Environmental Allergy (Allergic Rhinitis) and Hay Fever Medications

10 Common Allergy Triggers Slideshow Take the Quiz on Allergies Nasal Allergy Relief Slideshow

• What Are Allergies?
• What Are the Risks of Allergies?
• What Medical Treatments Are Used for Allergies and Hay Fever?
• Antihistamines
• Decongestants
• Anticholinergic Nasal Sprays
• Corticosteroid Nasal Sprays
• Antiallergy Eyedrops
• Leukotriene Inhibitors
• Mast Cell Inhibitors
• For More Information
• Synonyms and Keywords
• Authors and Editors

What Are Allergies?

An allergic reaction occurs when the immune system responds in an abnormal fashion to a substance that is foreign to the body. The immune system normally protects the body from harmful agents like bacteria and toxins. The body's abnormal response to a substance that is usually harmless (called an allergen) is called a hypersensitivity reaction, or an allergic reaction. Generally, these reactions are due to interactions between the allergen and the family of proteins, IgE (immunoglobulin E), resulting in activation of cells in the body called mast cells and basophils. These cells release chemical messengers in the body that cause the symptoms of an allergic reaction.

Many substances in the environment can become allergens but only in genetically susceptible people. Dust mites, molds, animal hair or danders, pollens, medications, foods, and insect venoms are examples of common allergens. Reactions may be in the nose (hay fever), eyes (conjunctivitis), chest (asthma), or it can be systemic (anaphylaxis), meaning it can involve the entire body.

Allergic rhinitis is an inflammation of the nasal membranes (along with membranes of the eyes, eustachian tubes, middle ear, sinuses, and throat) due to an allergic reaction. It is the most common cause of inflammation in the nose (rhinitis). Approximately 20% of the U.S. population is believed to suffer from allergic rhinitis.