Over the last decade, Hygiene Theory was thought to be the main cause for the explosive rate of food allergies. This theory is based on the hypothesis that we have become too clean in our daily living. In the past, it is believed that our immune systems developed by exposure to dirt, animals, and bacteria. Now that we live in a more hygienic world, the premise is that our immune systems have not fully developed and are turning on what should be innocuous substances (food) as if they were a mortal threat.
Because anaphylaxis is the response of the immune system known as an IgE, response, this theory bears some weight. The IgE response in humans is normally associated with the body’s fight against parasites. Yet in the modern, urban world, we rarely encounter parasites like our ancestors did, which may be causing the IgE to respond to certain foods instead.
This theory was brought into question more recently because it was largely based on the fact that third world countries, with their more rural populations and a lack of sanitation infrastructure, had lower rates of food allergies and autoimmune disorders. However, now that their rates of food allergies have begun to rise, this theory has lost some of its validity.
While Hygiene Theory may explain some, but not all, of the rise of autoimmune disorders, it's now recognized that our gut health has a much larger role to play than originally believed. The health of the microbes in our intestines, known as our microbiome, has shown in recent studies to have a significant effect on our immune system.
At this point in time, no one factor or combination of multiple factors has been determined to cause food allergies and autoimmune disorders. Clearly, more research is needed.