Of all the things that can cause an allergy, pollen is one of the most common. Many of the foods, medicines, or animals that cause allergies can be avoided to a great extent. Even insects and household dust are escapable. But short of staying indoors, with the windows closed, when the pollen count is high-and even that may not help-there is no easy way to avoid airborne pollen.

What is pollen?

Plants produce tiny, microscopic -too tiny to see with the naked eye-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. Cross-pollination means that for fertilization to take place and seeds to form, pollen must be transferred from the flower of one plant to that of another of the same species. Insects do this job for certain flowering plants, while other plants rely on wind for 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 make small, light, dry pollen grains that are custom-made for wind transport.

Amazingly, scientists have collected samples of ragweed pollen 400 miles out at sea and 2 miles high in the air. Because airborne pollen can drift for many miles, it does little good to rid an area of an offending plant. In addition, most allergenic pollen comes

from plants that produce it in huge quantities. For example, a single ragweed plant can generate a million grains of pollen a day.

The type of allergens in the pollen is the main factor that determines whether the pollen 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. It is, however, a relatively rare cause of allergy because the type of allergens in pine pollen appear to make it less allergenic.

Among North American plants, weeds are the most prolific producers of allergenic pollen. Ragweed is the major culprit, but other important sources 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.

It is common to hear people say they are allergic to colorful or scented flowers like roses. In fact, only florists, gardeners, and others who have prolonged, close contact with flowers are likely to be sensitive to pollen from these plants. Most people have little contact with the large, heavy, waxy pollen grains of such 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 have 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, in the Northern Hemisphere, the farther north you go, the later the start of the pollinating period and the later the start of the allergy season.

A pollen count, 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 shown in grains of pollen per square meter of air collected over 24 hours. Pollen counts tend to be the highest early in the morning on warm, dry, breezy days and lowest during chilly, wet periods. Although the pollen count is an approximate measure that changes, it is useful as a general guide for when it may be wise to stay indoors and avoid contact with the pollen.

What is a dust mite allergy?

Dust mite allergy is an allergy to a microscopic organism that lives in the dust found in all dwellings and workplaces. House dust, as well as some house furnishings, contains microscopic mites. Dust mites are perhaps the most common cause of perennial allergic rhinitis. House dust mite allergy usually produces symptoms similar to pollen allergy and also can produce symptoms of asthma.

House dust mites, which live in bedding, upholstered furniture, and carpets, thrive in summer and die in winter. In a warm, humid house, however, they continue to thrive even in the coldest months. The particles seen floating in a shaft of sunlight include dead dust mites and their waste products. These waste products, which are proteins, actually provoke the allergic reaction.

What is house dust?

Rather than a single substance, so-called house dust is a varied mixture of potentially allergenic materials. It may contain fibers from different types of fabrics and materials such as

• Cotton lint, feathers, and other stuffing materials
• Dander from cats, dogs, and other animals
• Bacteria
• Mold and fungus spores (especially in damp areas)
• Food particles
• Bits of plants and insects
• Other allergens peculiar to an individual house or building

Cockroaches are commonly found in crowded cities and in the southern United States. Certain proteins in cockroach feces and saliva also can be found in house dust. These proteins can cause allergic reactions or trigger asthma symptoms in some people, especially children. Cockroach allergens likely play a significant role in causing asthma in many inner-city populations.

There are thousands of types of molds and yeasts in the fungus family. Yeasts are single cells that divide to form clusters. Molds are made of many cells that grow as branching threads called hyphae. Although both can probably cause allergic reactions, only a small number of molds are widely recognized offenders.

The seeds or reproductive pieces of fungi are called spores. Spores differ in size, shape, and color among types of mold. 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, tiny fungal spores, or sometimes pieces of fungi, may cause allergic rhinitis. Because they are so small, mold spores also can 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 allergy symptoms.

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, which makes 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.

Molds also like bakeries, breweries, barns, dairies, and greenhouses. Loggers, mill workers, carpenters, furniture repairers, and upholsterers often work in moldy environments.

What molds are allergenic?

Like pollens, mold spores are important airborne allergens only if they 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 in the United States. Aspergillus, Penicillium, Helminthosporium, Epicoccum, Fusarium, Mucor, Rhizopus, and Aureobasidium (Pullularia) are common as well.

There is no relationship, however, between a respiratory allergy to the mold Penicillium and an allergy to the drug penicillin, which is made from mold.

Are mold counts helpful?

Similar to pollen counts, mold counts may suggest the types and number of fungi present at a certain time and place. For several reasons, however, these counts probably cannot be used as a constant guide for daily activities.

