1. Nepal Medical College and Teaching Hospital (NMC), Nepal: parshu_ram23@gmail.com
2. Nepal Medical College and Teaching Hospital (NMC), Nepal: asbin.bandhari11@gmail.com
3. Nepal Medical College and Teaching Hospital (NMC), Nepal: parshukirby88@outlook.com

 *             Correspondence: parshu_ram23@gmail.com

Keywords: allergens, pollutants, aeroallergens, symptoms, sensitivity

1. INTRODUCTION

A major risk to one’s health is air pollution (AP). Carbon monoxide (CO), ozone (O3), nitric oxides (NOx), sulfur oxides, and particulate matter (PM) are among the complex mixtures of liquids, solid particles, and gases that make up this environment [1]. Based on particle aerodynamic equivalent diameter, inhalable PM is further separated into three categories: coarse (2.5–10 m), fine (0.1–2.5 m), and ultrafine (0.1 m), with fine PM having the ability to enter the lungs. Coarse PM cannot reach the lungs, while fine PM can [2]. In cities, heating systems and transportation are common sources of emissions. Gaseous emissions (like NOx) and non-combustion sources (such road dust, tire wear, and brake wear) combine to create traffic-related AP [3]. Nitrates, O3, and organic aerosol are produced by these significant emissions. Heater systems are a significant source of PM and CO pollution. PM is also a product of the business [4, 5]. An increasing number of allergies are linked to ailments that affect public health worldwide [6]. Asthma is the most common chronic pediatric illness, affecting 339 million individuals globally. Sensitization to ambient aeroallergens is also widespread; prevalence rates range from 17% to 50% among 20–44-year-olds in 35 sites across 15 developed nations [7]. Aeroallergens cause higher irritation in atopic people [8]. Thorough epidemiological research has been conducted to examine the connection between asthma and respiratory health. Given the increasing need for green space and the elevated levels of some air pollutants, it is imperative to comprehend the ways in which allergies and pollutants interact in urban settings [9]. It is anticipated that climate change may raise pollen and spore counts as well as the concentration range of numerous airborne contaminants (such as CO, ozone, and extreme dust occurrences). Consequently, it is critical to comprehend the impact that co-exposure to allergens and pollutants has on the human body. This review article reviews and summarizes the epidemiological evidence about the many forms of aeroallergens, their potential mechanisms, their interactions with air pollution, and their effects on biological systems.

2. MATERIALS AND METHODS

For this systematic review, three databases were searched: PakMediNet, PubMed, and Google Scholar. Articles published between January 2019 and June 2023 were the focus of our search. MeSH and non-mesh terms, including allergens, aeroallergens, and outdoor pollutants The keywords used were particulate particles, diseases, severity, and symptoms. Both AND and OR were boolean operators. Not included were articles that weren’t published in English. Furthermore, the method by which the studies were selected did not. Viewpoints, case reports, case series, meta-analyses, clinical trials (RCTS), and grey literature are all included. The following inclusion criteria were met by the articles that were discovered through pertinent database searches. Released within the last five years is the article. Among these were pieces. After removing duplicates, the three writers independently examined the titles and abstracts in light of the eligibility requirements. Reading each selected article through to the end was the next stage. Papers were written by the three selected authors. In case there is any uncertainty, the other authors examine the articles to verify their eligibility. A material extraction sheet was made and the PRISMA criteria were followed. All relevant data was gathered by adhering to the selection criteria. We reduced the total number of articles to 606 by applying the following exclusion criteria to the abstracts and titles. Papers regarding COVID-19’s effects on respiratory disorders, food allergies and genetic sources of allergies, occupational allergens and climate change, and papers written in languages other than English were all disqualified. After carefully reading the remaining articles, the final 20 that met the requirements for inclusion were selected. Geographical parameters were also established. Among these were pieces.

