Allergies Can Kill, Intolerances Can't
Not a lot of people know, I didn't, that you have to be careful when saying "I'm allergic to that". There's a good opportunity that you probably are not allergic to it but just Intolerant to it. However you hardly ever hear people saying "I'm intolerant to that". Not sure why - maybe it's just because saying allergic is easier and more dramatic.
We're not trying to lessen the issue of Allergies just to make sure that you can use the right tests which will help you treating yourself but also to make sure that you know an allergy is to be taken very seriously while an Intolerance can be uncomfortable.
I also didn't relate Hay fever to being an allergy but it is and its official name is Allergic Rhinitis.
A food allergy is a reaction from your Immune System - your Immune System mistakenly treats proteins found in foods as a threat - the reason for anaphylactic shock from a nut allergy. Some Allergy symptoms to look out for are are a rash, wheezing and itching which can come on very rapidly just from eating a small amount of food. Common Food in adults is fish and shellfish and nuts while children can be allergic milk, eggs, peanuts, other nuts and fish.
A food intolerance doesn't involve your Immune System, there is no reaction similar to an allergic reaction and there isn't any threat to your life. Any symptoms, which normally affect the bowel and stomach can take many hours after eating the food which you may be intolerant to. It is probably only triggered when you eat a reasonable amount of that food unlike an allergy when a trace can cause a reaction.