Air pollution and climate change have a significant impact on human health and well‐being and contribute to the onset and aggravation of allergic rhinitis and asthma among other chronic respiratory diseases. In Westernized countries, households have experienced a process of increasing insulation and individuals tend to spend most of their time indoors. These sequelae implicate a high exposure to indoor allergens (house dust mites, pets, molds, etc), tobacco smoke, and other pollutants, which have an impact on respiratory health. Outdoor air pollution derived from traffic and other human activities not only has a direct negative effect on human health but also enhances the allergenicity of some plants and contributes to global warming. Climate change modifies the availability and distribution of plant‐ and fungal‐derived allergens and increases the frequency of extreme climate events. This review summarizes the effects of indoor air pollution, outdoor air pollution, and subsequent climate change on asthma and allergic rhinitis in children and adults and addresses the policy adjustments and lifestyle changes required to mitigate their deleterious effects.

The impact of climate change on the environment, biosphere, and biodiversity has become more evident in the recent years. Human activities have increased atmospheric concentrations of carbon dioxide (CO2) and other greenhouse gases. Change in climate and the correlated global warming affects the quantity, intensity, and frequency of precipitation type as well as the frequency of extreme events such as heat waves, droughts, thunderstorms, floods, and hurricanes. Respiratory health can be particularly affected by climate change, which contributes to the development of allergic respiratory diseases and asthma. Pollen and mold allergens are able to trigger the release of pro‐inflammatory and immunomodulatory mediators that accelerate the onset the IgE‐mediated sensitization and of allergy. Allergy to pollen and pollen season at its beginning, in duration and intensity are altered by climate change. Studies showed that plants exhibit enhanced photosynthesis and reproductive effects and produce more pollen as a response to high atmospheric levels of carbon dioxide (CO2). Mold proliferation is increased by floods and rainy storms are responsible for severe asthma. Pollen and mold allergy is generally used to evaluate the interrelation between air pollution and allergic respiratory diseases, such as rhinitis and asthma. Thunderstorms during pollen seasons can cause exacerbation of respiratory allergy and asthma in patients with hay fever. A similar phenomenon is observed for molds. Measures to reduce greenhouse gas emissions can have positive health benefits.

Projections of the effects of climate change on allergic asthma: the contribution of aerobiology. Allergy 2010; 65: 1073-1081.There is unequivocal evidence that the climate is changing and at an increasing rate. Global average temperature has increased by more than 0.7°C over the past 100 years, and the Intergovernmental Panel on Climate Change (IPCC) projects that the average global surface air temperatures in the years 2090-2099 are likely to be between 1.8 and 4.0°C warmer than those in 1980-1999, depending on which climate scenarios are input into the models (1). In addition to global warming, some regions, including northern Europe, are projected to experience increased rainfall while others, including the Mediterranean, are expected to experience substantial droughts. Extreme weather events, such as heat waves, heavy precipitation and thunderstorms, are also predicted to increase over the next few decades. These changes are as a result of increases in atmospheric carbon dioxide (CO 2 ) and greenhouse gases in which anthropogenic activities play a key role.All the above climate-related factors can impact on the physiology and distribution of living organisms, such as plants and fungi. In this context, there is evidence that climate change affects pollen and spore production by plants and fungi as well as different phenological events. At the same time, current changes in climate are affecting the different aerobiological processes (emission, dispersion and/or transport, and deposition) of aeroallergens. AbstractClimate change is unequivocal and represents a possible threat for patients affected by allergic conditions. It has already had an impact on living organisms, including plants and fungi with current scenarios projecting further effects by the end of the century. Over the last three decades, studies have shown changes in production, dispersion and allergen content of pollen and spores, which may be region-and species-specific. In addition, these changes may have been influenced by urban air pollutants interacting directly with pollen. Data suggest an increasing effect of aeroallergens on allergic patients over this period, which may also imply a greater likelihood of the development of an allergic respiratory disease in sensitized subjects and exacerbation of symptomatic patients. There are a number of limitations that make predictions uncertain, and further and specifically designed studies are needed to clarify current effects and future scenarios. We recommend: More stress on pollen/ spore exposure in the diagnosis and treatment guidelines of respiratory and allergic diseases; collection of aerobiological data in a structured way at the European level; creation, promotion and support of multidisciplinary research teams in this area; lobbying the European Union and other funders to finance this research.

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