The Reasons We're Sneezin

As millions continue to scratch and sniff, scientists grapple with persistent allergy threats and discover some nasty new ones

  • Ellen Hale
  • Apr 01, 1991
Except during the dead of winter, Anne Fitzgerald seldom dares to dawdle outdoors. Her Windows remain shut tight, even on glorious spring days. Day and night, at home and on the road, air conditioners filter the air she breathes.

It's not that she doesn't like nature. Problem is, nature apparently doesn't like her.

From early spring through late fall—from the first tree blossom until autumn's liberating frost—nature pummels the 41year-old Maryland resident with a relentless airborne assault that renders her headachy, itchy, sneezy, sniffily and all-around miserable. "It's not any one thing," she says. "It seems to be just everything, all the time."

Indoors, the threat to Fitzgerald and millions of other susceptible Americans is no less insidious. New studies show that a host of unlikely culprits—house dust, mold and even cockroaches—are sending out a barrage of microscopic particles that float through the air and into our lungs. In the body these allergens, as they are called, can set off a chain of reactions that lead to allergic rhinitis, resulting in the itchy eyes, runny nose, coughing and sneezing many people call hay fever. Worse, doctors say the irksome, disruptive and sometimes fatal medical problem of allergies is on the rise.

Researchers are constantly discovering allergy-causing substances in places they never thought of looking before. If that weren't bad news enough, known allergens are also becoming a greater nuisance, in this country and elsewhere, largely because of changing agricultural practices, habitat destruction and increasing pollution, which appears to exacerbate the allergens' harmful effects.

"Worldwide, allergies are increasing," says John A. Anderson, head of the Division of Allergy and Clinical Immunology at Henry Ford Hospital in Detroit. "Countries are more industrialized and more polluted. More people are moving into cities, and there are more irritants in the air that work with allergy sensitivity."

According to the National Institutes of Health, about 40 million Americans suffer from allergies. Although most do not react as severely as Anne Fitzgerald, many are afflicted with several types of allergies, sometimes all at once. Another 15 million Americans have asthma, the severe and sometimes fatal breathing disorder marked by blockage of the bronchial airways; recent studies suggest that most asthma is caused by allergies. Airborne particles are by far the most common causes of allergies, though insect bites, food, drugs and other substances also trigger allergic reactions.

Despite the misery allergies bring, only in the past few decades have medical scientists begun to regard them as a serious health problem. Allergies kill far fewer people than heart disease or cancer, yet they constitute the costliest medical complaint in the country. One of ten visits to the doctor involves allergies, which are the major cause of missed school days for children. And Americans spend some $5 billion a year to treat asthma.

Grim statistics notwithstanding, scientists say the horizon is brightening. With the development of new drugs and treatments, physicians are able to give more patients greater relief from allergic symptoms. Medical researchers working on the forefront of technology are also getting closer to creating new therapies that could, in effect, cure people of their hay fever—which, incidentally, often has nothing to do with hay. (In the 1800s, apparently, farmers in England blamed their wheezing and sneezing on the hay they were cutting instead of the other grasses and weeds blooming at the time.)

Virtually any blooming plant can cause an allergic reaction, but people usually come in contact with pollen only from plants that depend on the wind to transport the particles for fertilization and reproduction. Once inhaled, the allergen provokes the body's immune system to attack it with a protein called IgE, shorthand for immunoglobulin E. Tissue cells then release chemicals such as histamine and prostaglandin, which cause sneezing, watery eyes and a runny nose.

In North America, the single most offensive pollen comes from ragweed, a pervasive weed that blooms from late summer through autumn. One reason ragweed is so devilish is that a single plant can generate a million grains of pollen a day. The lightweight grains also stay aloft longer than those of most other plants and can travel great distances: Ragweed pollen has been found 400 miles out at sea and at altitudes as high as 2 miles.

But thousands of other wind-pollinated plants can also trigger allergies. In the spring, trees tend to create the most trouble, says Joan Nowicke, curator in the botany department of the Smithsonian National Museum of Natural History in Washington, D.C. Box elder, oak, birch and maple are among the peskiest. Later in spring the grasses begin to flower, and in summer come marsh elder, thistle and the late-flowering grasses.

