Cause

Allergies may be largely due to genetic factors. If  the parents are allergic to substances, their children are also likely to be allergic and the allergy may be stronger in the children. It has been  observed that allergies have become more prevalent in the last few decades, especially  in urban areas. This may be due to the higher pollution levels and exposure to chemicals in urban area.

People in rural areas are less likely to suffer from allergies. Allergies are more common in affluent countries, where people live in a very clean environment and less exposed to parasites and other harmful pathogens. People in poor countries are exposed to pathogens in their daily life and so have a stronger immune system.