I have people ask me if we have food intolerances or food allergies. There is a difference and I'll do my best to explain the difference between the two. Please keep in mind that I have no formal training on the subject, only my experience and information I've gathered from reading and researching. Don't forget to consult a health care professional before changing your diet. :)
I'll use the example of milk to explain the differences between the two.
When you have an intolerance to milk, your small intestine doesn't produce enough of the enzyme lactase to break down the milk sugar, lactose, into two simple sugars, glucose and galactose, to be absorbed by the bloodstream. The lactose then moves from the small intestine to the colon where bacteria break down some of the lactose, turning it into hydrogen. The rest of the lactose then draws water into the colon. The result of hydrogen gas and water in the colon is not so fun: cramping, diarrhea, bloating and flatulence.
When you have an allergy to milk, the problem is with your immune system thinking that the milk proteins (casein and whey are the main components) are an invading antigen like a bacteria/virus/chemical. The immune system creates antibodies (immunoglobulins) so that next time the invader is discovered, the white blood cells destroy the antigens. With a milk allergy and any food allergy, the immune system has this over-exaggerated response to harmless antigens. Symptoms of a milk allergy are no fun either and can vary in severity from person to person. They can be: skin reactions (rash, hives, eczema, allergic 'shiners' or dark circles around the eyes, swelling of the lips/mouth/tongue/throat/face), stomach or intestinal reactions (cramping, diarrhea, abdominal pain/bloating, flatulence, vomiting) and/or nose/throat/lung reactions (runny nose, sneezing, watery/itchy eyes, coughing, wheezing, shortness of breath).
Boy2's allergies: most diary, grapefruit, orange, lemon, eggs, wheat, rye, soy, spelt
My allergies: most dairy, eggs, sugar cane, almonds, hazelnut, flaxseed, wheat, peanut, quinoa, rye, spelt, kamut. I'm also vegetarian, which isn't because of allergies, but by choice.
We had our food allergy testing through our naturopathic doctor. We had Allergy IgG - IgE testing done. Which tests for antibodies (immunoglobulins) in the blood to the different foods. For the testing to be accurate, you have to consume foods you may be allergic to for two weeks prior to testing so there are enough antibodies in the blood.
For more scientific info on the testing go to Rocky Mountain Analytical: