Product Code Database
An odor (American English) or odour (Commonwealth English; see spelling differences) is a smell or a scent caused by one or more volatilized chemical compounds generally found in low concentrations that humans and many animals can perceive via their olfactory system. While smell can refer to pleasant and unpleasant odors, the terms scent, aroma, and fragrance are usually reserved for pleasant-smelling odors and are frequently used in the food and cosmetic industry to describe or to refer to .
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 (CNS), 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 Aroma compound 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.Spengler, p. 492
Most odors consist of , 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.
Pregnant women have increased smell sensitivity, sometimes resulting in abnormal taste and smell perceptions, leading to 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.
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.
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.
The measurement of odor concentration is the most widespread method to quantify odors. It is standardized in CEN EN 13725:2003.. sipe-rtd.info The method is based on dilution of an odor sample to the odor threshold. The numerical value of the odor concentration is equal to the dilution factor that is necessary to reach the odor threshold. Its unit is the "European Odour Unit", OUE. Therefore, the odor concentration at the odor threshold is 1 OUE by definition.
In comparing the odor emitted from each port, the panelists are asked to report if they can detect a difference between the ports. The gas-diluting ratio is then decreased by a factor of 1.4 or two (i.e., the concentration is increased accordingly). The panelists are asked to repeat the test. This continues until the panelists respond with certainty and correctly twice in a row. These responses are used to calculate the concentration of the odor in terms of European odor units (OUE/m3, where 1 OUE/m3≡40 ppb/v n-butanol).
Humans can discriminate between two odorants that differ in concentration by as little as 7%. A human's odor detection threshold is variable. Repeated exposure to an odorant leads to enhanced olfactory sensitivity and decreased detection thresholds for a number of different odorants. It was found in a study that humans who were unable to detect the odor of androstenone developed the ability to detect it after repeated exposure. People who cannot smell are said to be anosmia.
There are a number of issues which have to be overcome with sampling, these include:
Issues such as temperature and humidity are best overcome using either pre-dilution or dynamic dilution techniques.
When measuring odor, there is a difference between and measurements. Emission measurement can be taken by olfactometry using an olfactometer to dilute the odor sample. Olfactometry is rarely used for immission measurement because of low odor concentrations involved. The same measuring principles are used, but the judgment of the air-assay happens without diluting the samples.
Odor measurement is essential for odor regulation and control. An odor emission often consists of a complex mixture of many odorous compounds. Analytical monitoring of individual chemical compounds present in such an odor is usually not practical. As a result, odor sensory methods, instead of instrumental methods, are normally used to measure such odor. Odor sensory methods are available to monitor odor both from source emissions and in the ambient air. These two contexts require different approaches for measuring odor. The collection of odor samples is more easily accomplished for a source emission than for odor in the ambient air.
Field measurement with portable Olfactometer can seem more effective, but olfactometer use is not regulated in Europe, while it is popular in the U.S. and Canada, where several states set limits at the receptor sites or along the perimeter of odor-emitting plants, expressed in units of dilution-to-threshold (D/T).
The perceived strength of an odor is measured alongside its concentration and can be mathematically modeled using the Weber-Fechner law: I = a × log(c) + b, where:
Odor intensity can be expressed using an odor intensity scale, which is a verbal description of an odor sensation to which a numerical value is assigned.
Odor intensity can be divided into the following categories according to intensity:
Odor intensity is determined in a laboratory by specialists who have been trained to accurately define intensity.
The character of an odor is a critical element in assessing an odor. This property is the ability to distinguish different odors and is only descriptive. First, a basic description is used—such as sweet, pungent, acrid, fragrant, warm, dry, or sour. The odor is then referenced to a source such as sewage or apple which can then be followed by a reference to a specific chemical such as acids or gasoline.
Most commonly, a set of standard descriptors is used, which may range from "fragrant" to "sewer odor". Although the method is fairly simplistic, it is important for the FIDOL factors to be understood by the person rating the smell. This method is most commonly used to define the character of an odor which can then be compared to other odors. It is common for olfactometry laboratories to report character as an additional factor post sample-analysis.
Though the concept of primary odors is not universally accepted.
