Most allergies appear before age 20. They commonly develop in children and possibly even in the womb, but allergies can occur in any person at any age, and they are virtually never outgrown. Asthma may persist in adults while nasal allergies tend to decline in old age. While specific allergies are not inherited, your risk of developing allergies is greatly increased if members of your family are allergic.

Practically any substance which normally causes no reaction at all can become an allergy-causing nuisance. Exposure can make allergic people too ill to function normally, forcing them to miss work, school and other important activities. Even if their symptoms are not serious, allergies can make their lives miserable.