Allergy is caused by hypersensitivity of the immune system leading to a misdirected immune response. The immune system normally protects the body against harmful substances such as bacteria, viruses, and toxins. Allergy occurs when the immune system over-reacts to substances (allergens) that are generally harmless and in most people do not cause an immune response.
- 35 million Americans suffer from allergy symptoms
- 3.5 million work days are lost each year due to allergies
- 2.0 million school days are lost each year due to allergies
- $2.4 billion are spent yearly on allergy care
The first exposure to an allergen causes a mild immune response that sensitizes the immune system to the substance (triggers the immune system to recognize the substance). The second and subsequent exposure to the allergen results in symptoms. The type of symptom that develops depends on the specific allergen, the part of the body where exposure occurs, and the way the immune system reacts to the allergen. The immune system calls upon a protective antibody named immunoglobulin E or IgE to fight the allergen. Everyone has some IgE, an allergic person has an unusually large amount of IgE -too many for their own good. The oversupply of IgE antibodies attacks and engages the invading allergens. The excess of IgE binding to the allergen causes a specifc type of cell (mast cell) to release histamine and other chemical mediators that cause the symptoms of an allergic reaction. Symptoms usually are mild and are primarily annoying. However, severe reactions (anaphylaxis) can be life threatening and must be dealt with as a medical emergency.
- Runny nose
- Watery, itchy eyes
- Hives (welts on skin)
Symptoms (Severe - Life Threatening)
- Wheezing (asthma)
- Difficulty breathing
- Reduced blood pressure
The lining of the nose is most frequently effected by allergies. The word "rhinitis" means inflammation of the nose. Thus, allergic rhinitis is nasal inflammation caused by allergens. There are several signs of allergic rhinitis, which include a stuffy or runny nose, itching, and sneezing. Seasonal rhinitis refers to development of symptoms during peak times of mold and pollen usually peaking in the spring and early fall.
Allergic rhinitis requires contact with the environment. The parts of the body that are in direct contact with the allergen are affected. If the allergen contacts the nose, allergic rhinitis occurs. If pollen comes into contact with the eye, allergic conjunctivitis (inflammation of the mucous lining of a portion of the eyeball or the eyelids), which is manifested by red, itchy, watery eyes, may occur. If an individual has allergic asthma, inhaling pollen may trigger an asthma attack. People who suffer from allergic rhinitis frequently experience allergic conjunctivitis or flares of asthma at the same time. Rhinitis may be non- allergic, which means that it may have no allergic cause. Chronic nasal obstruction can be the result of anatomic obstruction in the nasal passages; although rare, it may also be caused by growths or metabolic disorders such as an under-active thyroid (a gland located in the base of the neck that produces hormones that influence growth and metabolism).
Perennial allergic rhinitis is triggered by allergens that are present year-round, such as cats, dogs, other pets, dust mites, molds, and cockroaches. Dust has many components to which people may be allergic, such as animal proteins or fungal particles. It may also contain dust mites, which are microscopic insects that live in warm, humid areas of the home such as carpets, mattresses, and upholstered furniture. Although mites cannot see, they dine on the scales of skin shed from humans. It is the fecal matter of dust mites that contains digestive enzymes to which allergic per-sons react. Ninety-nine percent of homes contain dust mites.
The part of the body contacted by the allergen will, in part, also affect symptoms. For example, allergens that are inhaled often cause nasal congestion, itchy nose/throat, mucus production, coughing, wheezing or similar symptoms. Food allergies often include, abdominal pain, cramping, or similar symptoms, although the whole body may be affected when the food is absorbed. Allergies to plants often cause skin rash. Drug allergies usually involve the whole body.
It is usually easy to identify seasonal allergic rhinitis. A history of characteristic symptoms in appropriate seasons, reports of exposure to allergens (grass pollen, ragweed pollen, cat protein, etc.), or similar symptoms among family members makes the diagnosis evident. This diagnosis may be confirmed with skin testing.
