WHO proposed a definition of Health, also contained in its 1948 constitution, that implies the bringing into play of a wide range of interrelated factors: biological, psychological and social: “Health is a state of complete physical, mental and social well-being and not simply the absence of disease or infirmity. The enjoyment of the highest possible standard of health is one of the fundamental rights of every human being, regardless of race, religion, political belief, economic or social condition”.
The environment has long been recognized as a key element, which together with the various spheres of social and economic life, has an impact on people’s health. Not only that, these spheres are themselves influenced by the increase in buildings, in complex and interacting ways (1).

In fact, over time, the densification of cities has made Europe a highly urbanized continent, which often led to the removal or degradation of the existing green space, not only in terms of quantity but also of quality (2). However, forecasts anticipate that within just over a decade the earth will be inhabited by about 8.5 billion people and nearly 10 billion by 2050, compared to the current 7.7 billion (3). The challenges following densification processes such as the loss of urban green space are all critical issues that affect the quality of life, the possibility of recreation, biodiversity and the provision of ecosystem services (4). Recent epidemiological analyzes have investigated the long-term impacts of four distinct urban environments characterized by traffic-related air pollution (TRAP), noise, natural spaces and neighborhood walkability, to understand the relationship with mortality, cardiovascular disease, chronic respiratory disease, allergy, type 2 diabetes, or reproduction. The results show that man’s interaction with this “built environment” can have a profound impact on his health. These exposures can be grouped into what is called “exposome”, that is a holistic measure of the environmental factors to which individuals are exposed during their life, considering both negative factors such as traffic and noise, and positive ones such as spaces natural (6).

The term “Green Infrastructure” instead, first introduced in the United States in the late 1990s, indicates an interconnected network of protected soils and waters that supports native species, maintains natural ecological processes, supports water resources and contributes to health and quality of life. Basically it supports the protection of natural systems from disturbing agents increased with urban development. Green infrastructure is so called to ensure that it is considered on a par with other infrastructures, and therefore requires to be planned and managed as an integral part of the urban structure. In general, there is ample scientific evidence regarding the ecological, social and economic benefits of urban green space, as well as being important for the appearance of the city and the quality of life. (5). The UGI, Urban Green Infrastructure, in addition to addressing the main challenges of urbanization, increases social cohesion, promotes the transition to the green economy, adaptation to climate change and the conservation of biodiversity (7). But above all, it is undoubtedly an important element in improving the quality of life in the city (8).

While it is increasingly evident that urban green space has a positive effect on the mental and physical level, potentially effective in improving the body’s immune system, at the same time it can also generate negative impacts on health, through high exposure to allergens (pollen), at the risk of contracting infectious diseases or skin cancers due to excessive UV rays. Good design and careful maintenance can certainly reduce or prevent many of these negative impacts (9). Certainly one of the concrete and indisputable disadvantages of plants for humans is allergenicity. In fact, the atmosphere hosts pollens, which represent the male element for the reproduction of seed plants, and when they reach the mature stage they are released to reach the female part of the flower, for the purpose of pollination. This occurs thanks to the transport of the wind in anemophilous plants or through insects in entomophilous ones. Basically, the pollen grain is characterized by a protective layer consisting of two walls: an external one called hexine and an internal one called intina (8). Respiratory allergy is the clinical expression of an immunological response considered inappropriate, as it is definitely exaggerated, towards airborne allergens often responsible for rhinitis, conjunctivitis and asthma (10). The study carried out on the allergenic potential of urban plants by Cariñanos P. et al presented another extremely relevant index from the point of view of environmental quality, related to the allergenicity of the urban green zone (IUZGA): underlines the need to consider the potential allergenicity of a species when selecting plant material to be used in cities to make urban green areas inclusive and non-exclusive in terms of public health (11).

As we all know, an integral part of the urban jungle is the urban forest, defined by an assembly of trees, shrubs and other plants that occupy urban and suburban areas. Mostly they have been planted by man, they produce powerful allergens that exist in large numbers. It is in effect an artificial structure that has exclusively anthropogenic origins. In consideration of this, allergy moves hand in hand with human behavior, i.e. people’s activities and places of activity determine the exposure relationships with allergens, translating them into sensitization and subsequent reactivity. The allergenic potentials of trees chosen at the design stage to be planted in new streets or gardens are not always considered, yet there are various references for developers to help with the suitable choice of vegetation, which can be consulted in order to avoid allergic implications. Almost every city follows a planting ordinance that draws on a list of species recommendations (12).

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