The incidence of allergies and asthma has been on the rise in recent years. Western countries have seen more of a rise than other countries. However, even in Asia and Africa, the allergies and asthma occur with higher frequency in urban areas than in rural ones.
The impact of industrialization on health is not a new concept. During the Industrial Revolution, people in the United States and Great Britain experienced a number of symptoms consistent with allergies, such as itchy and watery eyes, inflammation of the respiratory tract, and increases in the production of mucus. Public health experts often attribute enhanced allergy and asthma issues to reactions to the Industrial Revolution. Specifically, because decontamination, sterilization, and pasteurization measures were undertaken to reduce the incidence and spread of infection following the Industrial Revolution, people became less significantly exposed to diseases and bacteria. This reduction in exposure may carry with it the development of an overly sensitive immune system that is not well protected against allergies and asthma. Indeed, many countries today that do not have high health standards tend to have lower incidences of allergies than those with higher health standards.
In addition to our growing focus on cleanliness as we become more industrialized, we have also focused on efficiency, which may cause other issues related to asthma and allergy. For instance, we have created better means for insulating our homes to keep heat in, but these measures also increase the ability of dust and mold to stay and accumulate in our homes. These substances are common irritants to allergy and asthma sufferers.
Industrialization seems to promote allergies and asthma, but urbanization appears to do so as well. There is a significant amount of research showing that those dwelling in cities experience allergies and asthma more often than those who live in rural areas. Air pollution is widely blamed for the rise in these disorders in urban areas. Research aimed at supporting the hypothesis that industrialization increases allergies and asthma by causing air pollution has shown that animals exposed to air pollutants and allergens suffer synergistic effects that increase the impact of each irritant on the animals’ respiratory systems. In humans, air pollution caused by vehicles has been shown to aggravate asthma. Further, those living in highly populated cities may put even more emphasis on cleanliness, using sanitizers and anti-microbial products more often than those living in less heavily populated areas, who may worry less about the spread of germs.
Another problem for allergy sufferers in cities is the interaction that occurs between allergens and the air. Specifically, air pollution can react with irritants like pollen to produce compounds that are much more impactful on the human immune system. Other aspects of cities, such as their higher levels of carbon dioxide and generally higher temperatures can also increase the production of allergens like pollen and make them more likely to cause allergic reactions.
People often assume that cities are more protective against allergies than other areas because of their relative lack of trees and flowers. In response to this idea, the hygiene hypothesis was formulated, which suggests that growing up in rural areas can help build strong immune systems protect individuals against allergies later in life. Consistent with this hypothesis is the observation that children who grow up in cities do suffer from allergies more frequently than those who grow up in rural environments.
Though the increased exposure to microbes in rural areas is often viewed as a reason for better protection against allergy and asthma in these areas, researchers have also found asthma frequency to be high in inner city areas that have high levels of microbes. It has therefore been suggested that exposure to microbes may impact the likelihood of developing allergies but not asthma.
Given that the factors that are thought to contribute to rising allergy and asthma rates – namely, air pollution, global warming, and sanitation measures – are likely to continue or even increase, so too may the enhanced incidence of allergy and asthma. If we are going to slow the pace of allergy and asthma incidence, researchers will need to focus efforts on more clearly delineating what has caused the recent rise in these disorders and determining what can minimize the effect of those factors on allergies and asthma.