3. RESULTS AND DISCUSSION

Because they have the potential to produce allergy reactions in certain individuals, pollens, spores, and other biological or non-biological airborne particles can all be categorized as aeroallergens. Aeroallergens can be inhaled or come into touch with the skin, and when they do, the skin and mucous membranes react allergicly, releasing proteins [10]. Additionally, airborne particles have the ability to cause annoying reactions without triggering an immune response. Allergies can also be induced by certain reactive allergenic substances and allergens originating from live organisms. These chemicals are usually found in industrial workplaces more often than in regular homes. But common household objects—like the isocyanates found in bathtub refinishing products—may include immunogenic compounds [11–14]. Some people may be allergic to the spores that molds that grow indoors discharge into the air. While mold and mildew may grow practically anywhere there is moisture, they are particularly happy in moist areas such as basements, restrooms, and other locations where water seeps. Indoor plants, particularly those kept in damp wicker baskets, might serve as a source. Other indoor spaces that are susceptible to mold growth include storage closets, behind furniture, old foam rubber pillows, and mattresses [15, 16]. Spores and other byproducts that are sources of allergies are dispersed outside by fungi. While millions of fungi are known to cause indoor air pollution, only a small number of species have been shown to contain pure allergens, and none of them have been thoroughly studied. Fungal spore allergens have been linked to the development of hay fever, asthma, and hypersensitivity pneumonitis. Additionally, other fungal compounds may be toxic or irritating, which may exacerbate pre-existing allergic disorders [17–19]. Outdoor allergies are mainly triggered by environments that are naturally occurring. Among the most frequent outdoor allergens are mold and pollen from ragweed, grass, and trees. The sensitivity to seasonal triggers and allergens accounts for the majority of cases of outdoor allergies. Outdoor allergies are typically caused by mold spores and pollen [20]. As with pollen from other plants, some people may be allergic to tree pollen3. Trees in the south can begin producing pollen as early as January, even though the majority of tree pollen is released in the spring [21]. Grass pollen is the allergy that most people have hay fever from. Late April is when the grass pollen season peaks. You may have a grass allergy if you experience outdoor allergies that get worse throughout the months of April through June [22]. The mid-September peak of ragweed pollen is observed in certain states as early as June 6. Any of the 17 species of ragweed that are prevalent in 49 states across the US could be the source of symptoms [23]. Many commonplace items, such as compost piles, leaves, crumbled wood, and grains, can harbor mold. When these surfaces crack, mold spores are released into the air, where they can be swallowed by people in the vicinity [24]. Pollen grains are produced in the spring, summer, and fall by trees, weeds, and grasses. A common airborne allergy is pollen, particularly in the spring and summer when temperatures are high and flowers are in bloom. A wide variety of grasses produce pollen, such as orchard grass, Timothy grass, and Kentucky bluegrass, to mention a few. While annoying reactions can affect anyone, allergies can only impact individuals who are genetically prone to them. Allergens in the air, whether indoors or outdoors, can exacerbate allergic asthma, even though most people in developed nations spend over 90% of their time indoors. In addition to other animal dander like cat, dog, and bird droppings, dust mites can cause anthracnose and other respiratory illnesses (see the graphic below) [25–27].  Anything that causes an allergic reaction in humans is known as an allergen. An allergy is defined as an immune-mediated hypersensitivity brought on by exposure to an allergen. It is separated into two phases: the first is called sensitization and is characterized by an immune diversion toward a Th2-type response. Th2 cells specific to allergens contribute in this process by secreting cytokines such as IL-4, IL-5, and IL-13. Mast cells containing IgE are activated in the second stage [28], which leads to an allergic reaction in the subsequent stage (i.e., histamines, prostaglandins, leukotrienes). People who have respiratory allergies consequently have a wide range of symptoms. The most common allergic reaction is mediated by immunoglobulin E (IgE) antibodies produced by the immune system [29]. Mast cells are also essential since they carry histamine and other inflammatory chemicals. After being exposed to an allergen for the first time, a person becomes “sensitized” to that allergen. An IgE antibody specific to an allergen binds to the surface of the mast cells in the body, making a person “sensitive” (or “hyper-sensitive”) to further exposures to the allergen. When a sensitized individual is reexposed to the same allergen, mast cells produce histamine and other chemicals associated with an inflammatory reaction. When these substances come into contact with nearby tissues, they trigger an allergic reaction and the symptoms we commonly associate with allergies. sixteen Atopy, a hereditary predisposition to allergies, causes a significant increase in IgE production compared to normal. Years after being exposed to an allergen, the human body can continue to manufacture IgE antibodies. Even in adulthood, a person who was allergic to penicillin as a youngster may still remain so [30]. The reason why some people have allergies while others do not is unknown. There is no question that a person’s ancestry plays a major role in determining whether or not they have allergies. A child born to an allergic parent has a three-to-one chance of developing allergies themselves [18]. The Allergen City of fungus spores and plant pollen is altered by outside air pollution, which also speeds up the release of allergens and makes it easier for them to enter the respiratory system. Air pollution affects the epithelium, which can increase oxidative stress, inflammation, and weaken the immune system, all of which might worsen an allergic reaction [30]. Numerous human investigations have shown that allergies and air pollution negatively alter biological outcomes. When they are simultaneously exposed to air pollution, the inflammatory and immunological