Allergic rhinitis - Causes
- Risk Factors
- Lifestyle Changes
DescriptionAn in-depth report on the causes, diagnosis, treatment, and prevention of common nasal allergies.
Hay fever; Nasal congestion - allergies
The allergic process, called atopy, occurs when the body overreacts to a substance that it senses as a foreign “invader”. The immune system works continuously to protect the body from potentially dangerous intruders such as bacteria, viruses, and toxins. However, for reasons not completely understood, some people are hypersensitive to substances that are typically harmless. When the immune system inaccurately identifies these substances (allergens) as harmful, an allergic reaction and inflammatory response occurs.
- The antibody immunoglobulin E (IgE) is a key player in allergic reactions. When an allergen enters the body, the immune system produces IgE antibodies. These antibodies then attach themselves to mast cells, which are found in the nose, eyes, lungs, and digestive tract.
- The mast cells release inflammatory chemical mediators, such as histamine, that cause atopic symptoms (sneezing, coughing, wheezing). The mast cells continue to produce more inflammatory chemicals that stimulate the production of more IgE, continuing the allergic process.
There are many types of IgE antibodies, and each are associated with a specific allergen. This is why some people are allergic to cat dander, while other people are not bothered by cats buts are allergic to pollen. In allergic rhinitis, the allergic reaction begins when an allergen comes into contact with the mucus membranes in the lining of the nose.
Triggers of Seasonal Allergic Rhinitis (Hay Fever)
Seasonal allergic rhinitis occurs only during periods of intense airborne pollen or spores. It is commonly, although inaccurately, called hay fever. No fever accompanies this condition, and the allergic response is not dependent on hay. In general, triggers of seasonal allergy in the U.S. include:
- Ragweed. Ragweed is the most dominant cause of allergic rhinitis in the U.S., affecting about 75% of allergy sufferers. One plant can release 1 million pollen grains a day. Ragweed occurs everywhere in the U.S., although it is less common in western coastal states, southern Florida, northern Maine, Alaska, and Hawaii. The effects of ragweed in the northern states are first felt in middle to late August and last until the first frost. Ragweed allergies tend to be most severe before midday.
- Grasses. Grasses affect people in mid-May to late June. Grass allergies are experienced more in the late afternoon.
- Tree Pollen. Small pollen grains from certain trees usually produce symptoms in late March and early April.
- Mold Spores. Mold spores that grow on dead leaves and release spores into the air are common allergens throughout the spring, summer and fall. Mold spores may peak on dry windy afternoons or on damp or rainy days in the early morning.
Click the icon to see an animation about allergies.
Triggers of Perennial (Year-Round) Allergic Rhinitis
Allergens in the House. Allergens in the house can trigger attacks in people with year-long allergic rhinitis, called perennial rhinitis. Household allergens include:
- House dust and mites. Dust mites, specifically mite feces, are coated with enzymes that contain a powerful allergen.
- Pet dander
- Molds growing on wallpaper, house plants, carpeting, and upholstery
Other Causes of Chronic Nasal Congestion
Aging Process. The elderly are at risk for chronic rhinitis as the mucus membranes become dry with age. In addition, the cartilage supporting the nasal passages weakens, causing changes in airflow. In such cases, therapy involves avoiding possible allergens and airborne irritants as well as measures to keep the nasal passages moist. Decongestants are not helpful.
Irritative Rhinitis. Irritative rhinitis is caused by an overreaction to irritants, such as cigarette smoke, dozens of other air pollutants, strong odors, alcoholic beverages, and exposure to cold. The nasal passages become red and engorged. This reaction is not the same as an allergic reaction, although both are associated with increased numbers of white blood cells called eosinophils.
Vasomotor Rhinitis. Vasomotor rhinitis, another type of nonallergic rhinitis, is caused by oversensitive blood vessels and nerve cells in the nasal passages. It occurs in response to irritants, including smoke, environmental toxins, changes in temperature and humidity, stress, and even sexual arousal. Symptoms of vasomotor rhinitis are similar to most of those caused by allergies but eye irritation does not occur.
Blockage in the Nose from Polyps or Structural Abnormalities. A number of conditions may block the nasal passages. Surgery may be helpful for certain cases.
- Polyps. These are soft tissues that develop off stalk-like structures on the mucus membrane. They impede mucus drainage and restrict airflow. Polyps usually develop from sinus infections that cause overgrowth of the mucus membrane in the nose. They do not regress on their own and may multiply and cause considerable obstruction.
- Deviated Septum. A common structural abnormality of the nose that causes problems with air flow is a deviated septum. The septum is the inner wall of cartilage and bone that separates the two sides of the nose. When deviated, it is not straight but shifted to one side, usually the left.
- Other Causes of Blockage. Rarely, cleft palates, overgrowth of bones in the nose, or tumors cause nasal blockage.
Drugs. A number of drugs can cause rhinitis or worsen it in people with conditions such as deviated septum, allergies, or vasomotor rhinitis:
- Overuse of decongestant sprays used to treat nasal congestion can, over time (3 - 5 days) cause inflammation in the nasal passages and worsen rhinitis.
- Other medications that may cause rhinitis include oral contraceptives, hormone replacement therapy, anti-anxiety drugs (particularly alprazolam), some antidepressants, drugs used to treat erectile dysfunction, and some blood pressure medications, including beta-blockers and vasodilators.
- Sniffing cocaine damages nasal passages and can cause chronic rhinitis.
Estrogen in Women. Elevated levels of estrogen appear to increase mucus production and swelling in the nasal passages and can cause congestion. This effect is most apparent in women during pregnancy. In such cases the condition usually clears up after delivery. Oral contraceptives and hormone replacement therapies that contain estrogen have also been associated with nasal congestion in some women.
- www.aaaai.org -- American Academy of Allergy, Asthma & Immunology
- www.acaai.org -- American College of Allergy, Asthma & Immunology
- www.niaid.nih.gov -- National Institute of Allergy and Infectious Diseases
- www.njc.org -- National Jewish Medical and Research Center
- www.lungusa.org -- The American Lung Association
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- Reviewed last on: 6/1/2009
- Harvey Simon, MD, Associate Professor of Medicine, Harvard Medical School; Physician, Massachusetts General Hospital. Also reviewed by David Zieve, MD, MHA, Medical Director, A.D.A.M., Inc.