It comes from the Greek word allos meaning other. In the early twentieth century, the term allergy was first used to describe any altered reaction. Allergy is an extreme reaction to various substances that enter our body from the outside. Substances that have no effect on normal people can cause health problems such as hay fever, asthma, skin rashes (hives, eczema, contact dermatitis), anaphylactic shock, diarrhea and vomiting in some people. First of all, an allergic body is needed for the emergence of allergy.