When people think of allergies what typically comes to mind is the standard allergy symptoms we all know or have experienced.  Our bodies may mistakenly identify a substance as toxic and produce antibodies against common foods or environmental substances.  This type of reaction is caused by IgE antibodies.  Allergic reactions to IgE antibodies can be severe and cause anaphylactic shock or even death.

There is another antibody, Immunoglobulin G (IgG), that can also cause allergic responses but the reactions are delayed.   This delay may make it difficult to identify the specific allergen that is causing the reaction and the discomfort may not be recognized as an allergy.  An IgG response may not occur until hours or even days after exposure to the allergen.  Symptoms may include headache, nausea, irritable bowel syndrome or other digestive issues, seizures or hyperactivity, making diagnosis difficult.

Not so long ago people, including many children, were subjected to hundreds of needle pricks containing different possible allergens to determine which ones caused the strongest reactions but this method is ineffective for IgG allergies due to the delayed reaction.  A simple blood draw can look for specific antibodies to hundreds of substances using only one needle.  The presence of the IgG and/or IgE antibodies will identify the allergen so that it can be avoided or eliminated from the diet.