Health Encyclopedia - Diseases and Conditions

• A
• B
• C
• D
• E
• F
• G
• H
• I
• J
• K
• L
• M
• N
• O
• P
• R
• S
• T
• U
• V
• W
• Y

Allergies

• Definition of Allergies
• Description of Allergies
• Causes and Risk Factors of Allergies
• Symptoms of Allergies
• Diagnosis of Allergies
• Treatment of Allergies
• What Questions To Ask Your Doctor About Allergies

Definition of Allergies

Allergies are abnormal reactions to ordinarily harmless substances. The sensitizing substances, called allergens, may be inhaled, swallowed, or come into contact with the skin.

Allergens that most frequently cause problems are: pollens, mold spores, house dust mites, animal danders, foods, insect bites or stings, plants, insect spores, latex rubber, viruses, bacteria, medications and environmental conditions (such as cold temperatures). Allergic reactions can occur in one area, such as sneezing or a skin rash or sneezing, or may include more than one symptom.

Description of Allergies

Normally, the body learns to defend itself through experience - by encountering, battling and remembering one enemy after another. For decades, medical science has taken advantage of this ability by using vaccination to create immunity - the immunologic "memory" of a disease. Allergic reactions occur after the immune system mistakenly learns to recognize innocent foreign substances (allergens) as potentially harmful.

The following story illustrates how an allergy can develop:

Over a field of ragweed plants floats an invisible cloud of pollen grains, soon carried by the wind into a nearby town. The pollen is inhaled by a child whose body has never been exposed to this substance before.

Because of some genetic predisposing factor, this child's immune system overreacts and produces large numbers of IgE antibodies, all specially designed to respond to ragweed pollen. Several of the antibodies attach themselves to cells in the child's nasal passages and upper respiratory tract.

These cells (known as mast cells) contain strong chemicals called mediators, the best-known of which is histamine.

Later, when the child inhales the same kind of pollen again, proteins from the pollen bind in a lock-and-key fashion to the specially designed antibodies on the surface of the mast cells. This sets off an explosion of sorts, as the mediators burst from inside the mast cells, destroying the pollen and also damaging surrounding tissues. The results are sneezing, a stuffy head, sniffling, stuffed-up head and red, watery eyes - well-known hallmarks of allergies.

---

---

Causes and Risk Factors of Allergies

The fundamental cause of allergy is still not known. The problem has a tendency to run in families. An allergic individual is more likely to have relatives who are allergic than would be expected on the basis of chance, but non-hereditary factors apparently play a part as well. Evidence of this is the fact that infants who are breast-fed are less likely to develop allergies than bottle-fed babies.

The reason an individual becomes sensitive to some substances and not to others remains a mystery.

Individuals can be affected by a variety of allergic diseases. The most common allergic diseases are allergic rhinitis, non-allergic rhinitis, asthma, allergic dermatitis, contact dermatitis and urticaria. (Allergic rhinitis is the most common of the allergic diseases and the main focus of this health profile. More comprehensive information about the other conditions may be found under that particular term.)

Allergic rhinitis is a general term used to apply to anyone who has allergy-based symptoms. Allergic rhinitis can be a seasonal problem (commonly known as "hay fever" or pollen allergy) or a year-round problem (commonly known as perennial allergic rhinitis). Hay fever or seasonal allergic rhinitis is caused by allergy to pollens of trees, grasses, weeds or mold spores. Perennial allergic rhinitis is caused by house dust, animal danders, mold and some foods.

Asthma is caused by intrinsic and extrinsic (inhaled) factors. Intrinsic factors are pollens, dust, dust mites, animal fur, animal dander or feathers. Extrinsic factors are respiratory infections; a cough, cold or bronchitis; exercise and tobacco smoke or other air pollutants, and can be caused by an allergy to a particular food or medication.

Eczema, also known as allergic dermatitis or atopic dermatitis, can be caused by foods or other allergens.

Contact dermatitis is caused by exposure to certain plants (such as poison ivy or poison oak), cosmetics, medications, metals and chemicals.

Urticaria, also known as "hives", is caused by allergy to foods, such as nuts, tomatoes, shellfish and berries. Hives can also be caused by medications, such as aspirin and penicillin.