One reason is that the number and types of spores actually present in the mold count may have changed considerably in 24 hours because weather and spore distribution are directly related. Many common allergenic molds are of the dry spore type-they release their spores during dry, windy weather. Other fungi need high humidity, fog, or dew to release their spores. Although rain washes many larger spores out of the air, it also causes some smaller spores to be propelled into the air.

In addition to the effect of weather changes during 24-hour periods on mold counts, spore populations may also differ between day and night. Dry spore types are usually released during daytime, and wet spore types are usually released at night.

Are there other mold-related disorders?

Fungi or organisms 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 allergies. 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 people, 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 small number of people with asthma, causes 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 usually treat this reaction effectively. Immunotherapy (allergy shots) is not helpful.

Allergenic-describes a substance which produces an allergic reaction

Antibody-molecule tailor-made by the immune system to lock onto and destroy specific germs

Basophils-white blood cells that contribute to inflammatory reactions

Conjunctivitis-inflammation of the lining of the eyelid, causing red-rimmed, swollen eyes, and crusting of the eyelids

Genes-units of genetic material that carry the directions a cell uses to perform a specific function

Granules-small particles; in cells the particles typically include enzymes and other chemicals

Immune system-a complex network of specialized cells, tissues, and organs that defends the body against attacks by disease-causing organisms

Inflammation-an immune system process that stops the progression of disease-causing organisms

Lymphocytes-small white blood cells which are important parts of the immune system

Mast cells-granule-containing cells found in tissue molecules-the building blocks of a cell. Some examples are proteins, fats, and carbohydrates organism-an individual living thing perennial-describes something that occurs throughout the year

Rhinitis-inflammation of the nasal passages, which can cause a runny nose sinuses-hollow air spaces located within the bones of the skull surrounding the nose

Sputum-matter ejected from the lungs and windpipe through the mouth tissues-groups of similar cells joined to perform the same function upper respiratory tract-area of the body which includes the nasal passages, mouth, and throat

NIAID supports a network of Asthma, Allergic and Immunologic Diseases Cooperative Research Centers throughout the United States. The centers encourage close coordination among scientists studying basic and clinical immunology, genetics, biochemistry, pharmacology, and environmental science. This interdisciplinary approach helps move research knowledge as quickly as possible from the lab into the hands of doctors and their allergy patients.

Educating patients and health care providers is an important tool in controlling allergic diseases. All of these research centers conduct and evaluate education programs focused on methods to control allergic diseases.

Since 1991, researchers participating in NIAID’s Inner-City Asthma Study have been examining ways to treat asthma in minority children living in inner-city environments. Asthma, a major cause of illness and hospitalizations among these children, is provoked by a number of possible factors, including allergies to airborne substances.

The success of NIAID’s model asthma program led the U.S. Centers for Disease Control and Prevention to award grants to help community-based health organizations throughout the United States implement the program.

Based on the success of the first National Cooperative Inner-City Asthma Study, NIAID and the National Institute of Environmental Health Sciences, also part of NIH, started a second cooperative multicenter study in 1996. This study recruited children with asthma, aged 4 to 11, to test the effectiveness of two interventions. One intervention uses a novel communication and doctor education system. Information about the children’s asthma severity is provided to their primary care physicians, with the intent that this information will help the doctors give the children the best care possible.

The other intervention involves educating families about reducing exposure to passive cigarette smoke and to indoor allergens, including cockroach, house dust mite, and mold. Researchers are assessing the effectiveness of both interventions by evaluating their capacity to reduce the severity of asthma in these children.

Early data show that by reducing allergen levels in children’s beds by one-third, investigators reduced by nearly one-quarter (22 percent) both the number of days the children wheezed and the number of days the children missed school.

Although several factors provoke allergic responses, scientists know that heredity plays a major role in determining who will develop an allergy. Therefore, scientists are trying to identify and describe the genes that make a person susceptible to allergic diseases.

Because researchers are becoming increasingly aware of the role of environmental factors in allergies, they are evaluating ways to control environmental exposures to allergens and pollutants to prevent allergic disease.

These studies offer the promise of improving the treatment and control of allergic diseases and the hope that one day allergic diseases will be preventable.

Scientists supported by NIAID (National Institute of Allergy and Infectious Diseases) found that, during the first years of their lives, children raised in a house with two or more dogs or cats may be less likely to develop allergic diseases as compared with children raised without pets. The striking finding here is that high pet exposure early in life appears to protect some children from not only pet allergy but also other types of common allergies, such as allergy to house dust mites, ragweed, and grass. This new finding is changing the way scientists think about pet exposure. Scientists must now figure out how pet exposure causes a general shift of the immune system away from an allergic response.

