The prevalence of asthma and allergic diseases appears to have increased since the early 1960s, in particular in industrialised countries, with the rise in asthma occurring among both children and adults. Regardless of definitions, asthma and allergy must be seen as major public health problems. Changes in the genetic predisposition are not a likely explanation for their increase, since they would require several generations. Thus, the increased prevalence could be explained by changes in environmental factors, including indoor and outdoor environment. Air pollutants and indoor climate, as well as aeroallergens, have a link to climate change. Some recent studies indicate that a plateau in asthma prevalence may have been reached in some locations, but more efficient medicines may also play a role.
The associations between air pollutants and allergic sensitisation and asthma incidence are still not fully understood. However, a body of evidence suggests that urban living with high levels of vehicle emissions causes an increased risk. In addition, it is well documented that asthmatics are at increased risk of asthma exacerbations and emergency visits with increased exposure to ozone, particles and other pollutants as well as pollens. There is also increasing evidence for allergenic responses to exposures already during pregnancy.
Climate and climatic factors (temperature, wind speed, humidity, thunderstorms, etc) and air pollutants can affect the amount of pollens/allergenic particles and the potency of the pollen grains. Pollutants can modify both the morphology and the allergenic potential. Higher CO concentrations and a warmer climate may increase pollen quantity and induce longer pollen seasons, at the same time as levels of pollutants such as ozone may increase.
Not only pollen-induced asthma has a potential link to climate. Indoor climate and mites are also associated with allergy and asthma. In western Europe (57 ISAAC centres in 12 countries), the prevalence of asthma symptoms increased with estimated annual mean of indoor relative humidity, while altitude and the annual variation of temperature and relative humidity outdoors were negatively associated with asthma. These results suggest that climate affects the prevalence of asthma in children and may thus have implications for the assessment of potential health effects due to climate change.
Food allergies are immune-mediated reactions to foods mediated either by IgE antibodies or other immunological pathways. The prevalence of food allergy has been estimated as 1-3% in the general population and 4-6% in children, resulting in conditions ranging from mild to potentially life threatening conditions. Whereas children may outgrow their allergy, pollen allergics often secondarily develop allergy to food. Avoidance of the offending foods is the only practical means available to the allergic consumers.
Difficulties in the estimation of the frequency of food allergies in the general population stem from insufficient data and relatively little use of the standard diagnosis of food allergy because this only can be implemented under strict conditions and is often avoided in highly sensitised individuals. However, there is clear evidence that prevalence of (at least) atopy has increased over the last decade.