Why does it seem like so many people have food allergies these days?

It seems like these days everyone has some kind of food allergy - peanuts, milk, nuts, soy, gluten (usually intolerance, not allergy), food dyes, etc.  About 4% of the U.S. population has some kind of food allergy. The most common food allergy is peanuts, and the best available numbers say that peanut allergies in children doubled between 1997 and 2002 - just 5 years!  Food allergies can result in symptoms like rash, hives, and swelling of the throat and constriction of the airways.  The most severe forms can result in anaphylactic shock - an extreme overreaction of the immune system that can result in death in rare cases.  So what causes a food allergy?  A food allergy happens when your immune system recognizes food as something dangerous and foreign, and not simply just food.  Immunoglobulin E (IgE) is a class of antibodies in your body that recognize foreign threats, and also bind to food allergens.  A specific IgE detects the culprit food (it can be on your skin, in your mouth, or in your digestive system), and binds to mast cells and basophils, where it triggers the release of histamines and inflammatory signals.
So why does it seem like we have so many more food allergies nowadays?  One possible explanation is the "hygiene hypothesis."  The hygiene hypothesis states that we live in such a clean, sterile environment that our immune systems do not "learn" correctly when we are very young, and therefore tend to develop overreactions to harmless things, like food and pollen.  This is supported by evidence that food allergies (and others) increase with increasing affluence and cleanliness of the population.  Think about how many of us used to live - perhaps on a farm, tilling fields, milking cows, raising livestock, and surrounded by a plethora of immune system "challenges" from birth.  Nowadays, we live a much more comfortable, clean life.  Our immune systems were designed to encounter and "learn" from foreign agents, and without the learning process our immune systems go haywire.  Another difference is that we have almost eliminated parasitic organisms that used to live in our digestive systems - worms are an example.  Worms and other parasites used to be a reality of human existence, but no more.  IgE is also the antibody that is charged with defending us against parasites - and now it has very little to do!  There is a lot of work being done in this area right now, but so far it looks like the hygiene hypothesis may partially explain all of our food allergies.
Another hypothesis is that we are more aware and pro-active about diagnosing food allergies.  We worry more about simple rashes or an outbreak of hives, and get tested with an allergist to identify the culprit.
Now don't get me wrong - our clean lives help us to avoid infectious diseases and other problems that plagued our ancestors - but maybe we can find a middle ground.  Let the kids play in sandboxes, jump in mud puddles, visit the petting zoo and the beach, get a dog, go for hikes in the woods, and lay off the hand sanitizer sometimes.  And if you do have a food allergy - you're not alone.  These days, there are loads of alternatives that make eating around your allergy way easier than ever before.