**4. Climate change: increase in allergens**

One effect of global warming is an increase in allergens. Allergens can be associated with various respiratory diseases such as Asthma or allergic reactions such as hay fever. An increase in hay fever can be attributable to global temperature increases due to synergistic effects of atmospheric warming on the pollination season of plants [44]. The observed rise in the number of airborne allergens is directly proportional to the increase in pollen content of the air [45]. From human health perspective, it can be expected that allergic reactions, as well as their severity, may worsen over time. This may be further exacerbated by the declining air quality, both indoors and outdoors [46, 47].

The decrease in air quality is compounded by other factors such as smoking, diesel fuel utilization, and the generation of nitrogen dioxide [48–50]. Temperature fluctuations also lead to mold formation and propagation [51]. This can further decrease air quality and can cause intense allergic response in some people [52, 53]. Some other common allergies include ragweed allergy causing hay fever and poison ivy causing contact dermatitis. **Table 1** lists a set of common allergens. When an allergen enters the body, its presence leads to an immune response featuring the sensitization of mast cells [54, 55]. When the allergen enters the body repeatedly, it attaches to the specific antibodies on mast cells resulting in mast cell degranulation, which leads to the release of histamine and other inflammatory mediators [56, 57]. Associated symptoms may include commonly encountered reactions such as watery eyes, itching, sneezing, and nasal/ sinus congestion. Pertinent to CC and global warming, it has been noted that patterns and distribution of common allergens typically present in different parts of the globe are changing [58]. The awareness and the ability to identify these patterns, coupled with modern mobile technology advances and point-of-care testing, will allow health-care providers to adequately prepare for the evolution and changing incidence of allergic reactions, especially in the context of preventive health measures and effective clinical management approaches [59–61].
