What is an Allergy?

Allergies are one of the most common chronic diseases. An allergy is an abnormal reaction to a harmless substance called an allergen. An allergen means a substance that produces an abnormally vigorous immune response in which the immune system fights off a perceived threat that would otherwise be harmless to the body, such as pollens, foods, and house dust mite. This allergic reaction is due to a mistake of the immune system. The immune system protects us against invasion by harmful external agents such as bacteria or viruses that can cause infections, or own cells, such as tumor cells. But it must also be able to allow the entry of beneficial substances as the nutrients ingested with food. Allergens are tolerated without problems by non-allergic individuals. Most people have no problems being in contact with pets like cats, but when you are allergic to them you start to sneeze, you get an itchy and runny nose and red and itchy eyes.