reactions brought on by allergens are intensified, lung protein expression is changed, and lung function is compromised [31]. Epidemiological research on allergen-pollutant interactions at ambient level has shown contradictory findings [17]. Climate change affects airborne allergens by changing the distribution and allergenicity of fungal spores and allergens themselves. Over an extended period of time, a number of studies have linked patterns in pollen season to variations in temperature. In Ourense, Spain, oak pollen patterns have been studied since 1993 [32]. It was discovered that the annual increases in pollen peak concentration and high content were 7.5% and 7.9%, respectively. Apart from pollen and fungus spores, dust mites, mold, and interior fungi are also significantly impacted by climate change. Climate change has been found to have an impact on house dust mites (HDMs), their allergens, and allergy illnesses. This suggests that natural HDM development, allergen generation, and survival may be altered by local or global variations in temperature, humidity, air pollution, or other environmental factors. Depending on how easily they can enter the body, where they settle, and how they interact once there, the constituents of air pollution can be harmful to human health. The human body is exposed to air pollution and allergens through inhalation and ingestion. The immunological, cardiovascular, neurological, and respiratory systems are the most frequently impacted by air pollution [33]. The majority of human exposure occurs from inhaling fungus spores and pollen grains. Thru the respiratory system, the body is exposed to pollen and fungal proteins. Antigens here lead to inflammation. “Skin-prick tests” will identify any allergies. At a “pricked” location on the skin, these tests demonstrate Type I hypersensitivity mediated by IgE. Seasonal allergic rhinitis is mostly caused by grass and tree pollen. When aeroallergens impact the respiratory system depends on their magnitude. The range of aeroallergens is 10–100 m. 10 m is very little, 10–25 m is small, 26–50 m is medium, 51–100 m is huge, and >100 m is extremely large. Grain sizes of aeroallergens more than 5 m adhere to the nasal mucosa and conjunctiva of the eyes. They can exacerbate asthma and induce allergic rhinitis or conjunctivitis. You get asthma from these particles. There are differing inflammatory reactions [21, 30]. IgE-mediated chronic immunological response is elicited by aeroallergens. Increases in interleukin-4 (IL-4) control IgE-mediated atopic reactions. Allergies and asthma have increased across all age groups. An immune-mediated respiratory condition is asthma. Children with asthma frequently go through the “atopic march.” Allergies associated to aging produce transient symptoms. Allergies to food (like eggs) and indoors (like dust mites) come first, then outdoor (like pollen) allergens. The earliest windows for environmental exposure are probably during pregnancy and the first few months of life, as “atopic march” symptoms might appear in the first year of life. The only times an illness can be influenced are before its symptoms appear, because both airborne particles and antigens are able to pass through the placental barrier [34]. If exposure to the environment lowers the chance of developing a particular condition, it is protective. Early exposure to dogs or cattle reduces the risk of developing aeroallergen sensitization and other respiratory diseases associated to allergies in children. According to hygiene hypotheses, microbial exposures cause the immune response to shift toward Th1 predominance. Aeroallergen sensitization can be prevented by early and prolonged animal contact, particularly during the first two years of life. Exposure to aeroallergens reduces the development of IgE antibodies specific to that allergen in farm animals [35]. A youngster that is breastfed is less likely to develop asthma or eczema. Exclusive breastfeeding lowers the risk more than expressed breast milk or breast milk combined with formula, while atopy in the mother may obscure this association. Children ages 0 to 2 have the greatest reduction in risk [36]. In order to classify an environmental element as a risk factor, a positive exposure-response association must be demonstrated. The following environmental factors and pollen have been related to allergy illness. The seasons affect pollen counts. If there aren’t any strong winds or considerable rain, ragweed pollen peaks at noon. Variations in wind, humidity, and temperature can affect the number of evening counts. Water can increase these aeroallergen productions in a matter of 24 hours [37].  Owing to fractured aeroallergen grains, high counts might not be necessary for considerable aeroallergen exposure because of the intricate nature of precipitation. Asthma exacerbations can be brought on by thunderstorms, which raises emergency room (ER) visits and death. Pollen grains, both whole and broken, are transported to the earth by thunderstorms and then dispersed by wind currents [38]. The rise in airborne allergens and respiratory disorders is a result of climate change. In light of these dire forecasts, mitigating efforts against climate change are imperative. By addressing climate change, we can lessen the effects of global warming on aeroallergens and allergy-related respiratory disorders by increasing temperature and reducing CO2 emissions. Adapting to climate change is a critical component in mitigating it [39]. Healthcare professionals are required to advocate for adaptation and mitigation of the climate catastrophe as they gain importance. Although alternatives to adaptation have been mentioned, not much thorough research has been done on them up to this point [40]. Policy design, planting methods, and allergy control are recent study topics. A study was conducted to examine the effects of ragweed (A. artemisiifolia) on community health as well as the effects of an unintentional introduction of a leaf beetle on patients with ragweed sensitivity and healthcare costs [23]. According to their research, invasive non-native weeds like ragweed can reduce healthcare expenses, morbidity, and mortality. Airborne allergen monitoring is a key indicator of climate change health. There has been a call for an integrated approach to air quality monitoring that takes into account the physical, chemical, and biological interactions present in the atmosphere. Smartphones have made it feasible to monitor pollution exposure, allergens, and weather conditions in real time [41].

