Allergies are the result of inappropriate immune responses to normally harmless substances. Allergy symptoms vary widely, from the sneezing, watery eyes, and nasal congestion of mild "hay fever" to severe rashes, swelling, and shock. Asthma is a chronic inflammation of the lungs that airborne allergens can trigger in susceptible people; tobacco smoke, air pollution, viral respiratory infections, or strenuous exercise can also contribute.
Allergies are the sixth leading cause of chronic disease in the United States and cost the healthcare system $18 billion annually.19 About half of all Americans test positive for at least 1 of the 10 most common allergens:20
Food allergy occurs in 6 to 8 percent of children age 6 years or younger and in 2 percent of adults.21 Common food allergens include:
The prevalence of asthma is also high. For reasons that are still unclear, the prevalence of both allergy and asthma in the United States is increasing.
*cited from www3.niaid.nih.gov