No doubt, you've eaten something in your lifetime that has upset your GI system. You may have been uncomfortable afterwards, with a vague idea that you don't feel well, or you may have had horrible vomiting or diarrhea. It may have lasted for days with you rushing repeatedly to the bathroom, with your stomach and intestine trying to get rid of what ailed you or it might have passed a few short minutes after you took some over the counter medicine.
If it happened just one time, you might have thought the food was tainted with some bacteria, virus, or parasite that got you sick. If it was a severe reaction, your doctor may have been particular questioning you about what and where you ate before it started and whether others you were with were sick as well. Or he may have ordered stool studies looking for the bug that may have caused your problems (and those of others in the community).
But if you've had the same problem more than once, bloating and gassiness after a meal, you may have figured that a food (not an infection) was the cause. You may have even suspected a specific food. It could be anything for any of a dozen reasons: your mother has similar problems with that food, or the neighbor down the street's great aunt's second cousin remembers reading about a certain food and those symptoms. Or you may have realized that you just don't feel well the mornings you have milk on your cereal for breakfast.
Does That Mean it's an Allergy?
Lots of Food Reactions exist: Coffee (or the caffeine in it) makes many people jittery. Greasy foods make some people nauseous. Carbonated beverages cause belching. Not one of those is an allergy. They are merely reactions that happen with specific foods--and they occur for a very large number of people.
Milk gives some people gas, discomfort or diarrhea--but that's not an allergy either. Rather it's an intolerance to the sugar, the lactose, in milk and many milk products. That's lactose intolerance. It 's a graded response. Some people can tolerate the amount of lactose in yogurt and soft cheese, and they can eat moderate amounts, but they can't drink much milk or ice cream. Others can't handle the small amount in even a slice of cheese
On the other hand, anyone with a true milk allergy-anyone who reacts to one of the milk proteins, can't take even the tiniest sip of milk without vomiting, spraying out a bright red rash or both. Again, that's a true allergy, one caused when a certain class of the body's gamma globulins (the IgE) cranks up an almost immediate reaction-one that tells the body not to consume any more.
One of the most impressive examples of that occurred in my office. A baby had severe vomiting and was there for evaluation. While in my waiting area, the baby crawled through an area where someone had spilled milk. the baby liked her hand and immediately began vomiting-severely enough that she almost required IV fluids so she wouldn't become dehydrated.
That's a big difference. The child with lactose intolerance can go to a birthday party and have a little ice cream to go along with the cake, but that would be devastating for the child with a true milk allergy
How Can I Tell?
Specific IgE blood tests and skin tests will usually show a significant reaction if there's an allergy. But most allergists will also want to know that the person actually reacts to the food, so they will take a detailed history of past events or they might recommend a controlled exposure to that food in their office or in an emergency room, in case the person has a severe response.
And for certain allergies that can provoke life-threatening reactions, like peanuts or shellfish, the allergist may recommend that the allergic person carry an EpiPen, so they can give themselves an emergency shot, should they unknowingly eat a food that even has a trace amount of the food they're allergic to. A little scary, maybe even a lot scary, but obviously very important to know and recognize.