While most major allergens have been identified, scientists recently discovered a new one: Parthenium hysterophorus, or Santa Maria feverfew. This opportunistic weed proliferates in the southeastern coastal United States and often is found growing in sidewalk cracks. As many as 2 million Americans may have been blaming their allergies on ragweed when the real culprit is feverfew. "We just weren't recognizing it as an airborne source of pollen," says Walter H. Lewis, a medicinal botanist at Washington University in St. Louis, who describes feverfew as "one of the last major allergens to be discovered."

In a study published in 1989, Lewis and H. James Wedner, chief of clinical allergy and immunology at Washington University School of Medicine, reported that fully one-third of people susceptible to fall allergies who live in the states around the Gulf of Mexico may be vulnerable to Santa Maria feverfew. The study of 580 allergy patients revealed that 8 percent of them were exclusively allergic to the plant, while 30 percent were sensitive to both feverfew and ragweed.

While feverfew represents a major discovery, scientists recently have also identified some other, less pervasive allergens. Three years ago, researchers found large amounts of a gangly weed with white blossoms and a red stem called Parietaria judaica, or pellitory-of-the-wall, in the San Francisco Bay area. While the plant had long been considered a major cause of allergies in Europe, doctors had overlooked it in this country until a frantic patient brought a bagful into the office of an allergist in San Francisco to prove her complaints were real.

If most sources of pollen-activated allergies are known, other types of airborne allergens are only now being recognized for their serious allergenic effects. Among the latest suspects: the fungi. Primitive organisms, fungi include everything from mushrooms in the forest to the mold on a slice of bread.

Spores cast from fungi are the least well-known of airborne allergens, perhaps because they are so frustrating to study. "Pollen is easy to sample. It's very large and you can look at a grain and see what it is," says University of Michigan researcher Harriet Burge. "Fungal spores are much smaller, and they can't be collected as easily."

Scientists previously thought only members of the Fungi imperfecti group caused allergies. Recently, however, they discovered that another group, the Basidiomycetes, are also to blame. Supermarket mushrooms belong to the latter group, though they generally are harvested before they have time to produce allergenic spores. As much as 15 percent of the nation's population may be allergic to mold.

Making these sensitivities particularly troubling is that molds often thrive indoors: "Basement walls, windowsills—anyplace there's water," says Burge, pointing out that mold can lurk under carpeting and behind wallpaper. Fungal spores often cause asthma, probably because the spores are small enough to penetrate into the lungs.

Scientists are also beginning to understand the significance of other, seemingly unlikely sources of allergies. Last year, for example, U.S. Department of Agriculture entomologists proclaimed cockroaches a threat to human health.

From 10 to 15 million people in this country may suffer runny noses, skin irritation and breathing troubles when exposed to the proteins found in cockroach exoskeletons, feces and blood. Because cockroach parts may linger for years behind walls, in attics and other out-of-the-way places long after the insects have been eradicated, even homes free of live roaches may harbor the allergens for years.

According to USDA entomologist Richard J. Brenner, allergy to cockroaches can lead to shock and, in extremely rare cases, even death. An allergy to one type of cockroach can cause sensitivity to another, says Brenner, adding that it could possibly trigger allergies to other arthropods—lobsters, for example.

Brenner's research at the USDA's insect laboratory in Florida shows that cockroaches tend to avoid drafts, suggesting that airtight houses are ideal habitats for the pests. Roaches also seem to prefer areas with high humidity, meaning that a dehumidifier may help drive them away.

Other indoor allergens are equally troublesome. One of the most common allergens—certainly the most difficult to deal with—involves the country's favorite household pet: the cat. One-third of all homes in the United States own at least one cat, and proteins in feline saliva have been found to bring on hay fever. Cats constantly groom themselves with their tongues. The saliva dries on their fur and gets into the air, where it can be inhaled by people. It is light, flaky and sticky—the perfect allergen, says Anderson.