4. CONCLUSION

Air pollution (AP) is a serious health hazard. It is a complicated mixture of liquids, solid particles, and gases that includes things like ozone (O3), carbon monoxide (CO), sulfur oxides, nitric oxides (NOx), and particulate matter (PM). Inhalable PM is further divided into three categories based on particle aerodynamic equivalent diameter: coarse (2.5–10 m), fine (0.1–2.5 m), and ultrafine (0.1 m), with fine PM being ible to enter the lungs. Fine PM can enter the lungs, while coarse PM cannot. Common sources of emissions in cities are transportation and heating systems. Traffic-related AP is caused by a combination of gaseous emissions (such as NOx) and non-combustion sources (such as road dust, tire wear, and brake wear).3 These large emissions produce organic aerosol, nitrates, and O3. One major source of PM and CO pollution is heating systems. There is another source of PM: the industry. It is significant to remember that the creation, concentration, seasonality, and dispersion of aeroallergens are all directly impacted by air pollution. Climate change has the potential to extend the season of aeroallergens and raise the allergenicity of pollen grains. Pollen allergens will rise as a result of these changes. Asthma and lung allergies are predicted to increase in frequency, as are the costs associated with their treatments. Typical airborne allergies include mold and pollen. Typical airborne allergies include mold and pollen. Allergies are caused by aeroallergens, particularly in those who are genetically predisposed. Fungi and pollen cooperate. Allergies may be brought on by or caused by aeroallergens. Once a person becomes sensitive and experiences symptoms, more exposure to risk factors may exacerbate those symptoms. When a person receives medical attention or removes himself from risk factors, their symptoms go away. An aeroallergen warning system could alert someone who is allergic to aeroallergens and advise them to reduce their exposure. An alarm system would benefit from a model of the production and dissemination of aeroallergens that takes climate change and weather into account. Air quality can be predicted by this model. Humans respond to comparable pollens in similar ways. Though species counts are still helpful for modeling and study, it would be simpler and less expensive for the public to record total amounts of tree, grass, and ragweed pollen. Longitudinal studies are necessary for the investigation of long-term trends rather than seasonal and allergy changes. This kind of research is necessary to better understand how pollens and fungi are impacted by climate change. In order to close the many gaps in our understanding of this complex topic, more research is required. This includes expanding the geographic scope to include Antarctica, improving methodological approaches, and realizing that, given the mechanical, biochemical, and biological components of the atmospheric environment, air quality monitoring and assessment now require a more cogent and comprehensive approach.

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