The most commonly used direct methods include the flux chamber and such as the one at the University of New South Wales (UNSW). UNSW wind tunnel dimensions. Odour.unsw.edu.au There are many other available techniques, and consideration should be given to a number of factors before selecting a suitable method.
A source which has implications for this method are sources, such as bark bed , that have a vertical velocity component. For such sources, consideration must be given as to the most appropriate method. A commonly used technique is to measure the odor concentration at the emitting surface, and combine this with the volumetric flow rate of air entering the biofilter to produce an emission rate.
Many methods are used, but all make use of the same inputs which include surface roughness, upwind and downwind concentrations, stability class (or other similar factor), wind speed, and wind direction.
The perception of irritation from odor sensation is hard to investigate because exposure to a volatile chemical elicits a different response based on sensory and physiological signals, and interpretation of these signals is influenced by experience, expectations, personality, or situational factors. Volatile organic compounds (VOCs) may have higher concentrations in confined indoor environments, due to restricted infiltration of fresh air, as compared to the outdoor environment, leading to greater potential for toxic health exposures from a variety of chemical compounds. Health effects of odor are traced to the sensation of an odor or the odorant itself. Health effects and symptoms vary—including eye, nose, or throat irritation, cough, chest tightness, drowsiness, and mood change—all of which decrease as an odor ceases. Odors may also trigger illnesses such as asthma, depression, stress-induced illness, or hypersensitivity. The ability to perform tasks may decrease, and other social/behavioral changes may occur.
Occupants should expect remediation from disturbing and unexpected odors that disturb concentration, diminish productivity, evoke symptoms, and generally increase the dislike for a particular environment. It is important to set occupational exposure limits (OELs) to ensure the health and safety of workers, as well as comfort, because exposure to chemicals can elicit physiological and biochemical changes in the upper respiratory system. Standards are hard to set when exposures are not reported and can also be hard to measure. Workforce populations vary in terms of discomfort from odors because of exposure history or habituation, and they may not realize possible risks of exposure to chemicals that produce specific odors.
Odor molecules transmit messages to the limbic system, the area of the brain that governs emotional responses. Some believe that these messages have the power to alter moods, evoke distant memories, raise spirits, and boost self-confidence. This belief has led to "aromatherapy", wherein fragrances are claimed to cure a wide range of psychological and physical problems. Aromatherapy claims that fragrances can positively affect sleep, stress, alertness, social interaction, and general feelings of well-being. Evidence for the effectiveness of aromatherapy is mostly anecdotal and controlled science studies to substantiate its claims are lacking.
Some people are allergic to the fragrances found in perfume, scented shampoo, scented deodorant, or similar products. Reactions, as with other chemical allergies, can range from slight headaches to anaphylactic shock, which can result in death.
Unpleasant odors play various roles in nature, often to warn of danger, though this may not be known to the subject who smells it. The natural gas industry uses odor to enable consumers to identify leaks. Natural gas in its native state is colorless and almost odorless. To help users detect , an odorizer with the scent of rotten eggs, tert-Butylthiol (t-butyl mercaptan), is added. Sometimes a related compound, thiophane, may be used in the mixture.
An odor that is viewed as unpleasant by some people or cultures can be viewed as attractive by others where it is more familiar or has a better reputation. It is commonly thought that those exuding an unpleasant body odor are unattractive to others. But studies have shown that a person who is exposed to a particular unpleasant odor can be attracted to others who have been exposed to the same unpleasant odor. (1991). 9780275941116, Praeger. ISBN 9780275941116 This includes odors associated with pollution.
What causes a substance to smell unpleasant may be different from what one perceives. For example, perspiration is often viewed as having an unpleasant odor, but it is odorless. It is bacteria in the perspiration that causes the odor.
Unpleasant odors can arise from specific industrial processes, adversely affecting workers and even residents downwind of the source. The most common sources of industrial odor arise from sewage treatment plants, Refining, animal rendering factories, and industries processing chemicals (such as sulfur) which have odorous characteristics. Sometimes industrial odor sources are the subject of community controversy and scientific analysis.
Body odor is present both in animals and humans and its intensity can be influenced by many factors (behavioral patterns, survival strategies). Body odor has a strong genetic basis both in animals and humans, but it can be also strongly influenced by various diseases and psychological conditions.
