An allergen is any substance that the body mistakenly perceives as a threat, triggering a specific chain of events called an allergic cascade. The immune system protects the body from harmful foreign substances. Sometimes, it mistakenly identifies a harmless allergen as a threat. The resulting allergic reaction causes symptoms, such as sneezing, coughing, runny nose, sore throat, diarrhea, vomiting, itching and hives. More severe reactions can result in lower blood pressure, difficulty breathing and, in some cases, death.

Most allergies fall into one or more of the following categories:

• Airborne substance allergies (e.g., pollen, dust, mold)
• Food allergies
• Animal or insect allergies
• Cosmetic or chemical allergies
• Drug or medication allergies (over-the-counter or prescription)

Allergy management usually includes the use of medications to prevent or relieve allergy symptoms. These include:

• Antihistamines (prevent the release of symptom-causing chemicals into the body)
  
• Decongestants (reduce nasal and chest congestion)
  
• Corticosteroids and NSAIDs (reduce inflammation)
  
• Bronchodilators (open breathing passages)
  
• Other medications (e.g., leukotriene modifiers, mast cell stabilizers)

The most effective way to treat an allergy is to avoid the allergen. However, this can be difficult with certain allergens. For instance, people with food allergies need to avoid not only the problem food, but all products that contain that food or components of that food. Individuals with allergic rhinitis (hay fever) often find it difficult to avoid the airborne pollens that are present in the outdoor air at some times of the year.

Depending on the allergen, there are tools to help people avoid contact with an allergen. These include:

• Allergy index. A measure of the number of people affected by pollen in a certain region. Based on a scale of 1 to 10, it takes into account both the amount of pollen present in the air and how sensitive most people are to the pollen types present.
  
  
• Pollen and mold report. Describes the current amount of airborne allergens present in the air. Results are presented in grains per cubic meter of air.
  
  
• Food labels. A list all of a food’s ingredients on the packaging of the food, required in the United States by the Food and Drug Administration. This is a very valuable resource for individuals with food allergies. Because of the complexity of today’s food manufacturing and production, food labels are often the only way to tell if a food includes allergy-causing ingredients.

Asthma, a condition in which the airways become blocked or narrowed, can be exacerbated by contact with allergens. Asthma attacks are triggered by many different environmental factors including allergens, exercise and cold air. An allergic response to allergens such as pollen, dander or certain foods can cause the airways to inflame and constrict, leading to an asthma attack. Individuals having an asthma attack often experience shortness of breath, breathing difficulty and cough.