Allergy is an unjustified and exaggerated defensive reaction that not only does not contribute to health but may cause serious health problems. Allergies can present with different symptoms which are explained in the section of each particular allergic disease.
At this point we will recall typical allergic symptoms such as an itchy rash, swelling, sneezing, runny nose and shortness of breath.
The immune system, which is responsible for protecting the body against harmful environmental organisms, may establish a reaction (an allergic reaction) when it mistakenly identifies an environmental factor as harmful.
Having said that, allergies may also be secondary to a dysregulation of the immune system, without the involvement of an environmental factor. In these cases, the immune system triggers an allergic response and a failure in the regulation of the immune system allows the response to propagate.
It is important to remember that sometimes autoimmune diseases (diseases in which the body attacks itself) may manifest with allergic symptoms.