The study of odors is complicated by the complex chemistry taking place at the moment of a smell sensation. For example, iron-containing metallic objects are perceived to have a distinctive odor when touched, although iron's vapor pressure is negligible. According to a 2006 study, this smell is the result of (for example, nonanal) and : 1-octen-3-one) released from the human skin on contact with ferrous ions that are formed in the sweat-mediated corrosion of iron. The same chemicals are also associated with the smell of blood, as ferrous iron in blood on skin produces the same reaction.
Human influence interpersonal relationships and are involved in adaptive behaviors, such as parental attachment in infants or partner choice in adults. "Mothers can discriminate the odor of their own child, and infants recognize and prefer the body odor of their mother over that of another woman. This maternal odor appears to guide infants toward the breast and to have a calming effect." Body odor is involved in the development of infant–mother attachment and is essential to a child's social and emotional development and evokes feelings of security. Reassurance created by familiar parental body odors may contribute significantly to the attachment process. Human body odors can also affect mate choice. Fragrances are commonly used to raise sexual attractiveness and induce sexual arousal. Researchers found that people choose perfume that interacts well with their body odor.
Body odor is a sensory cue critical for mate selection in humans because it is a signal of immunological health. Women prefer men with major histocompatibility complex (MHC) genotypes and odor different from themselves especially during ovulation. Different MHC alleles are favorable because different allele combinations would maximize disease protection and minimize recessive mutations in offspring. Biologically females tend to select mates "who are most likely to secure offspring survival and thus increase the likelihood that her genetic contribution will be reproductively viable."
Studies have suggested that people might be using odor cues associated with the immune system to select mates. Using a brain-imaging technique, Swedish researchers have shown that homosexuality and heterosexuality males' brains respond in different ways to two odors that may be involved in sexual arousal, and that the gay men respond in the same way as straight women, though it could not be determined whether this was cause or effect. The study was expanded to include lesbian women; the results were consistent with previous findings that lesbian women were not as responsive to male-identified odors, while their response to female cues was similar to that of straight males. According to the researchers, this research suggests a possible role for human pheromones in the biological basis of sexual orientation.Wade, Nicholas (May 9, 2005) "Gay Men are found to have Different Scent of Attraction". NY Times
An odor can cue recall of a distant memory. Most memories that pertain to odor come from the first decade of life, compared to verbal and visual memories which usually come from the 10th to 30th years of life. Odor-evoked memories are more emotional, associated with stronger feelings of being brought back in time, and have been thought of less often as compared to memories evoked by other cues.
If ingredients are listed on a product, the term "fragrance" can be used in a general sense.
In 2001, a study found that the major histocompatibility complex (MHC) (a polymorphic set of genes which is important for immune-function in humans) is correlated with the ingredients found in perfume. This suggests that humans do, in fact, choose perfumes that complement or enhance their natural scents (their pheromones). This evidence offers support for the hypothesis that perfume is chosen by individuals to advertise their physical health. Research suggests that this advertisement of good health will, in fact, enhance females' attractiveness to the opposite sex as health markers have been shown to do. While strong evidence has been found to support the hypothesis that wearing perfume enhances females' attractiveness to males, little research has been done into the effect of fragrance on males' attractiveness to females. Considerably more research has covered the effect of males' natural odor and females' ratings of attractiveness. Many studies found that odor predicted attractiveness when female raters were not on any form of contraceptive pill. For those who were, there was no relation between attractiveness and body odor.
A person's odor can increase or decrease ratings of attractiveness because the olfactory receptors in the brain are directly linked with the limbic system, the part of the brain that is thought to be most involved with emotion. This link is important, because if an individual associates positive affect (elicited by pheromones), with a potential mate, their liking for, and attraction to, that potential mate will be increased. Although not a typically evolutionary hypothesis, this hypothesis is one that acknowledges how humans have adapted their mating strategies to modern-day societal norms.
Body odor can provide MHC information. Although less is known about how odor is influenced by MHC genes, possible explanations have been that Microbiota or volatile acids are affected by the gene, which can be detected in body odor. Female mice and humans have both shown odor preferences for males with MHC-dissimilarity.
