Allergic conditions: determinants

Allergic conditions arise from an abnormal response to foreign substances (allergens) such as grass, weed and tree pollens, house dust, fungal spores, animal products, foods, drugs and chemicals. To some extent, the risk of allergic conditions is related to the level of exposure of the population to allergens. The factors that determine the risk of an abnormal response to allergens are less well understood, although there is likely to be a genetic component.