The results of this and a number of other studies suggest that bacteria carried by pets may be responsible for holding back the immune system’s allergic response. These bacteria release molecules called endotoxin. Some researchers think endotoxin is the molecule responsible for shifting the developing immune system away from responding to allergens through a class of lymphocytes called Th-2 cells. (These cells are associated with allergic reactions.) Instead, endotoxin may stimulate the immune system to block allergic reactions.

If scientists can find out exactly what it is about pets or the bacteria they carry that prevents the allergic response, they might be able to develop a new allergy treatment.

An allergist can suggest which kind of filter is best for your home. Before buying a filtering device, rent one and use it in a closed room (the bedroom, for instance) for a month or two to see whether your allergy symptoms diminish. The airflow should be sufficient to exchange the air in the room five or six times per hour. Therefore, the size and efficiency of the filtering device should be determined in part by the size of the room.

You should be wary of exaggerated claims for appliances that cannot really clean the air. Very small air cleaners cannot remove dust and pollen. No air purifier can prevent viral or bacterial diseases such as the flu, pneumonia, or tuberculosis.

Before buying an electrostatic precipitator, you should compare the machine’s ozone output with Federal standards. Ozone can irritate the noses and airways of people with allergies, especially those with asthma, and can increase their allergy symptoms. Other kinds of air filters, such as HEPA filters, do not release ozone into the air. HEPA filters, however, require adequate air flow to force air through them.

Actually, these are tips for controlling allergies to all the furry creatures you can’t help but cuddle.

If you or your child is allergic to furry pets, especially cats, the best way to avoid allergic reactions is to find them another home. If you are like most people who are attached to their pets, that is usually not a desirable option. There are ways, however, to help lower the levels of animal allergens in the air, which may reduce allergic reactions.

• Bathe your cat weekly and brush it more frequently (ideally, a non-allergic person should do this).
• Keep cats out of your bedroom.
• Remove carpets and soft furnishings, which collect animal allergens.
• Use a vacuum cleaner and room air cleaners with HEPA filters.
• Wear a face mask while house and cat cleaning.

House Dust Tips

If you have dust mite allergy, pay careful attention to dust-proofing your bedroom. The worst things to have in the bedroom are:

• Wall-to-wall carpet
• Blinds
• Down-filled blankets
• Feather pillows
• Stuffed animals
• Heating vents with forced hot air
• Dogs and cats
• Closets full of clothing

Carpets trap dust and make dust control impossible.

• Shag carpets are the worst type of carpet for people who are sensitive to dust mites.
• Vacuuming doesn’t get rid of dust mite proteins in furniture and carpeting, but redistributes them back into the room, unless the vacuum has a special HEPA (high-efficiency particulate air) filter.
• Rugs on concrete floors encourage dust mite growth.

If possible, replace wall-to-wall carpets with washable throw rugs over hardwood, tile, or linoleum floors, and wash the rugs frequently.

Reducing the amount of dust mites in your home may mean new cleaning techniques as well as some changes in furnishings to eliminate dust collectors. Water is often the secret to effective dust removal.

• Clean washable items, including throw rugs, often, using water hotter than 130 degrees Fahrenheit. Lower temperatures will not kill dust mites.
• Clean washable items at a commercial establishment that uses high water temperature, if you cannot or do not want to set water temperature in your home at 130 degrees. (There is a danger of getting scalded if the water is more than 120 degrees.)
• Dust frequently with a damp cloth or oiled mop.

If cockroaches are a problem in your home, the

U.S. Environmental Protection Agency suggests some ways to get rid of them.

• Do not leave food or garbage out.
• Store food in airtight containers.
• Clean all food crumbs or spilled liquids right away.

Try using poison baits, boric acid (for cockroaches), or traps first, before using pesticide sprays.

If you use sprays:

• Do not spray in food preparation or storage areas.
• Do not spray in areas where children play or sleep.
• Limit the spray to the infested area.
• Follow instructions on the label carefully.
• Make sure there is plenty of fresh air when you spray.
• Keep the person with allergies or asthma out of the room while spraying.

Some people report that they react to chemicals in their environments and that these allergy-like reactions seem to result from exposure to a wide variety of synthetic and natural substances. Such substances can include those found in:

• Paints
• Carpeting
• Plastics
• Perfumes
• Cigarette smoke
• Plants

Although the symptoms may resemble those of allergies, sensitivity to chemicals does not represent a true allergic reaction involving IgE and the release of histamine or other chemicals. Rather than a reaction to an allergen, it is a reaction to a chemical irritant, which may affect people with allergies more than others.

Preventing Chemical Sensitivity

Irritants such as chemicals can worsen airborne allergy symptoms, and you should avoid them as much as possible. For example, if you have pollen allergy, avoid unnecessary exposure to irritants such as insect sprays, tobacco smoke, air pollution, and fresh tar or paint during periods of high pollen levels.