The diagnosis may be more difficult to determine for patients with perennial rhinitis since symptoms are less prominent and exposures are not seasonal. The presence of an animal that is known to frequently cause allergies can be an important clue, but allergic rhinitis resulting from other perennial allergens is harder to recognize.
Other possible causes of symptoms found in allergic rhinitis include a nasal polyp (abnormal tissue projecting into the nasal cavity) and chronic sinusitis (long-term inflammation of the nasal sinuses).
Blood tests, including those that measure total IgE (an antibody called immunoglobulin E) levels and eosinophils (a white blood cell involved in allergic response) counts, are not usually helpful.
Allergen Skin Testing
Allergen skin testing is the most important diagnostic test. It is more sensitive than blood tests for detecting IgE directed at a specific molecule. The skin test is called a RAST test or radioallergosorbent test after the laboratory procedure employed.
Skin testing usually involves two parts; each part takes about five minutes to place the tests on the skin. The tests remain in place for 15 to 20 minutes before they are interpreted. The first tests are called puncture tests during which drops of an allergen extract (a drug preparation made with the active constituents of an allergen), such as an extract of grass pollen, are placed on the forearm or sometimes the upper arm or back. The skin is then pricked or punctured through the droplet, just breaking the surface of the skin. If an allergic reaction is provoked, a small red itchy reaction like a mosquito bite occurs at the site of the prick.
After all the punctures have been evaluated, a second set of tests is sometimes done. These are called intradermal (within the substance of the skin) tests and are performed on the forearm, upper arm or occasionally the back. These are tiny superficial injections containing a diluted extract of an allergen that does not provoke a reaction on puncture testing. If these tests are positive, they also produce a reaction, similar to a small mosquito bite, at the site of injection.
Allergen skin testing allows for confirmation of the diagnosis. Additionally, with knowledge of specific positive tests, the physician can recommend which allergens to avoid and prescribe individualized medicine regimens tailored for pollen seasons or perennial sensitivities. Not all patients need allergy shots; however, for those that do, information from skin tests is used to determine the makeup of the extract received in allergy shots.
The first principle of treatment, if at all possible, is to avoid exposure to the allergens to which one is sensitive. For example, if one is allergic to grass pollen, remaining indoors between the hours of five and ten in the morning may be helpful. It is during these hours that the pollen count is the highest, particularly on dry windy days. Driving with car windows shut at times of a high pollen count is helpful. Sensitive individuals are advised to avoid mowing grass because molds and pollen may be stirred up. Raking leaves, likewise, may stir up mold. If sheets and clothes are hung to dry outside at times of a high pollen count, pollen may collect on the clothes.
In order to limit the exposure to dust mites, the home must be kept very clean. This is particularly important in the bedroom since so much time is spent there. Mites like to live in warm, dry places such as mattresses, box springs, and carpets where they can dine on flakes of skin. For this reason, allergists recommend encasing the mattress pillow and box spring in airtight allergy covers to keep mite particles from going into the air where they can be inhaled. If possible, eliminating carpets can be very helpful in the reduction of mite levels. Removing pets from the home can be emotionally difficult; however, individuals, a pet-free environment can be curative. Other methods to reduce exposure to allergens is to get a HEPA vacuum machine in the house, clean the air ducts in the home, and use a good vacuum cleaner.
Antihistamines are the most common medication for allergic rhinitis. These medications prevent histamine (a chemical released from mast cells during an allergic reaction) from attaching to its target receptor (the place Mere it attaches to evoke a response) on blood vessels, airway smooth muscle, and other cells. Thus, antihistamines prevent sneezing, itching, and some of the congestion experienced by those who suffer from allergic rhinitis. Antihistamines are available as inexpensive over-the-counter preparations, but these tend to cause drowsiness and occasionally dry mouth. The first non-sedating antihistamine, Seldane, was released in 1985. Although Seldane is no longer available, others have taken its place: Claritin, Allegra, Zyrtec (which may be slightly sedating), and Hismanal (which is very long acting and has some interactions with certain other drugs). In addition, the dosage of the newer preparations is more convenient than that of the older antihistamines; these newer preparations can be taken once or twice a day. These drugs are sometimes formulated in combination with an oral decongestant. Decongestants add to the effect of antihistamines by reducing swelling of the nasal passages. Topical (applied locally to a specific part of the body) decongestants, which can be purchased as overthe-counter nasal sprays, are not recommended for use after three or four days because they can cause significant rebound nasal congestion with prolonged use.
