The first page of this article gives a detailed account of what happens in the body during an allergic reaction. If you click the Next button at the bottom of the pages, it will take through the different types allergens, different reactions in the body, when to see an allergist and what an allergist does, different types of testing and so much more. There a numerous links at the bottom of the pages that cover allergy related subjects. The first page of the article is nice, but the rest of the pages are fantastic.