**3. Outdoor Allergens**

protective factor for allergic symptoms and allergic sensitization has still been under discus‐ sion. Studies have focused on the possibility that pet exposure might be beneficial as they can obstacle the development of atopic diseases particularly on the early years of life [43, 46]. Ownby et al. [44] suggested in his study that living with cats and dogs relates to a lower risk of developing atopy during childhood and young adulthood. Collin et al. [36] emphasises in their study that there is no relation between having a pet and bronchial response to metha‐ choline for an 8 year old child. The relation between exposure to allergens and allergy sensitization is a matter of discussion. The results of recent studies confirms hypothesis that keeping pets at home might lead to development of tolerance in a certain degree [46, 47].

Tobacco smoke is a public health issue and 25-35% of the people with asthma are regular smokers. Approximately 30% of the children has a difficulty to control asthma exposure to environmental tobacco smoke [19]. Environmental tobacco smoke affects individuals at all ages. Negatively, the effect of it on children is stronger, and they can not prevent themselves appropriately [13]. Passive smoking is the most important source of indoor air pollution [48]. Children are exposed to smoke not only at their homes but also in car, other public areas, or

The results of exposing to tobacco smoke at pre or postnatal stages are different. Exposure to maternal smoking at prenatal period has long-term effects on the respiratory health of children [50, 51]. Chemical substances available in smoke, transmits to the placenta and affects the health of fetal growth negatively [19]. Prenatal smoke exposure of the baby is associated with deficiency in both functional residual capacity and index of tidal respiratory flow. Further‐ more, maternal smoking is associated with increased serum IgE levels, and prevalence of skinprick test responses in children. Additionally, many studies have suggested that maternal smoking increase the risk of snarling respiration for children under 6–years old [52]. Smoking exposure size at prenatal period and lung irritation are the factors leading allergy development

Children whose parents smoke, experience more severe asthma symptoms and have exacer‐ bations more often [23]. It has been stated in Lang et al.'s [19] study that children exposed in indoor environmental tobacco smoke had more respiratory infections, and significantly worse asthma related quality of life. In addition to its prenatal relation with reduced airway size and its postnatal behavior as a proinflammatory lung irritant, some have proposed that environ‐

Tobacco smoke, affecting respiratory and circulatory systems, it the primary reason for many diseases and death, thus, it is a critical issue for public health throughout the world [19]. Although there are several interventions aiming at educating and raising consciousness in people, they are not common enough as desired. Unfortunately, such a public health issue is still waiting for a solution, although lots of strategies has been developed so for. The sole way to prevent children from tobacco smoke is to giving it up inside the house and to inform parents and family members about the mandatory tobacco education programmes helds at school. This is one of the recommended strategies to raise the awareness of environmental tobacco

restaurants. However, home is the most common place for exposure [49].

mental tobacco smoke might also affect allergy development [28].

**2.4. Environmental tobacco smoke**

6 Asthma - From Childhood Asthma to ACOS Phenotypes

[28, 48, 50].

People expose to outdoor allergens directly or indirectly is their life-span [53]. Controlling of outdoor allergens is more difficult than controlling of indoor allergens [1]. The most common sources of outdoor allergens are pollens, fungal spores, and air pollutions. Pollens are important risk factor for allergic rhinitis. Furthermore, they cause asthma through their particules penetrating lower respiratory ways. Some evidences suggest that exposure to pollens and airborne allergens increase asthma exacerbations. In order to reduce the pollen based respiratory symptoms, sensitized people should stay at home with closed windows at certain periods of the day that is an effective method to reduce allergen inhalation. Further‐ more, wearing masks in outdoor areas might be useful to reduce exposure [53].

Urbanization is an important contributor for asthma since it increases air pollution. Air pollution is a crucial risk factor for health and quality of life in urban life [54]*.* Children are more sensitive to air pollution and meteorological factors because their lungs have not completed development and developing immune and respiratory systems make them vulnerable to pathogens [55]. There is a consensus on the idea that air pollution might trigger asthma symptoms but the role of air pollution in the development of asthma is a matter of discussion. Air pollution is associated with asthma inflammation, increasing bronchial sensitivity, admitting to emergency departments and increasing rates in the use of drugs. The effects of air pollutants on lung functions depend on type of pollutants, their environmental concentration and duration of exposure to the pollutants. Airway mucosal induced by air pollutants and ruined mucociliary clearance facilitate transmitting and penetrating of aller‐ gens to immune system [56]. Concentration and nature of air pollutants changes among regions while the most common ones are ozone (O3), nitrogen dioxide (NO2), particulate matter (PM), sulfur dioxide (SO2), and carbon monoxide (CO) [53].

Modern lifestyle, emission gases of vehicles and air pollution are important risk factors for respiratory allergy for urban life. Controlling those allergens identified as outdoor is rather difficult however reducing exposure to those allergens might be an ideal approach [3, 38]. Individual efforts to control outdoor allergens might be insufficient since their sources are outdoor environment. Primarily, in order to reduce air-pollution based asthma inflammation high level ozone and PM2\*5 levels warning should be done, traffic should be reduced in urban areas, emission rates of vehicles should be controlled by local authorities [54]. On certain days when air-quality is poor patients should avoid outdoor activities and indoor activities should be included in asthma management plan. Air pollution is a global problem and the solution requires local national and international efforts by governments, industries and private sector authorities [55, 56].
