Odor

, Museo del Prado 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 floral scents or to refer to perfumes.

, Museo del Prado ]] 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 floral scents or to refer to perfumes. 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: I represents the perceived psychological intensity at a given dilution step on the butanol scale, a is the Weber-Fechner coefficient, C is the chemical concentration, and b is the intercept constant (0.5 by definition). 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: 0 – no odor 1 – very weak (odor threshold) 2 – weak 3 – distinct 4 – strong 5 – very strong 6 – intolerable Odor intensity is determined in a laboratory by specialists who have been trained to accurately define intensity. == Types== Some odors are sought after, such as from perfumes and flowers, some of which command high prices. Whole industries have developed around products that remove or mask unpleasant odors, such as deodorant. 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 scientific 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 leaks, 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. 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, refineries, 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. ===Study=== The study of odors is a growing field but is a complex and difficult one. The human olfactory system can detect many thousands of scents based on only minute airborne concentrations of a chemical. The sense of smell of many animals is far superior. Some fragrant flowers give off odor plumes that move downwind and are detectable by bees more than a kilometer away. 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 aldehydes (for example, nonanal) and ketones: oct-1-en-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. ===Pheromones=== Pheromones are odors that are used for communication, and are sometimes called "airborne hormones". A female moth may release a pheromone that can entice a male moth that is several kilometers downwind. Honeybee queens constantly release pheromones that regulate the activity of the hive. Worker bees can release such smells to call other bees into an appropriate cavity when a swarm moves into new quarters, or to "sound" an alarm when the hive is threatened. ===Advanced technology=== Most artificial or electronic nose instruments work by combining output from an array of non-specific chemical sensors to produce a fingerprint of whatever volatile chemicals in the local environment. Most electronic noses need to be "trained" to recognize chemicals of interest before it can be used. Many current electronic-nose instruments suffer from problems with reproducibility subject to varying ambient temperature and humidity. An example of this type of technology is the colorimetric sensor array, which visualizes odor through color change and creates a "picture" of it. ==Behavioral cues== Odor perception is a complex process involving the central nervous system and can evoke psychological and physiological responses. Because the olfactory signal terminates in or near the amygdala, odors are strongly linked to memories and can evoke emotions. The amygdala participates in the hedonic or emotional processing of olfactory stimuli. Odors can disturb our concentration, diminish productivity, evoke symptoms, and in general increase a dislike for an environment. Odors can impact the liking for a person, place, food, or product as a form of conditioning. Memories recalled by odors are significantly more emotional and evocative than those recalled by the same cue presented visually or auditorily. Odors can become conditioned to experiential states and when later encountered have directional influences on behavior. Doing a frustrating task in a scented room decreases performance of other cognitive tasks in the presence of the same odor. Nonhuman animals communicate their emotional states through changes in body odor, and human body odors are indicative of emotional state. Human body odors 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 gay and straight 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. 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. ===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." If ingredients are listed on a product, the term "fragrance" can be used in a general sense. ==References== ==Further reading==

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