Allergies and asthma

What are allergies?

An allergy is the body's response to a substance (an allergen), which although generally not harmful in itself, can cause an immune response and reaction. This reaction, in turn, can produce uncomfortable symptoms in predisposed people. Simply put, an allergy is an overreaction of the immune system to allergens that normally cause no reaction in most individuals.

The immune system can usually distinguish between non-toxic substances in the environment and harmful microbes such as bacteria and viruses that may threaten our health. When microbes enter our bodies, the immune system sends out antibodies which attach themselves to the outer wall of those microbes and target them for destruction, leaving alone those substances it doesn't believe will harm us. In people with allergies, however, the immune system often launches an attack against allergens.

Allergies affect nearly 25% of the population, with nearly half of sufferers being children. In some cases, symptoms are mild and are more of an inconvenience than anything else. In other cases, however, allergies are not only bothersome, they complicate and handicap people's lives and are linked to other illnesses such as sinusitis and asthma. Allergic reactions can sometimes be severe and even fatal. Through proper management and education, however, allergies can be controlled and allergy sufferers can lead full and active lives.¹

What is an allergen?

An allergen is a substance that produces an allergic reaction in a predisposed person. An allergen can be almost anything.

Common allergens	Less common allergens
Dust mites Waste from cockroaches Pollen from trees and grasses Pet dander such as that from cats and dogs Feathers and down Pores from various moulds and mildew Insect bites or stings such as those of wasps and bees, yellow jackets, hornets, or fire ants Milk Eggs Seafood and shellfish Peanuts Poison ivy, sumac, or poison oak	Latex and other industrial chemicals Gluten, yeast, and some grains Chocolate Certain fruit such as strawberries or tomatoes Certain medications such as penicillin, sulfa, and antibiotics from the cephalosporin group Injected anesthetics such as procaine or lidocaine Dyes used in x-rays and other medical scans

Allergens enter the body in any number of ways. The pollens of certain trees and weeds, snow moulds, house dust, dust mite particles, and pet dander are typically inhaled through the nose and enter the lungs. Other allergens such as shellfish, nuts and fruit are ingested by mouth. Insect venom and drugs such as penicillin enter the body through injection. Allergens such as poison ivy are generally absorbed through the skin.

What happens during an allergic reaction?

During an allergic reaction, the body is simply trying to do its job by mounting an attack against what it thinks is a harmful invader. During what's known as sensitization—the time during which you're exposed to a particular allergen—the body produces antibodies. Antibodies are produced by white blood cells known as lymphocytes whose function is to fight microbes, infection and other substances invading the body. In people with allergies, these lymphocytes may produce antibodies to fight against otherwise harmless substances.²

The body produces five different types of antibodies or immunoglobulins, and each class performs a different function. Antibodies formed in response to allergens belong to the IgE class and bind to the allergen as well as to mast cells and basophils, two types of defensive cells responsible for releasing chemicals called mediators. Probably the best known mediator is histamine, which causes the sneezing, runny nose, itching, and other symptoms of an allergic reaction.³

When you suffer an allergic reaction, white blood cells known as eosinophils are attracted to the site of the reaction, causing a more intense reaction. The result is often swelling or inflammation and more widespread symptoms.⁴

What are common allergy symptoms?

Table 1. Common Allergy Symptoms

Rhinits (Hay Fever)	Food Allergy
Sneezing (often occurring in bouts) Nasal stuffiness,nasal itching, clear watery nasal discharge Itching, watering, and redness of the eyes Dark circles under the eyes Deep itching within the ear canals Fatigue Mouth breathing, scratchy throat, changes in voice Itchy palate Cough, particularly in the morning Post-nasal drip—mucus dripping from the back of the nose into the throat Sinus headache or facial pain—a feeling of pressure and discomfort at the top of the head, above the eyebrows, behind the eyes, under the eyes or on the cheeks, upper jaw, ears, or neck	Mild to moderate allergic symptoms Abdominal pain Diarrhea Vomiting Skin reaction ranging from a fine bumpy rash to large raised hives Swelling Increased eczema Itchy palate
Severe Allergy (Anaphylaxis)	Bee Stings
Swallowing and breathing difficulties caused by inflammation of the airways and swelling in the throat Coughing, wheezing, shortness of breath Dizziness Drop in blood pressure Severe allergic symptoms can be life threatening	Generalized itching, hives Swelling of the throat and tongue Difficulty breathing Dizziness Stomach cramps, nausea, or diarrhea Loss of consciousness These allergic symptoms can be life threatening

