Studies have shown a number of possible factors that may be contributing to the rise in allergies. The most prominent, the Hygiene Hypothesis, theorizes that modern day hygiene creates a bacteria-free environment, which prevents an active immune system in early childhood. This may be causing the immune system to become more prone to allergies since the defense system is not challenged by harmless bacteria. Children who are exposed to such bacteria earlier in life appear to have reduced risk in developing allergies by boosting immune activity.
However, the rise in allergies may also be a consequence of the changing environment. Christine Rogers Ph.D., a research associate in Environmental Science and Engineering at Harvard University explains that there have been significant increases in allergies and asthma in recent decades, which cannot be explained by any change in genetics.
According to Rogers, global warming is having an impact on the growing season with spring occurring earlier in most places. Along with an increase in carbon dioxide levels, this will result in longer and more intense allergy seasons in the future. Based on their studies, it is estimated that pollen production in ragweed can be expected to increase significantly from predicted future climate conditions.
Aeroallergens are becoming more abundant due to climate change and causing more cases of allergies with stronger reactions. Paul Epstein, M.D., co-director from the Center for Health and the Global Environment at Harvard confirms that global warming is directly affecting pollen production. From the atmosphere becoming more clogged with carbon dioxide, plants are responding by producing more allergens. Higher rates of asthma are expected due to higher levels of pollen and changes in the types of molds brought about by global warming.