Smells surround a person every second of his life, although he does not always consciously feel them. The sense of smell — the ability to detect, recognize and perceive odors — is one of the oldest features of the human body. How does it work? The vast majority of mammals, including humans, have olfactory receptors that are sensitive to different groups of odors. They are located in the area of the nasal cavity in the so-called olfactory epithelium. These receptors react to volatile odorous substances and transmit signals of their presence along the olfactory nerves further to the olfactory bulb and then to the higher parts of the brain, where the information received is processed. As a rule, the more densely the epithelium is lined with olfactory cells, the sharper the sense of smell. According to various sources, humans have an average of 10 to 50 million such cells. But a dog has about 220 million, and therefore it is logical to assume that it senses smells more acutely. Because of this, and also because of the relatively small size of the olfactory organs, there is an understanding of the weak human ability to perceive odors. Yet many scientists believe that the human sense of smell is greatly underestimated. This is stated, for example, by neuroscientist John P. McGann from Rutgers University in his article “The weak human sense of smell — a myth of the 19th century.” In his opinion, the entire human olfactory system is much more complex than many imagine. For example, the same olfactory bulb is not inferior to mammalian organs in terms of the number of neurons and absolute size. And there are much more olfactory glomeruli attached to certain receptors and responding to odors in humans than in the most odor-sensitive animals. Even the cortical centers that interpret signals about aromas are larger and more complex in humans. In addition, American scientists have recently calculated that a person is able to smell and recognize not 10 thousand, as is often claimed in many sources, but about a trillion smells! It turned out that it captures many volatile compounds much better than animals. These scientists believe that humans have very good olfactory abilities and can distinguish a very wide range of odors.

The human brain interprets different smells in its own way. Scientists explain this in different ways: perhaps it’s all about differences in the “scent genes”, or maybe it’s a consequence of environmental influences (when the concentration of proteins that perceive odors changes under the influence of a particular fragrance). In one way or another, the brain associates different smells with different memories. But only with those, as it turned out, who caused a strong emotional experience at the time (both good and bad). This is confirmed by a study conducted by scientists from the University of Utrecht in the Netherlands. Experts gave several dozen subjects to watch tragic and shocking footage from the chronicle of the genocide in Rwanda. While watching in one of the rooms, they sprayed deodorant with the smell of currants. A month later, they were asked about the content of the film. The results showed that people who watched the fragrance-accompanied film gave a more accurate and vivid description of the scenes. Scientists explained all this by the fact that smells help a person to register strong and vivid emotions. This phenomenon is called the “Proust phenomenon” — on behalf of the French writer Marcel Proust, in whose books there is often a description of how any fragrance evokes certain memories. “The whole of Combray and its surroundings — everything that has a shape and has density — the city and gardens — floated out of a cup of tea,” recalls the main character of the work “Towards Swann.” The influence of aromas is so great that they are used as therapy to help restore lost memory, for example, due to the development of Alzheimer’s disease. For example, scientists from the UK conducted an analysis of research and found that essential oils of snowdrop, sage, lemon balm, periwinkle and a number of other plants can improve the cognitive abilities of patients with dementia. The famous Merlin Entertainments company recreates the smells of the past years in order to help Alzheimer’s patients. Her staff claim that odors such as tobacco, smoldering charcoal and peppermint can activate the olfactory memory of patients and evoke strong emotions. And the smell of carbolic soap, as the patients themselves note, has a calming effect.