Source: Allergies. Allergy & Asthma. Certified Allergy & Asthma Consultants. (2004)

What causes allergies?

It still isn't clear just why people develop allergies. It begins with what experts call sensitization—the period during which you're exposed to an allergen. Sensitization can vary from a few weeks to several decades. Repeated exposure to a particular allergen prompts the immune system to try to fight what is otherwise a harmless substance. Most allergies become apparent during childhood, although symptoms may become dormant through adolescence to the point that some people are free of symptoms when they reach adulthood. Nevertheless, allergies can return or even have their initial onset later in life. While they seldom "outgrow" the allergies they have, adults rarely develop new allergies after the age of 40 and sometimes, reactions become less with age.⁵

Most allergies seem to be the result of the same risk factors:

Heredity

Allergies appear to run in families. Children with one allergic parent are 50 percent more likely to develop allergies. In cases where both parents have allergies, children have a 60 to 80 percent chance of developing allergies.⁶

Environment

Your surroundings, particularly early in life, play a key role in the development of allergies. If you are exposed to high levels of a particular allergen during infancy and early childhood, it's more likely you will develop allergic diseases such as hay fever and rhinits (see below). Don't forget, however, that heredity also comes into play. It's always a combination of both heredity and environment that predisposes people to allergies.⁷

Common allergic diseases
(Learn more about Types of Allergies from Aetna™ InteliHealth®.)

Table 2. Common Allergic Diseases

Condition	Characteristics
Allergic rhinitis More commonly known as hay fever	Nasal stuffiness Sneezing Nasal itching Clear nasal discharge Itchy palate Itching in the ear canals
Allergic asthma Respiratory disease caused by airway obstruction; almost always associated with allergy	Obstruction of the airways; partially reversible with medication such as inhalers or nebulizers Coughing, wheezing, shortness of breath or rapid breathing Chest tightness Occasional fatigue Slight chest pain Persistent dry cough, usually without mucus or phlegm Sleep disturbances caused by breathlessness or wheezing
Allergic conjunctivitis	Inflammation of the eyes Itchy, watery eyes Often accompanies atopic dermatitis, allergic rhinits, and asthma
Urticaria A reaction of the skin; more commonly known as hives	Itchy, raised white bumps on the skin surrounded by an area of red inflammation
Atopic dermatitis A chronic or recurrent inflammatory skin disease; more commonly known as eczema	Lesions, scaling and flaking
Contact dermatitis	Skin inflammation
Sinusitis	Inflammation of the sinuses Typically lasts longer than the common cold Fever Frontal head discomfort, facial pain Yellow or green nasal discharge
Otitis media More commonly referred to as an inner ear infection	Inflammation of the middle ear and eardrum
Food allergy	Itching or swelling of lips or tongue Tightness of the throat with hoarseness Nausea and vomiting Diarrhea Chest tightness and wheezing Itching of the eyes Decreased blood pressure or loss of consciousness and anaphylaxis
Latex allergy	Hand dermatitis, eczema and hives Sneezing and other respiratory distress Lower respiratory problems including coughing, wheezing and shortness of breath
Insect sting allergy	Pain, itching and swelling at the sting site or over a larger area and can cause anaphylaxis
Drug allergy	Allergic responses affecting any tissue or organ Occasionally anaphylaxis
Anaphylaxis* * This is a medical emergency and the most severe form of allergic reaction. Seek immediate medical attention.	Life-threatening symptoms including swelling of the throat and narrowing of the airways Sense of impending doom Generalized warmth or flush Wheezing Nausea, vomiting or abdominal pain Itchy hives throughout the body Swelling of the lips, tongue or eyes Tingling of palms, soles of feet or lips Light-headedness or dizziness Bloating and chest tightness Seizures Cardiac arrhythmia (rapid heart rate or palpitations) Shock and respiratory distress