Steroid nasal sprays can also be prescribed and can be very effective. Steroids reduce swelling by controlling the release of fluids from vessels to surrounding tissues. They stop the influx and activity of inflammatory cells and prevent the release of some of the inflammatory molecules that are produced after an allergen binds to the IgE (an antibody called immunoglobulin E) on mast cells. The effects of the spray take at least a few days to begin while full effect may take weeks to achieve. Never the less, steroid nasal spray is the most effective and safest medication currently available. It also relieves nasal symptoms when non-allergic rhinitis is present, that is, Wien the trigger of nasal congestion is not an allergen. Steroid sprays, because they are topical, do not cause significant steroid side effects; in fact, there are very few side effects. Examples of topical steroids include Beconase, Vancenase, Nasalide, Flonase, Rhinocort, Nasonex, Nasorel, and Nasacort. Antihistamines and nasal steroids are frequently taken together.
Other medications are available, including topical antihistamines and other anti-inflammatory medications such as cromolyn. They are, however not as effective as nasal steroids with antihistamines and they have to be taken more frequently. Cromolyn is available as an over-the-counter nasal spray, but must be used three or four times a day, takes three weeks to work, and it is not as effective as nasal steroids, which presently are only available by prescription. Recently, new classes of anti-allergy medications have been marketed. They are called leukotriene inhibitors; examples include Accolate and Singulaire. Although they were first approved for asthma patients, they may have a role in allergic rhinitis as well; however, experience with these medications is still limited.
Immunotherapy (or allergy shots) is the only means of permanently altering the immune system so that an individual is less sensitive to allergens. Immunotherapy consists of injections of extracts of allergens that are identified by skin testing; thus, it is allergenspecific. This means that if one lives in the northeastern United States and receives shots for ragweed, the shots will be useful. However, if this person then moves to a ragweed-free area, the shots will be useless. Immunotherapy effectiveness is related to the potency of the extract; however, potent extracts can also cause allergic reactions to the injection. Allergic reactions are the main side effect of allergy shots; while usually self-limited, they can occasionally be severe. Over a period of 40 years, there have been approximately 40 deaths from immunotherapy in the United States. Thus, Mile very effective, immunotherapy must be administered with great caution by experienced allergists.
If one is troubled with allergic rhinitis for only one or two relatively short pollen seasons and has symptoms that are relatively mild, medications such as nasal steroids and antihistamines may be sufficient. If these medications are not sufficient, or if the allergic season is very long and severe, one might want to consider shots. One drawback of allergy shots is that they must be taken regularly, at first weekly. After approximately nine months, they can be given monthly. Usually, shots require a three to five year course and one does not see an effect before the first six to twelve months. Some patients prefer immunotherapy to long-term use of other medications. It is important to remember that shots have never been completely satisfactory for people who are allergic to animals but keep pets in the home.For additional information on allergies, visit these sites:
- About.com - Allergies
- Allergy and Asthma Network/Mothers of Asthmatics, Inc.
- Allergy Internet Resources
- American Academy of Allergy, Asthma, and Immunology
- American Association of Immunologists
- American College of Allergy, Asthma and Immunology
- American Medical Association
- AsmaNet: The International Association of Asthmology
- Clinical Immunology Society
- Community of Science
- The Food Allergy Network
- Immune Deficiency Foundation
- International Food Information Council
- Joint Council of Allergy, Asthma and Immunology
- National Institute of Allergy and Infectious Dieseases
- Northwest Asthma and Allergy Center
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