Besides the fact that smells can associatively evoke certain memories, they can also influence a person’s social behavior. John McGann argues that the smell helps to recognize related individuals, which also affects sexual interest and provides information about another person’s anxiety or aggression. A 2015 study where scientists filmed participants with hidden cameras showed that people subconsciously sniff their hands after touching something and do it most often after shaking hands. The authors suggested that it most likely helps to detect other people’s chemical signals and works as an unconscious form of human communication. As for sexual behavior, British researchers from the University of Stirling have found that the smell of sweat can tell a woman a lot about a man as a potential sexual partner. In the experiment, 63 heterosexual women expressed their preferences by evaluating the sweat smell of different men, which they left on T-shirts. So they chose pleasant and unpleasant smells for them. Scientists have thus found another confirmation of the hypothesis that humans often use their sense of smell in much the same way as animals. By smell, both instinctively determine the quality of the immune system’s genes, which help the body destroy harmful bacteria and other pathogens. According to experts, women subconsciously choose partners with a different genotype to ensure the health of their future children. As described by Rachel Hertz, a neuropsychologist at Brown University, in her book “The Scent of Desire. By discovering our mysterious sense of smell,” a person’s reaction to odors can be determined by culture, social and historical aspects. For example, throughout life, the brain simply “learns” which smells are “good” and which are “bad.” In childhood, a person may like the smell that is considered bad in society, and under this pressure, the perception of the fragrance simply changes. Eskimos generally recognize only the natural odors of the human body: hair, sweat, urine. For these people, they will be a signal of safety and friendly contact. And the inhabitants of Northern Guinea often smear their skin with rancid lard — the smell of this product symbolizes prosperity and fertility. Renowned American neurologist and psychiatrist Alan Hirsch conducted a study to find out if there are such smells that create the illusion of a younger age and a more attractive figure. It turned out that the aroma of red grapefruit can have such an effect.: The weight of the participants who used such perfumes decreased to seven kilograms in the eyes of other people, and the age decreased by eight years. Thus, odors can even have an impact on the perception of physical attractiveness.

Interestingly, fragrances can enter the body not only through the nose, but also through other organs of the human body. Various scientists suggest that olfactory receptors may actually be found in the skin, lungs, prostate gland, skeletal muscles, and even in sperm cells. In particular, Hans Hutt, a molecular biologist from the Ruhr University in Bochum (Germany), found out that human skin reacts very well to the smell of sandalwood — “Sandalwood”. It turned out that skin abrasions heal better and faster by 30% if this fragrance is sprayed in the room. “If olfactory receptors are perceived as specialized detectors, rather than as receptors in the nose for detecting odors, then it makes sense that they can be located in other places,” says Jennifer Pluznik, associate professor of physiology at Johns Hopkins University. Together with her colleagues, she discovered that olfactory receptors help control metabolic function and regulate blood pressure in mice. Dr. Hans Hutt also proved that the prostate gland recognizes an ionone molecule with a pleasant floral scent, and this molecule stops the growth and spread of malignant cells, while blocking erroneous genes. This discovery, according to the scientist, will help in the development of a drug for prostate cancer. Hans Hutt also caused a stir in the scientific world when he stated that spermatozoa also have olfactory receptors and, thanks to them, they find the egg faster. According to the researcher, they “follow” the scent of lilies of the valley, which she is fragrant with. Biologist Grace Pavlat from Emory University has discovered olfactory receptors in skeletal muscles that respond best to the lyral molecule, which has a pleasant floral scent. It turned out that this smell promotes the healing of muscle tissue. Another study conducted by scientists from the University of Washington and the University of Iowa has shown that olfactory receptors can be found in human lungs. Experts have found that the neuroendocrine cells of the lungs can directly sense toxic volatile compounds and give a physiological response by constricting the airways. Since odors have a direct effect on the human body, it is not uncommon for a change in the sense of smell or its complete disappearance to be a serious “wake-up call” for the development of a dangerous disease. In general, anosmia — that is, lack of sensitivity to odors — is not the rarest thing on the planet. Most often, it occurs due to swelling of the mucous membranes and loss of sensitivity, for example, due to acute respiratory infections. However, in the absence of such causes, anosmia can be a symptom of the development of severe inflammatory processes in the body, cardiac and neurodegenerative diseases such as Alzheimer’s and Parkinson’s diseases. According to scientists from Sweden and the United States, after examining data on the health and mortality of more than 2,200 volunteers aged 71 to 82 years, olfactory disorders increase a person’s risk of death within 10 years by 46%, regardless of gender or race.

