The Learning Center

 

What are allergies ?

 

Understanding the immune system

Self and Non-self

The heart of the immune system is the ability to distinguish between self and non-self. Virtually every body cell carries molecules that identify it as self. The body's immune defenses do not normally attack tissues that carry a self-marker. When immune defenders encounter cells or organisms carrying molecules that say "foreign," the immune troops move quickly to eliminate the intruders. Any substance capable of triggering an immune response is called an antigen. Antigens can be a virus, a bacterium, a fungus, or a parasite. An antigen announces its foreignness by means of characteristic shapes called epitopes, which protrude from its surface.

Keeping Out Foreigners

The immune system stockpiles a tremendous arsenal of cells. In order to have room to match millions of possible foreign invaders, just a few of each type of antibody are stored. When an antigen appears, those matched cells multiply into a full-scale army. Antibodies belong to a family of large molecules known as immunoglobulins. Immunoglobulins are proteins, made up of chains of amino acids. Scientists have identified nine chemically distinct classes of human immunoglobulins (Ig). Each type plays a different role in the immune defense strategy. IgE, which under normally occurs only in trace amounts, is the villain in allergic reactions. Each IgE antibody is specific; one reacts against oak pollen, another against ragweed.

OOPS! False Alarm

The first time an allergy-prone person is exposed to an allergen, he or she makes large amounts of the corresponding IgE antibody. These IgE molecules attach to the surfaces of cells in the body. When an IgE antibody encounters its specific allergen, it signals the body to begin powerful chemical warfare. These chemicals include histamine, heparin, eosinophils, and neutrophils.

Your Nose Knows these Symptoms…….

Do You?

It’s really warfare, but to you, it may appear as one or more of the following symptoms:

  • Sneezing often accompanied by a runny or clogged nose
  • Coughing
  • Postnasal drip
  • Itching eyes, nose, or 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)
  • Watering eyes
  • Conjunctivitis (inflammation of the membrane that lines the eyelids, causing red-rimmed, swollen eyes, and crusting of the eyelids).

First The Diagnosis

People with allergy symptoms, such as the runny nose of allergic rhinitis, may at first suspect they have a cold--but the "cold" lingers on. It is important to see a doctor about any respiratory illness that lasts longer than a week or two. When it appears that the symptoms are caused by an allergy, you should see a physician who understands the diagnosis and treatment of allergies. If the patient's medical history indicates that the symptoms recur at the same time each year, the physician will work under the theory that a seasonal allergen (like pollen) is involved. Properly trained specialists recognize the patterns of potential allergens common during local seasons and the association between these patterns and symptoms. The medical history suggests which allergens are the likely culprits. The doctor also will examine the mucous membranes, which often appear swollen and pale or bluish in persons with allergic conditions.

Skin Tests

Doctors use skin tests to determine whether a patient has IgE antibodies in the skin that react to a specific allergen. The doctor use diluted extracts from allergens such as dust mites, pollens, or molds commonly found in the local area. The extract of each kind of allergen is injected under the patient's skin or is applied to a tiny scratch or puncture made on the patient's arm or back. Skin tests are one way of measuring the level of IgE antibody in a patient. With a positive reaction, a small, raised, reddened area (called a wheal) with a surrounding flush (called a flare) will appear at the test site. The size of the wheal can give the physician an important diagnostic clue, but a positive reaction does not prove that particular pollen is the cause of a patient's symptoms. Although such a reaction indicates that IgE antibody to a specific allergen is present in the skin, respiratory symptoms do not necessarily result.

Blood Tests

Although skin testing is the most sensitive and least costly way to identify allergies in patients, some patients such as those with widespread skin conditions like eczema should not be tested using that method. There are other diagnostic tests that use a blood sample from the patient to detect levels of IgE antibody to a particular allergen. One such blood test is called the RAST (radioallergosorbent test), which can be performed when eczema is present or if a patient has taken medications that interferes with skin testing.

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What is asthma ?

Asthma is a reversible obstructive lung disease, caused by an increased reaction of the airways to various stimuli. It is a chronic condition with acute exacerbations. In this country, there are approximately 28 million asthmatics; nearly one third of them (8.6 million) are children under 18 years of age. Asthma can be a life-threatening disease if not properly managed. Asthma is characterized by excessive sensitivity of the lungs to various stimuli. Asthma breathing problems usually happen in "episodes" or "attacks".  An asthma episode is a series of events that result in narrowed airways. These include: swelling of the lining , tighting of muscles, and increased secretion of mucus in the airway. The narrowed airway is responsible for the difficulty in breathing with the familiar "wheeze".Triggers range from viral infection to allergies, to irritating gases and particles in the air. Each person  reacts differently to the factors that may trigger asthma, including some respiratory infections; colds; allergic reactions to pollen, mold, animal dander, feathers, dust food1 and cockroaches; vigorous exercise; exposure to cold air or sudden temperature change; cigarette smoke; excitement, and stress.

