"Atopy" is when there are changes in some of the genes a person is born with ("genetic inheritance"). These genetic changes make their body produce more Immunoglobulin E (IgE), a type of "antibody". They are also more sensitive to things things like chemicals, smoke and dust ("environmental antigens"). This "hypersensitivity" means they are more sensitive or "allergic" to things in the environment than people who do not have these changes in their genes and are not hypersensitive or "allergic".