There are other ways in which our immune systems can cause allergic diseases. For example if you are allergic to nickel in jewellery or clothing, this is caused by quite a different part of our immune system. But it is still 'immunity gone wrong'. It was coined at the beginning of the 20th century to describe the fact that dogs immunised with venom proteins from another animal had fatal reactions when they had another injection of that protein. Most people use it to mean an illness produced by a reaction of our immune system to some protein or other substance.
Examples are hayfever, allergic asthma, food allergy, drug allergy, and infantile eczema.
There are two broad types of allergy as far as most people are concerned. The first kind is the common kind of allergy which causes hayfever, allergic asthma, food allergy, and some drug allergy. The second is a peeling eczema-like rash called contact dermatitis, which some people get from metals such as nickel in jewellery, watches or clothing items. It can also be caused by cosmetics, sticking plaster, or a variety of other things which come into contact with the skin. These two groups of allergic illnesses are completely separate, and having one kind does not mean you are more likely to have the other kind.