Some diseases have their own smell. Some of them are very clearly detected due to the pronounced unpleasant aroma, while others can be sniffed at. According to scientists, very soon experts will learn how to accurately determine human health by smell alone. If not with the help of human and animal noses, then certainly with the help of special testing devices. And the first steps towards this have already been taken. The most obvious thing that can be detected without special devices is ketoacidosis, an acute metabolic complication of diabetes. Its cause is an increased content of acetone in the blood, which is manifested by a specific pungent odor. Acetone (or ketone) bodies are an acid that occurs when the body begins to burn its own fats. The presence of these byproducts in the body can endanger human life. It is known that animals, in particular, mice and dogs, can recognize the disease by smell. As scientists suggest, perhaps the whole point is that the patient’s balance of certain substances in the body is changing, which animals can react to. Russian researchers from the I. M. Sechenov First Moscow State Medical University together with colleagues from the Institute of Ecology and Evolution. Severtsova RAS came up with a method for determining schizophrenia using the sense of smell of dogs. Interestingly, some scientists believe that humans can also sense schizophrenia. For example, biologist Hans Hutt claims that this disease has an earthy odor with an admixture of hay. Another test was developed by Israeli scientists from the Scientific Research Institute. Dr. Weizmann, who helps in the early diagnosis of autism in children. It is based on the simple fact that healthy children take longer to inhale pleasant scents with floral notes than, for example, the smell of rotten foods, but autistic children, as it turned out, do not feel this difference. The experiment showed that the subjects with autism inhaled both the smell of shampoo and the smell of rotten fish in exactly the same way. They also learned to identify Parkinson’s disease by smell. Despite the fact that loss of sense of smell can be a symptom of this developing disease, the patients themselves, as it turned out, may have an unusual smell. It all started back in the 1980s, when nurse Joy Milne began to notice a strange scent of musk coming from her husband. A few years later, Tom was diagnosed with Parkinson’s disease. Neuroscientists from the University of Manchester became interested in the nurse’s ability to detect a disease by smell and conducted several studies. During one of them, they identified specific volatile compounds, including hippuric acid, eicosane, and octadecanol. The production of such compounds in the body indicates a change in neurotransmitter levels, which is one of the symptoms of neurodegenerative disease. Subsequently, the scientists turned to Joy Milne again, and she confirmed that this is exactly what “the disease smells like.” Currently, researchers are developing a test based on this technique for early diagnosis of Parkinson’s disease.

Professor Hans Hutt is confident that the sense of smell can be trained. And the well—known example serves as proof of this – the remarkable abilities of perfumers who know well how to handle scents. The scientist notes that any perfumer needs to practice for at least an hour before starting work: inhale different scents — rose, lemon, vanilla — and determine what kind of fragrance it is. This is very similar to the work of wine tasters, for example, who train in the same way to accurately identify the type of drink, the country of origin, and the characteristics of the vine. There is an opinion that people are born with a similar sense of smell as a perfumer. However, this is not true: in experiments with novice and experienced perfumers, French scientists from the University of Lyon have found that the ability to detect and identify hundreds or even thousands of odors depends almost entirely on preparation and exercise. Therefore, you can “train your nose” in the same way that athletes train their bodies or pianists train their fingers. In his book “No One Smells as Good as You,” Dr. Hans Hutt says that even two five-minute approaches a day will be enough to improve olfactory abilities, and during this time you need to inhale an intensely smelling fragrance, be it a flower or an essential oil. Then it is necessary to associate this fragrance with a certain association. Then, the scientist concludes, it will be possible to significantly reduce the risk of deterioration of the sense of smell with age, as well as improve well-being and memory. Photo: indiadaily.ru