Source: What are Allergies? Asthma and Allergy Foundation of America. (2004)

Diagnosing allergies

Sometimes, determining the cause of your allergies can be difficult. Try to pay attention to when and where you experience symptoms and to what allergens may be triggering your allergic reaction. Fortunately, there are tests that take away much of the guesswork. One of the most accurate ways to diagnose the causes of allergies is by undergoing a skin test. This test is conducted by an allergist, a physician who has been specially trained in the diagnosis, management and treatment of allergic diseases and asthma.

Before referring you to an allergist, your doctor will typically perform a physical examination and ask you about your medical history. You can expect to be asked about your past medical history, family health, current symptoms and about any factors in your home, work or school environment that may be triggering your allergic responses. If you have asthma, your doctor may recommend a pulmonary function test to assess your ability to move air into and out of your lungs. Your doctor may or may not recommend a lung x-ray, as well as cultures to determine infections. Your doctor will then typically refer you to an allergist for a skin test.⁸

During a skin test, drops of suspected allergens are placed on the skin of the arms or upper back. The skin beneath the drops is then pricked with a pin. There is usually no pain, bleeding or discomfort because only the top layer of the skin is poked. A small bump, similar to a mosquito bite, will form. Swelling or itching of the bump indicates the presence of an allergy. Swelling generally subsides within a half hour to an hour. Results are read within ten to fifteen minutes after completion of the test.⁹

In cases where the results of a skin test are unclear, the allergist may use a syringe to inject a small amount of allergen under the skin. This is known as an intradermal test.¹⁰

The allergist may also conduct what's known as a patch test in which he or she paints a small amount of allergen onto a healthy patch of skin. Alternatively, he or she may paint the allergen onto a pad or small metal disc which is placed on your skin. The skin is then coded and the area is covered for a period of 2 days, after which the allergist will check for reaction.¹¹

If you cannot undergo a skin test, your doctor will instead recommend blood tests known as RAST tests to check for the presence of IgE antibodies. RAST tests are generally reserved for those who, because of a skin condition such as eczema or because of medications, cannot take the skin test. Certain medications such as antidepressants and antihistamines interfere with skin test results.¹² Skin tests are also not used on patients suffering from anaphylaxis or on those prone to anaphylactic reactions.

To test for allergy to such foods as milk, wheat, eggs, nuts (especially peanuts) and soy, your allergist will conduct elimination or food challenge tests.

During an elimination test, suspected food allergies are elminated from your diet for a period of two to three weeks. You will be asked to keep a food diary. Both you and your doctor will watch for allergy symptoms and discuss whether they are less in the absence of food allergens. In a food challenge test, you will be given a sample of suspected food. Because certain foods may cause psychological associations, you must not know the type of food you are being given. Therefore, samples will be presented to you in capsule form, or disguised as ingredients in other foods. Once you ingest the sample, you and the allergist will then monitor any reactions. Elimination and food challenge tests are never used on patients suffering from anaphylaxis or on those prone to anaphylactic reactions.¹³

The most effective way to combat allergies and allergy symptoms is, of course, prevention. Elimination of the allergen from your diet or environment and avoidance of those things that trigger symptoms is the best way to deal with allergies. This isn't always possible, however, and in a related article, Women's Web examines the various methods of treating allergies.

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12. Diagnosing springtime allergies. Amy Norton. MSNBC.com (2004)
13. Allergy Tests. ISL Consulting Co. Yahoo! Inc. (2004)