Asthma therapy includes efforts to reduce the underlying inflammation and to relieve or prevent symptomatic airway narrowing. Such efforts should lead to reduction in airway hyperresponsiveness and help prevent irreversible airway obstruction

The two classes of medications used to treat asthma are bronchodilators and anti-inflammatory agents. 

  • Mti-inflammatory agents interrupt the development of bronchial inflammation and have a prophylactic or preventive action. They may also modulate or terminate ongoing inflammatory reaction in the airways. These agents include corticosteriods, cromolyn sodium or cromolyn-like compounds, and other anti-inflammatory compounds.

  • Bronchodilators act principally to dilate the airways by relaxing bronchial smooth muscle. They include bet~adrenergic agonists, methylxanthines, and anticholinergics

Asthma is the leading serious chronic illness among children. Most children have mild to moderate problems and their illness can be controlled by treatment at home or in the doctor's office. For some children the illness becomes a formidable problem causing numerous visits to the hospital emergency room and multiple hospitalizations

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Animal Dander Allergy

Household pets are the most common source of allergic reactions to animals. Many people think that pet allergy is provoked by the fur of cats and dogs. But researchers have found that the major allergens are proteins secreted by oil glands in the animals' skin and shed in dander as well as proteins in the saliva, which sticks to the fur when the animal licks itself. People have always said that when it comes to allergies, cats are worse than dogs. We now know that it is because cats lick themselves more than dogs, thereby spreading the allergens. In addition, cats may be held more and spend more time in the house, close to humans. Urine is also a source of allergy-causing proteins. When the substance carrying the proteins dries, the proteins can then float into the air. Some rodents, such as guinea pigs and gerbils, have become increasingly popular as household pets. They, too, can cause allergic reactions in some people, as can mice and rats. Urine is the major source of allergens from these animals. Allergies to animals can take two years or more to develop and may not subside until six months or more after ending contact with the animal. Carpet and furniture are a reservoir for pet allergens, and the allergens can remain in them for four to six weeks. In addition, these allergens can stay in household air for months after the animal has been removed. Therefore, it is wise for people with an animal allergy to check with the landlord or previous owner to find out if furry pets had lived previously on the premises.

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House Dust & Dust Mite Allergy

An allergy to dust found in houses is perhaps the most common cause of perennial allergic rhinitis. House dust allergy usually produces symptoms similar to pollen allergy.

What is house dust?

Rather than a single substance, house dust is a varied mixture of potentially allergenic materials. The particles seen floating in a shaft of sunlight may contain fibers from different types of fabrics; cotton lint, feathers, and other stuffing materials; bacteria; mold and fungus spores (especially in damp areas); food particles; bits of plants and insects; and other allergens peculiar to an individual home. Dust also may contain microscopic mites. These mites also live in bedding, upholstered furniture, and carpets. Ordinarily, they would thrive in summer and die in winter. However, in a warm, humid house, they continue to thrive even in the coldest months. These waste products, which are proteins, actually provoke the allergic reaction. House dust mite allergy is the major year-round allergy in the world, though ragweed is more prevalent in the United States. Waste products of cockroaches are also an important cause of allergy symptoms from household allergens, particularly in some urban areas of the United States.

What are Dust Mites?

Dust mites are tiny animals you cannot see. Every home has dust mites. They feed on skin flakes and are found in mattresses, pillows, carpets, upholstered furniture, bedcovers, clothes, stuffed toys, and fabric or other fabric-covered items. Body parts and feces of dust mites can trigger allergic reactions in sensitive individuals. The presence of dust mites in a home are in no way an indication of the sanitary conditions in the home.

 

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Mold Allergy

Along with pollens from trees, grasses, and weeds, molds are an important cause of seasonal allergic rhinitis. People allergic to molds may have symptoms from spring to late fall. The mold season often peaks from July to late summer. Unlike pollens, molds may persist after the first killing frost. Some can grow at subfreezing temperatures, but most become dormant. Snow cover lowers the outdoor mold count dramatically but does not kill molds. After the spring thaw, molds thrive on the vegetation that has been killed by the winter cold. In the warmest areas of the United States, however, molds thrive all year and can cause year-round (perennial) allergic problems. In addition, molds growing indoors can cause perennial allergic rhinitis even in the coldest climates.

What is mold?

There are thousands of types of molds and yeast, the two groups of plants in the fungus family. Yeasts are single cells that divide to form clusters. Molds consist of many cells that grow as branching threads called hyphae. Although both groups can probably cause allergic reactions, only a small number of molds are widely recognized offenders. The seeds or reproductive particles of fungi are called spores. They differ in size, shape, and color among species. Each spore that germinates can give rise to new mold growth, which in turn can produce millions of spores.

