Food allergies occur when the body creates a certain type of antibody called IgE to food particles. The Antibody
IgE is the same type of molecule that results in other types of allergies, such as hay fever or allergies to bees and
medications.   In essence, with a food allergy, the immune system over reacts to something that is not normally
harmful to the body and the end result is unfortunately a reaction that can be very severe, even deadly.   The
symptoms of food allergies can vary and may include swelling of the lips, tongue, or throat, hives, abdominal pain,
vomiting, wheezing, and even death.   Most of the time, an allergic reaction to food will develop rapidly -within a few
seconds to an hour or two of ingesting the food.   Rarely, they can take much longer - one example is a delayed
allergy to red meat caused which is due to an allergy to a protein called galactose-alpha-1,3-galactose  ("alpha gal"
for short) and develops after tick bite.  Affected individuals typically develop allergic reactions from eating beef,
lamb, or deer meat 4-8 hours after eating.

How common are food allergies?
The public perception is that 20-25% of the population suffers from allergies, however the numbers are much lower:
3-4% of adults and 6-8% of children suffer from a food allergy.   The discrepancy is because there are a number of
food intolerances which are often mistaken for food allergies.   This includes lactose intolerance, celiac disease, food
poisoning, and many others.  Lactose intolerance results from the body being unable to break down lactose, causing
abdominal pain, bloating, gas, and diarrhea.   
Celiac disease results from gluten intolerance.   Gluten is found in many
foods, including oat and wheat products.    

Food allergies are much more common than they used to be.  The incidence of peanut allergies has doubled in the
past 10 years.    The most common food allergies in children are milk, egg, wheat, soy, and peanuts.  In adults, the
most common food allergies are peanuts and shellfish.    Most children with food allergies will outgrow them by  
early adolescence.  However, peanut and shellfish allergies rarely go away.    A family history of asthma,
environmental allergies, eczema, or food allergies are all risk factors for children to develop food allergies.   A child
with a brother or sister who is allergic to peanuts is 10 times more likely to become allergic to peanut compared to
the general population.

Recent studies seem to indicate that children with food allergies are also at higher risk to develop environmental
allergies and asthma later in life.

Sources include
Sampson HA.  Update on food allergy
J Allergy Clin Immunol 2004;113:805-819
Hong et al. Food allergy and eosinophilic esophagitis: learning what to avoid.  
Cleveland Clinic Journal of
What Are Food Allergies?

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