An allergy is when your immune system overreacts to a substance (allergen) in the environment. It can often cause inflammation. Allergies are not infectious and can develop at any time in a person’s life. If your parents have allergies, it can increase your likelihood of developing an allergy, but it’s not a certainty. In other words, a child whose parents have allergies can live his or her whole life without ever developing one, and a child whose parents don’t have allergies might develop one, even at the age of 60.
This question was answered by Carsten Schmidt-Weber, Director of the Center of Allergy and Environment (ZAUM), a joint undertaking of Technische Universität München and Helmholtz Zentrum München.