One solution is to give kitty a bath. In a study reported last year, Wedner and a team of researchers bathed ten adult cats once a month for ten minutes in lukewarm, distilled water. The scientists found that a monthly washing significantly reduces the amount of the protein Fel D1, the major allergy-causing substance in cat dander. A tannic acid solution sprayed on carpets and upholstery also can reduce the levels of the cat allergen protein as well as other allergens such as dust mites and pollen.

Dust mites are a particularly worrisome cause of allergies because they are so prevalent, especially in places with year-round humid climates. These hairy, microscopic monsters with serrated claws inhabit virtually every house in many parts of the world. They thrive on sheets, blankets and mattresses, where they feast on flakes of shed human skin. According to one estimate, the average double bed hosts some two million of the scavengers.

Though they don't bite, dust mites can cause trouble when they or their feces are catapulted into the air we breathe—which happens just about every time a bed is made, for example. The bugs actually are more pernicious dead than alive. After they die, usually in colder months, their shells linger, breaking into smaller pieces. These lightweight fragments float in the air, where they can enter a person's respiratory tract and spark an allergic reaction. A study last summer revealed that exposure early in life to dust mites is an important cause of childhood asthma. (It is difficult to eliminate every trace of dust mites, though vacuuming floors and mattresses helps.)

Given the sea of allergens in which the average American already swims, it would seem impossible to make things worse. But that's just what we are doing. For instance, because of habitat destruction, Santa Maria feverfew has overtaken ragweed as the major allergen in Texas and is also spreading rapidly throughout Florida.

Bulldozers clear land of existing plants, wiping out competition and making way for opportunistic weeds like feverfew "It's growing like gangbusters because so many people are moving there, and the environment and habitat are being opened up," says Lewis. "The weed just takes over." For the same reason, ragweed is now found in most parts of the United States.

Changing agricultural practices, too, have encouraged the spread of airborne allergens. In fact, says Harriet Burge, agriculture is probably the single largest source of mold spores. Farmers generally no longer plow under such crops as corn and soybeans immediately after harvest as they once did. Instead, they allow them to rot first, often not turning them over until spring. The result is a field awash in mold. "Later, the harvester comes through and puts billions and billions of spores in the air," says Burge.

Indoors, the problem can be just as bad. As Americans strive to make their homes more energy-efficient, they create allergy havens. Humidity, which experts say should remain at 50 percent for comfort, may climb as high as 75 percent in some homes, making them ideal for molds.

Airtight houses trap dust mites as well. Infestation with these bugs has always been rare in Sweden, but a study reported last August shows house dust allergies on the rise in Swedish children. Researchers traced the illnesses to super-insulated homes where leaks had been plugged, preventing a mix of outdoor air and allowing humidity to increase.

Scientists say chemical pollutants in the air probably worsen allergies, though few studies have been done and no one understands the precise mechanism. Burge suggests that molecules of these pollutants somehow attach themselves to windborne allergens and exacerbate their impact on susceptible people. Indeed, recent research in New York, Massachusetts and Ontario, Canada, shows a higher incidence of hospitalization for respiratory ailments in summer months when acid concentrations in the air are highest.

There is hope, however, and strong new ammunition against nature's air raid. For instance, two medications released in the past few years, Seldane and Hismanal, promise relief of allergy symptoms without causing drowsiness, says John Anderson. Late last year, British researchers discovered a natural chemical they claimed could be used as an all-purpose allergy vaccine.

Many patients already get help from immunotherapy, which involves injecting extracts of allergens to build a patient's resistance. Now James Wedner and other researchers are working on a type of immunotherapy that would target the exact proteins within a substance that cause allergic reactions. Such treatments, however, are probably a decade away.

Until sure-fire remedies are available, allergy sufferers must fend off the assault as best they can. They can kill the roaches, scrub the house, crank up the air conditioner and put out the cat.

But forget moving away from allergens. "You can't escape," says Anderson. "They're everywhere."

Ellen Hale covers environmental issues for Gannett News Services and, alas, is allergic to strawberries and lobster.

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