What is mold allergy?

When inhaled, microscopic fungal spores or, sometimes, fragments of fungi may cause allergic rhinitis. Because they are so small, mold spores may evade the protective mechanisms of the nose and upper respiratory tract to reach the lungs. In a small number of people, symptoms of mold allergy may be brought on or worsened by eating certain foods, such as cheeses, processed with fungi. Occasionally, mushrooms, dried fruits, and foods containing yeast, soy sauce, or vinegar will produce allergic symptoms. There is no known relationship, however, between a respiratory allergy to the mold Penicillium and an allergy to the drug penicillin, made from the mold.

Where do molds grow?

Molds can be found wherever there is moisture, oxygen, and a source of the few other chemicals they need. In the fall they grow on rotting logs and fallen leaves, especially in moist, shady areas. In gardens, they can be found in compost piles and on certain grasses and weeds. Some molds attach to grains such as wheat, oats, barley, and corn, making farms; grain bins, and silos likely places to find mold.

Hot spots of mold growth in the home include damp basements and closets, bathrooms (especially shower stalls), places where fresh food is stored, refrigerator drip trays, house plants, air conditioners, humidifiers, garbage pails, mattresses, upholstered furniture, and old foam rubber pillows. Bakeries, breweries, barns, dairies, and greenhouses are favorite places for molds to grow. Loggers, mill workers, carpenters, furniture repairers, and upholsterers often work in moldy environments.

Which molds are allergenic?

Like pollens, mold spores are airborne allergens that are abundant, easily carried by air currents, and allergenic in their chemical makeup. Found almost everywhere, mold spores in some areas are so numerous they often outnumber the pollens in the air. Fortunately, however, only a few dozen different types are significant allergens. In general, Alternaria and Cladosporium (Hormodendrum) are the molds most commonly found both indoors and outdoors throughout the United States. Aspergillus, Penicillium, Helminthosporium, Epicoccum, Fusarium, Mucor, Rhizopus, and Aureobasidium (Pullularia) are also common.

Are there other mold-related disorders?

Fungi or microorganisms related to them may cause other health problems similar to allergic diseases. Some kinds of Aspergillus may cause several different illnesses, including both infections and allergy. These fungi may lodge in the airways or a distant part of the lung and grow until they form a compact sphere known as a "fungus ball." In people with lung damage or serious underlying illnesses, Aspergillus may grasp the opportunity to invade the lungs or the whole body. In some individuals, exposure to these fungi also can lead to asthma or to a lung disease resembling severe inflammatory asthma called allergic bronchopulmonary aspergillosis. This latter condition, which occurs only in a minority of people with asthma, is characterized by wheezing, low-grade fever, and coughing up of brown-flecked masses or mucus plugs. Skin testing, blood tests, X-rays, and examination of the sputum for fungi can help establish the diagnosis. Corticosteroid drugs are usually effective in treating this reaction; immunotherapy (allergy shots) is not helpful.

Indoor Air Regulations and Mold

Standards or Threshold Limit Values (TLVs) for airborne concentrations of mold, or mold spores, have not been set. Currently, there are no EPA regulations or standards for airborne mold contaminants.

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Multiple Chemical Sensitivity

Synthetic chemicals are all around us. They're in the products we use, in the clothes we wear, in the food we eat, in the air we breathe at work. Because chemicals are everywhere in the environment, it's not possible to escape exposure. No wonder, then, that many people have become sensitized to the chemicals around them. For some people the sensitization is not too serious a problem. They may have what appears to be a minor allergy to one or more chemicals. Chemical sensitivity is not a true allergic reaction because IgE is not actually present. Other people are much more seriously affected. They may feel tired all the time, and suffer from mental confusion, breathing problems, sore muscles, and a weakened immune system. Such people suffer from a condition referred to as Multiple Chemical Sensitivity (MCS).

What is Multiple Chemical Sensitivity?

MCS is a disorder triggered by exposures to chemicals in the environment. Individuals with MCS can have symptoms from chemical exposures at concentrations far below the levels tolerated by most people. Symptoms occur in more than one organ system in the body, such as the nervous system and the lungs. Exposure may be from the air, from food or water, or through skin contact. The symptoms may look like an allergy because they tend to come and go with exposures, though some people's reactions may be delayed. As MCS gets worse, reactions become more severe and increasingly chronic, often affecting more bodily functions. No single widely available medical test can explain symptoms. In the early stages of MCS, repeat exposure to the substance or substances that caused the initial health effects provokes a reaction. After a time, it takes less and less exposure to this or related chemicals to cause symptoms. As the body breaks down, an ever-increasing number of chemicals, including some unrelated to the initial exposure, are found to trigger a reaction. MCS affects the overall health and feeling of well being of those with the disorder. It typically impairs many bodily functions including the nervous system and digestion. Each individual affected by MCS has a unique set of health problems. A chemically sensitive person may also have other preexisting health conditions. Many affected people experience a number of symptoms, in relation to their chemical exposures. MCS may result from a single massive exposure to one or more toxic substance or repeated exposures to low doses. People with MCS may become partially or totally disabled for several years or for life.

