, which controls emotions and behavior as well as basic thought processes. Odor sensation usually depends on the concentration (number of molecules) available to the olfactory receptors. A single odorant is usually recognized by many receptors. Different odorants are recognized by combinations of receptors.
The patterns of neuron signals help to identify the smell. The olfactory system does not interpret a single compound, but instead the whole odorous mix. This does not correspond to the concentration or intensity of any single constituent. Most odors consist of organic compounds, although some simple compounds not containing carbon, such as hydrogen sulfide and ammonia, are also odorants. The perception of an odor effect is a two-step process. First, there is the physiological part. This is the detection of stimuli by receptors in the nose. The stimuli are recognized by the region of the human brain which handles olfaction. Because of this, an objective and analytical measure of odor is impossible. While odor feelings are personal perceptions, individual reactions are usually related. They relate to things such as gender, age, state of health, and personal history.
Smell acuity by age and sex
The ability to identify odor varies among people and decreases with age. Studies show there are sex differences in odor discrimination, and women usually outperform men.
Pregnant women have increased smell sensitivity, sometimes resulting in abnormal taste and smell perceptions, leading to food cravings or aversions. The ability to taste also decreases with age as the sense of smell tends to dominate the sense of taste. Chronic smell problems are reported in small numbers for those in their mid-twenties, with numbers increasing steadily, with overall sensitivity beginning to decline in the second decade of life, and then deteriorating appreciably as age increases, especially once over 70 years of age.
Habituation or adaptation
Odors that a person is used to, such as their own body odor, are less noticeable than uncommon odors. This is due to habituation. After continuous odor exposure, the sense of smell is fatigued, but recovers if the stimulus is removed for a time. Odors can change due to environmental conditions: for example, odors tend to be more distinguishable in cool dry air.
Habituation affects the ability to distinguish odors after continuous exposure. The sensitivity and ability to discriminate odors diminishes with exposure, and the brain tends to ignore continuous stimulus and focus on differences and changes in a particular sensation. When odorants are mixed, a habitual odorant is blocked. This depends on the strength of the odorants in the mixture, which can change the perception and processing of an odor. This process helps classify similar odors as well as adjust sensitivity to differences in complex stimuli.
Odor sources treatment
Being our society basically chemical, when it comes to odor treatment, this is done by exterminating its causes by means of chemical products. This is what we see on the market nowadays: a full range of remedies which remove odor without addressing the underlying issues. All in all, this is a form of pollution that has also the characteristic of being very near to our body, with different side effects on the long run due to over exposure to chemical agents, or at least a reduced sensitivity to odor.
What the chemicals do is twofold: kill all living sources of odor while emitting fragrance particles to cover any residual odor particle. There are many outpoints in this approach: the constant sanitation of surfaces and areas, including our skin, leads to the selection of resistant micro-organisms, which are more difficult to defeat. Moreover, the quantity of complex chemicals introduced is not absorbed in the environment and it produces global effects, as the ozone hole or greenhouse effects. We must learn that there is a limit to the quantity of chemicals we can introduce in air and water.
As the world is anyhow literally covered with bacteria and other organisms, a biological approach would prove more successful on the long run. Instead of fighting all life with chemical poison, we can learn to favor useful life forms to help reduce and eliminate harmful ones. This is what we do whenever we consume probiotics for our bowel's health. We somehow recognize there is an unbalance in the life forms which live in our digestive system and we balance it by providing helpful bacteria which will colonize it and remove harmful ones.
The insertion in the environment of selected types of bacteria, which produce non smelling subproducts, helps these life forms to colonize the environment praying on their competitors, until all foul smelling organisms are removed. This solution is also very stable, because it doesn't leave an aseptic space where resistent life forms can multipiicate without any barrier, but a well populated environment with favorable life forms.
As we live after all in a western society and we want an immediate action over smell, rather than a lomg term solution, there are three effective ways to remove odor withiout the use of chemicals. The first is to demolish odor particles with specific enzymes which divide them into simpler compounds, the second is to combine odor particles with enzymes resulting in a different compound without odor and the third is to combine them with heavy particles that fall to the ground, removing odor particles from air. The type of strategy depends on the type of odor, and all three are present in our solutions of the deo product line.
So, how do we know when odor is gone, ie. we used enough product? To make sure the odor particles are actually gone, we add a tracing fragrance to our odor treatment products. The reason is simple: as long as you can smell the fragrance, our deo products are treating other odors which are present in the environment. When the fragrance is completely gone, that means there are no other odor particles in the air and our product is combining solely with it.