Symptoms of Allergies

The signs and symptoms of allergic rhinitis are:

• sneezing, often accompanied by a runny or clogged nose
• coughing and postnasal drip
• itching eyes, nose and throat
• allergic shiners (dark circles under the eyes caused by increased blood flow near the sinuses)
• the "allergic salute" (in a child, persistent upward rubbing of the nose that causes a crease mark on the nose)
• watery eyes
• conjunctivitis (an inflammation of the membrane that lines the eyelids, causing red-rimmed, swollen eyes and crusting of the eyelids)

The signs and symptoms of asthma are:

• a feeling of tightness in the chest
• breathlessness
• coughing
• difficulty inhaling and exhaling
• noisy breathing ("wheezing")

The signs and symptoms of eczema, contact dermatitis and urticaria are:

• red, itchy skin
• inflamed skin
• welts (in hives)

WARNING: If a person is experiencing more severe symptoms than what is listed above, they may be in anaphylactic shock.

Anaphylactic shock is a medical emergency which is an acute systemic (affecting the whole body) allergic reaction. It occurs after exposure to an antigen (allergen) to which a person was previously sensitized.

The signs and symptoms of anaphylactic shock include the general symptoms of a common allergic reaction, PLUS:

• rapidly worsening symptoms (or previously severe reactions to this allergen)
• swelling of tissues such as lips or joints
• wheezing, noisy breathing or shortness of breath
• rash or redness of the skin
• loss of consciousness
• anxiety
• itching of the skin
• headache
• nausea and vomiting
• abdominal cramps
• diarrhea
• low blood pressure
• convulsions
• itching of the mouth and throat
• hoarseness, change of voice
• chest pain and tightness
• a feeling of warmth and flushing
• cramping of the uterus
• the feeling of having to urinate
• sweating
• confusion

Allergens more commonly associated with anaphylactic shock are: certain insect venoms; drugs such as penicillin; and foods like fish, peanuts, nuts, eggs and seeds.

Call 911 if any of these symptoms occur with an allergic reaction. If not treated promptly and properly, anaphylaxis can result in death. Fortunately, the tendency to have such serious reactions is rare.

Treatment of anaphylactic shock is first to inject adrenaline (epinephrine) to constrict the small blood vessels, raise the blood pressure and dilate the airway. This may be followed by injection of antihistamines and/or steroids, plus the use of life-support systems.

Diagnosis of Allergies

Besides a thorough medical history, the doctor will perform a number of skin tests and/or a blood test called radioallergosorbent test (RAST).

There are three skin tests used to evaluate and diagnose allergies, the prick method, the intradermal test and the patch test:

• The prick method is the most common type of skin test. This test is done by placing a drop of allergen extract on the skin on the back and passing a needle through the extract and making a tiny puncture in the skin. If allergic to the allergen a hive will appear at the site of the puncture within about 15 minutes. The doctor can perform multiple prick tests with varying allergen extracts simultaneously.
• The intradermal test uses a syringe to inject the allergen extract into the top layer of skin in the upper arm, which raises a small bubble on the skin surface. Like the prick method, a hive will appear indicating an allergic reaction.
• The patch test can be used to look for substances that might be causing contact dermatitis. A suspected allergen is placed on the skin and covered with a bandage for 48 hours. If the patient is allergic, the skin will become red and peel.

When skin testing is not feasible, as in the case of people with eczema and other skin conditions, RAST (blood test) is used. Diagnostic tests can be done by using a blood sample from a patient to detect the levels of IgE antibody to a particular allergen.

Treatment of Allergies

There are three general approaches to the treatment of allergic diseases such as allergic rhinitis: avoidance of the allergen, medication to relieve symptoms and allergy shots.

Avoidance

• Wear a pollen mask when mowing the grass or housecleaning.
• Stay indoors in the morning (when the pollen count is at its highest) and on windy days.
• Read and understand food labels (for people with food allergies).
• Keep windows and doors closed during heavy pollination seasons.
• Use the air conditioner in the house and car.
• Rid the home of indoor plants and other sources of mildew.
• Don't allow dander-producing animals in the house.
• Change feather pillows, woolen blankets and clothing to cotton or synthetic materials.
• Enclose mattress, box springs and pillows in plastic barrier cloth.
• Wash sheets, mattress pad and blankets weekly in hot water (at least 130F).
• Remove carpets and upholstered furniture (drastic measure).
• Use acaricide (a chemical that kills house-dust mites) or a tannic acid solution (solution that neutralizes the allergen in mite droppings).
• Use air filters.
• Use a dehumidifier.

Medication

When avoidance or control of an allergen isn't possible, medications may be necessary. Common allergy medications are:

• Decongestants: administered via spray or orally to unclog nasal passages. Examples of spray decongestants are oxymetazoline (Afrin) and phenylephrine (Vicks Sinex). Other medications or brands may be recommended by your doctor or pharmacist.