There are several scents that reflect good genetic quality that females prefer during the most fertile phase of their cycles. Women prefer the scent of symmetrical men more during the fertile phases of their menstrual cycle than during their infertile phases, with estrogen positively predicting women's preferences for the scent of symmetry. Women's preferences for masculine faces is greatest when their fertility is at its highest, and so is the preference for attractive faces. Other scents found to be preferred by women in the most fertile phase of their cycle are the scent for developmental stability.
If women are taking a contraceptive pill the changes in mate scent preferences over the menstrual cycle are not expressed. If odor plays a role in human mate choice then the contraceptive pill could disrupt disassortative mate preferences. Those taking a contraceptive pill show no significant preference for the scent of either symmetrical or asymmetrical men, whereas normally cycling women prefer the scent of shirts worn by symmetrical men. Males' preferences for women's scent may also change if the woman is taking oral contraceptives. When women take a contraceptive pill, this has been found to demolish the cycle attractiveness of odors that men find attractive in normally ovulating women. Therefore, a contraceptive pill affects both women's preferences for scent and also affects their own scents, making their scent less attractive to males than the scent of normally cycling women.
Use in design
The sense of smell is not overlooked as a way of marketing products. The deliberate and controlled application of scent is used by designers, scientists, artists, perfumers, architects, and chefs. Some applications of scents in environments are in casinos, hotels, private clubs, and new automobiles. For example, "technicians at New York City’s Sloan-Kettering Cancer Center disperse vanilla-scented oil into the air to help patients cope with the claustrophobic effects of MRI testing. Scents are used at the Chicago Board of Trade to lower the decibel level on the trading floor."
Scent preferences
Effect of perfume on sexual attractiveness
Both men and women use perfume to boost their sexual attractiveness to members of the opposite, or same, sex. When people find that a particular perfume or aftershave is perceived positively, they may be hard-pressed to change it. Olfactory communication is natural in humans. Without perfume or aftershave, humans unconsciously detect people's natural scents: in the form of pheromones. Pheromones are usually detected unconsciously, and it is believed that they have an important influence on human's social and sexual behaviour. There are a number of hypotheses concerning why humans wear perfume or aftershave, and whether it amplifies or reduces their natural scents.
Major histocompatibility complex (MHC) and body odor preferences
Major histocompatibility complex (MHC) is a genotype found in vertebrates, including humans. MHC is thought to contribute to mate choice in animals and humans. In sexual selection, females opt for mates with an MHC which differs from their own, optimising genes for their offspring. The "heterozygote advantage" and "Red Queen" explanations for these findings fall under the "pathogen hypothesis". Due to differences in MHC alleles' resistance to pathogens, a preference for mates with a dissimilar MHC composition has been argued to act as a mechanism to avoid infectious diseases. According to the -advantage hypothesis, diversity within the MHC genotype is beneficial for the immune system due to a greater range of antigens available to the host. Therefore, the hypothesis proposes that MHC heterozygotes will be superior to MHC in fighting off pathogens. Experimental research has shown mixed findings for this idea. The "Red Queen" or "rare-allele" hypothesis suggests that diversity in the MHC gene provides a moving target for pathogens, making it more difficult for them to adapt to MHC genotypes in the host. Another hypothesis suggests that preferences for MHC-dissimilar mates could serve to avoid inbreeding.
(2025). 9780198568308, Oxford University Press. ISBN 9780198568308 Research has shown that women prefer the scent of men with dissimilar MHC genes. In a study, women rated the scent of T-shirts, worn over two nights by men, as more pleasant when smelling those of MHC-dissimilar men. It has also been found that women were reminded more of current or prior partners when smelling odors from men whose MHC was dissimilar to their own. A study of married couples found that MHC haplotypes differed between spouses more than chance would dictate. Taking oral contraceptives has been found to reverse the MHC-dissimilarity odor preference.
Women's scent preferences and the menstrual cycle
Women's preferences for body odor change with their . The ovulatory-shift hypothesis argues that women experience elevated immediate sexual attraction, relative to low-fertile days of the cycle, to men with characteristics that reflect good genetic quality. As certain body odors can reflect good genetic quality, woman are more likely to prefer these scents when they are fertile, as this is when they are most likely to produce offspring with any potential mates, with conception-risk being related to a preference for the scent of male symmetry. Men also prefer the scent of women at their fertile cycle points.
See also
Further reading
|
|
