A cheat sheet for the news.
May 3 1998 3:30 AM


Doctors predict that, thanks to El Niño, the next two years will be the most allergy-ridden in history, a fitting end to what doctors call the worst century for allergies ever. The percentage of the population suffering from allergies has more than doubled over the last 40 years, according to one study. Meanwhile, as part of a dizzying parade of allergy remedies, the Food and Drug Administration has recently approved the over-the-counter sale of cromolyn sodium, a nasal spray trumpeted as the most effective nonprescription allergy combatant.


What are allergies? Who gets them? Is there any way to conquer them? Are they really more prevalent than they used to be? Why hasn't natural selection consigned this miserable condition to the dustbin of evolutionary history?

Allergies share the same etiology: The immunesystemoverreacts to the presence of harmless proteins normally not found in the body. During the first few encounters with a foreign protein (or allergen), the immune system catalogs its characteristics and tailors an antibody called immunoglobulin to purge it. Thereafter when the allergen enters the body, the immunoglobulins send signals to trigger the release of a set of nasty chemicals, most notably histamines, that destroy it. Side effects of histamines include the tightening of airways, constriction of nasal passages, release of mucus, and redness of eyes. Nobody knows how much of an allergen it takes to set off this process.

Some typologicaldistinctions: Allergies are technically different from adverse reactions to poison ivy, chemicals, and lactose, none of which involves the immune system. Allergies are also distinguishable from colds, during which the immune system combats viruses that can actually do harm.

T he most prevalent allergy is hay fever. (The Centers for Disease Control's estimate: Twenty-six million Americans suffer from the condition.) Here the immune system reacts to proteins contained in pollen, tiny airborne particles released as part of the reproductive cycle of trees, weeds, and grasses. ("Hay fever" comes down from early 19th century British farmers who misplaced blame for their ragweed allergies on the hay reaped during the fall harvest.) Other common allergies include reactions to the proteins found in food, the excrement of mites, and the saliva of some warm-blooded mammals (cats, dogs, horses). (Click for a sidebar on the myth of the nonallergenic dog.) Reactions to food afflict relatively few and, except for shellfish and peanut allergies, are most common among small children.

The consequences of allergies are usually no greater than sneezing, a stuffy nose, and itchy eyes. But if you suffer from asthma, allergies can cause an attack. And in rare cases, allergic attacks can turn into anaphylaxis, where toxic levels of histamines and other chemicals are released, causing asphyxiation, vomiting, and death. More common are infections triggered by stuffy noses. The scenario: Allergies inflame and clog a nose, precluding it from draining mucus and fluids from sinuses and ears. The fluids become a breeding ground for bacteria. (An estimated 40 percent of ear infections stem from allergies.)

Allergies are geneticallylinked. Researchers have correlated them with a single mutant gene inherited from the mother. But statistics also point to the importance of other genes that come via the father. Eighty percent of the children of two allergy-suffering parents are also allergic. With one afflicted parent, there is a 50 percent chance of inheritance; and when neither parent is an allergy sufferer, there's still a 20 percent chance.

Allergies are spread evenly across ethnicity and gender. Individuals, however, tend to experience their effects in roughly 10 year cycles. The worst period usually occurs from birth through adolescence, and then recurs in the mid-20s for another decade. But allergies can start at any time. And nobody has a clue as to why they wax and wane.


P ollen has its own patterns. In the early part of the year (March to May) trees emit pollen; from June to August, grass is the main source; from September to November, weeds are. There's no escaping pollen. Allergists say some cities (Los Angeles and Denver) are better than others (Atlanta and Washington, D.C.). But all are bad for at least a chunk of the year. Even cities such as Las Vegas and Tucson, once famed for their pure desert air, are now corrupted by trees and grass imported as part of so-called "civic improvement" projects. The lowest counts occur in coastal areas and mountains, where wind tends to blow pollen away, although pollen has been detected as far as 400 miles out to sea and two miles up. (Other useful pollen tips: During the summer, pollen counts tend to be lower before 8 a.m., after dark, and following rain.)

Every allergy season seems to be touted by the media as being the worst one on the books. (Click for a sampling of alarmist headlines from the Los Angeles Times.) And there is much dispute over whether El Niño will cause as much trouble as some allergists predict. The claim is that El Niño rains and mild temperatures will cause plants to be more fecund and produce more pollen. Also, lack of winter freezes means that mites normally killed off by the cold will survive.