  Oral decongestants include pseudoephedrine (Sudafed) and combinations of decongestants and analgesics.

• Steroid nasal sprays: administered via spray to mute the inflammatory response. Medications include fluticonase (Flonase), mometasone (Nasonex), triamcinolone (Nasocort), and beclomethasone (Beconase, Vancenase).
• Antihistamines: drugs that block the action of histamine, which is responsible for allergic symptoms. Short-acting antihistamines, which are generally over-the-counter (non-prescription), often relieve mild to moderate symptoms, but can cause drowsiness. A pediatrician should be consulted before using these medicines in children, as they may affect learning. One formerly prescription medication, loratadine (Claritin), is now available over the counter. It does NOT tend to cause drowsiness or affect learning in children. Longer-acting antihistamines cause less drowsiness, can be equally effective, and usually do not interfere with learning. These medications, which require a prescription, include fexofenadine (Allegra), and cetirizine (Zyrtec). Other nonprescription antihistamines include diphenhydramine (Benadryl), chlorpheniramine maleate (Chlor-Trimeton, Coricidin) and clemastine (Tavist). New to the market, and available by prescription only, is an antihistamine nasal spray called azelastine (Astelin).
• Cromoglycate (Nalcrom)or related agents: administered mostly as eyedrops or nasal sprays to help prevent attacks.

Immunotherapy

When avoidance, environmental control measures and medications fail to control allergy symptoms, the doctor may suggest allergy immunotherapy ("allergy shots"). Immunotherapy involves the injections of allergen extracts to "desensitize" the person.

Typically, the treatment begins with injections of a weal solution of allergen given one to five times a week, with the strength gradually increasing. When the maximum dose is reached, maintenance injections are given at increasing intervals until the patient receives injections only once a month.

It may take up to six months or so to show results. It usually takes about three to four years for the patient to be free of symptoms.

Treatment of Asthma

Asthma treatment involves two major groups of medications - anti-inflammatories (corticosteroids) and bronchodilators. Anti-inflammatories reduce inflammation and lessen the risk of acute asthma attacks. They may be inhaled via a metered dose inhaler (MDI) or taken orally via pill/tablet or liquid form. The inhaled corticosteroids include fluticasone (Flovent), budesonide (Pulmicort), flunisolide (AeroBid), triamcinolone (Azmacort) and beclomethasone (Beclovent and Vaceril). The oral corticosteroids (pill/tablet form) include prednisone (Deltasone, Meticorten or Paracort), methylprednisolone (Medrol) and prednisolone (Delta Cortef and Sterane). The oral corticosteroids for children include are Pedipred and Prelone.

A new class of anti-inflammatories called leukotriene inhibitors, including zafirlukast (Accolate) and zileuton (Zyflo), work by inhibiting fatty acids that mediate inflammation from binding to smooth muscle cells lining the airways. These drugs prevent rather than reduce symptoms and are intended for long-term use.

Other inhaled anti-inflammatory drugs include cromolyn sodium (Intal) and nedrocromil (Tilade).

Bronchodilators increase the diameter of the air passages and ease the flow to and from the lungs. The short-acting bronchodilators are metaproterenol (Alupent, Metaprel), ephedrine, terbutaline (Brethaire) and albuterol (Proventil, Ventolin). The long-acting bronchodilators include salmeterol (Serevent), metaproterenol (Alupent), and theophylline (Aerolate, Bronkodyl, Slo-phyllin, and Theo-Dur). Serevent and Alupent are inhaled and theophylline is taken orally.

Advair combines fluticasone and salmeterol as a preventive medication that reduces both inflammation and airway constriction.

Treatment of Eczema, Contact Dermatitis and Urticaria

Eczema (allergic dermatitis) and contact dermatitis (such as with poison oak or ivy) can be treated with cold compresses for 30 minutes 3 times a day, and/or corticosteroid creams or ointments (topical steroids). Hives (urticaria) can be relieved by applying calamine lotion or by taking type H1 antihistamine drugs. More severe cases of hives may require corticosteroid drugs.

What Questions To Ask Your Doctor About Allergies

Should skin testing be done?

Do you recommend nasal sprays or drops? What are the side effects?

What other medications are recommended to relieve the symptoms of allergies?

Do you recommend desensitization with injections?

What measures can be taken minimize the reactions?

Do allergic rhinitis (hayfever) reactions lead to sinus infections or asthma or any other condition?

Are foods causing the allergies?

Am I at risk for anaphylactic shock? If so, what precautions can I take?