- 10 Common Allergy Triggers Slideshow Pictures
- Take the Quiz on Allergies
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- Patient Comments: Hay Fever - Symptoms
- Patient Comments: Hay Fever - Treatment
- Find a local Asthma & Allergy Specialist in your town
- Hay fever facts
- What is hay fever? What are hay fever symptoms and signs?
- Why does an allergic reaction occur?
- What causes allergic rhinitis?
- What are risk factors for allergic rhinitis?
- When and where does allergic rhinitis occur?
- Is allergic rhinitis contagious?
- How is allergic rhinitis diagnosed, and how are allergies identified?
- What is the treatment for allergies?
- What is the prognosis of allergic rhinitis?
- Is it possible to prevent allergic rhinitis?
Quick GuideAllergy Pictures Slideshow: 10 Common Allergy Triggers
Why does an allergic reaction occur?
An allergic reaction occurs when the immune system attacks a usually harmless substance called an allergen that gains access to the body. The immune system calls upon a protective substance called immunoglobulin E (IgE) antibodies to fight these invading allergic substances or allergens. Even though everyone has some IgE, an allergic person has an unusually large amount of IgE. This army of IgE antibodies attacks and engages the invading army of allergic substances of allergens.
Specialized cells called mast cells also participate in the allergic reaction. Mast cells release a variety of chemicals into the tissues and blood, one of which is known as histamine. These chemicals frequently cause allergic reactions. These chemicals are very irritating and cause itching, swelling, and fluid leaking from cells. Through various mechanisms, these allergic chemicals can cause muscle spasm and can lead to lung and throat tightening as is found in asthma and loss of voice.
What causes allergic rhinitis?
Any substance can cause an allergy if exposed to an allergic person in the right way. But for all practical purposes and with few exceptions, allergic rhinitis is caused by proteins. Commonly, allergic rhinitis is a result of an allergic person coming in contact several times with protein from plants. Many trees, grasses, and weeds produce extremely small, light, dry protein particles called pollen. This pollen is spread by the wind and is inhaled. These pollen particles are usually the male sex cells of the plant and are smaller than the tip of a pin or less than 40 microns in diameter.
Even though pollen is usually invisible in the air, pollen is a potent stimulator of allergy. Pollen lodges in the nasal lining tissues (mucus membranes) and other parts of the respiratory tract, where it initiates the allergic response. Up to 7.8% of American adults suffer from allergic rhinitis. Approximately one in four people with allergic rhinitis also has asthma.