Treatment

MCS is difficult for physicians to define and diagnose. There is no single set of symptoms which fit together as neither a syndrome, nor a single diagnostic test for MCS. Instead, physicians should take a complete patient history that includes environmental and occupational exposures, and act as detectives in diagnosing this problematic condition. After the onset of MCS, a person's health generally continues to deteriorate. It may only begin to improve once the chemical sensitivity condition is uncovered. While a number of treatments may help improve the baseline health status for some patients, at the present time, there is no single "cure" except avoidance.

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Pollen Allergy

Pollen

Each spring, summer, and fall, tiny particles are released from trees, weeds, and grasses. These particles, known as pollen, hitch rides on currents of air. Although their mission is to fertilize parts of other plants, many never reach their targets. Instead, they enter human noses and throats, triggering a type of seasonal allergic rhinitis called pollen allergy, which many people know as hay fever or rose fever (depending on the season in which the symptoms occur). Of all the things that can cause an allergy, pollen is one of the most widespread. People with pollen allergies often develop sensitivities to other troublemakers that are present all year, such as dust mites. Year-round airborne allergens cause perennial allergic rhinitis, as distinguished from seasonal allergic rhinitis.

What is pollen?

Plants produce microscopic round or oval pollen grains to reproduce. In some species, the plant uses the pollen from its own flowers to fertilize itself. Other types must be cross-pollinated; that is, pollen must be transferred from the flower of one plant to that of another plant of the same species. Insects do this job for certain flowering plants, while other plants rely on wind transport. The types of pollen that most commonly cause allergic reactions are produced by the plain-looking plants (trees, grasses, and weeds) that do not have showy flowers. These plants manufacture small, light, dry pollen granules that are custom-made for wind transport.

Where is pollen most common?

Most allergenic pollen comes from plants that produce it in huge quantities. A single ragweed plant can generate a million grains of pollen a day. Samples of ragweed pollen have been collected 400 miles out at sea and 2 miles high in the air. The chemical makeup of pollen is the factor that determines whether it is likely to cause hay fever. For example, pine tree pollen is produced in large amounts by a common tree, which would make it a good candidate for causing allergy. The chemical composition of pine pollen, however, appears to make it less allergenic than other basic types. Because pine pollen is heavy, it tends to fall straight down and does not scatter. Therefore, it rarely reaches human noses. Among North American plants, weeds are the most prolific producers of allergenic pollen. Ragweed is the major culprit, but others of importance are sagebrush, redroot pigweed, lamb's quarters, Russian thistle (tumbleweed), and English plantain. Grasses and trees, too, are important sources of allergenic pollens. Although more than 1,000 species of grass grow in North America, only a few produce highly allergenic pollen. These include timothy grass, Kentucky bluegrass, Johnson grass, Bermuda grass, redtop grass, orchard grass, and sweet vernal grass. Trees that produce allergenic pollen include oak, ash, elm, hickory, pecan, box elder, and mountain cedar. It is common to hear people say that they are allergic to colorful or scented flowers. In fact, only florists, gardeners, and others who have prolonged, close contact with flowers are likely to become sensitized to pollen from these plants. Most people have little contact with the large, heavy, waxy pollen grains of many flowering plants because this type of pollen is not carried by wind but by insects such as butterflies and bees.

When do plants make pollen?

One of the most obvious features of pollen allergy is its seasonal nature--people experience it symptoms only when the pollen grains to which they are allergic are in the air. Each plant has a pollinating period that is more or less the same from year to year. Exactly when a plant starts to pollinate seems to depend on the relative length of night and day--and therefore on geographical location--rather than on the weather. (On the other hand, weather conditions during pollination can affect the amount of pollen produced and distributed in a specific year.) Thus, the farther North you go, the later the pollinating period and the later the allergy season. A pollen count, which is familiar to many people from local weather reports, is a measure of how much pollen is in the air. This count represents the concentration of all the pollen (or of one particular type, like ragweed) in the air in a certain area at a specific time. It is expressed in grains of pollen per square meter of air collected over 24 hours. Pollen counts tend to be highest early in the morning on warm, dry, breezy days and lowest during chilly, wet periods. Although a pollen count is an approximate and fluctuating measure, it is useful as a general guide for when it is advisable to stay indoors and avoid contact with the pollen.

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