"Serious food allergies/intollerances is on the rise and no one knows exactly why that it."

There's been research which suggests that allergies/asthma/hayfever, etc may be related to eradication of intestinal parasites, esp. in first world countries. The research looked at the very low incidence of allergies in third world countries, compared to the high rate in first world countries. An increase in development of allergies was found when treatments for intestinal parasites were routinely administered in areas that had previously had very low allergy rates. Trial programs treating crohn's disease and irritable bowel syndrome using 'beneficial' parasitic organisms have had success in cases where conventional treatments do not.

The theory is that because the gut is designed to deal with parasitic organisms (some with more success than others), but basically doesn't get enough work in hygienic first world environments, then it 'finds' work to do by attacking things in our food and environment that we would otherwise not react to. Possibly in a few generations we will see a decline in the rate of allergies as we adapt to the change in environment.

This is not to suggest that exposing babies (with immature immune and digestive systems) to such environments is any solution to allergies - the flip side is that infant mortality rates are much higher in areas with uncontrolled bacterial/parasitic populations.

Sorry to jump off topic (it's not exactly related to introducing solids!!), but it's an interesting area of research. Anyone else come across it?