Fighting Seasonal Allergies

by National Institute of Health

Sometimes it's hard to know whether you're suffering from allergies or a string of colds. Their symptoms - like sneezing, coughing and a runny nose - are similar. If you have these symptoms every spring or fall, or all through the growing season, it's a good bet you've got seasonal allergies, or hay fever. Doctors call this type of allergy "seasonal allergic rhinitis". Whatever its name, it can make you absolutely miserable.

The National Institute of Allergy and Infectious Diseases (NIAID) estimates that the number of people suffering from allergic rhinitis may be as high as 35 million. Allergic rhinitis may not seem dangerous in itself, but it can play a role in other diseases like asthma, a chronic and potentially fatal lung disease affecting approximately 15 million Americans, and sinusitis, an infection in the hollow air spaces of the skull surrounding the nose that affects approximately 38 million Americans.

There is no cure for allergy, but there are ways to control its symptoms and, hopefully, to prevent it from triggering more serious conditions like asthma and sinusitis.

The Allergic Response

Whether allergic rhinitis strikes by season or lasts all year long, it is essentially the same disease. Seasonal allergic rhinitis is frequently caused by pollen released into the air by trees, grasses and weeds as part of their reproductive cycle. Molds can cause similar allergic symptoms. They release tiny spores that ride on the wind to establish the mold in new places. Whether pollens or spores, when these airborne allergens (the name for allergy-causing compounds) get into your nose and your eyes, they can cause allergies.

But what exactly is an allergy? Everybody is exposed to these pollens and spores, but only some develop allergies to them. An allergy comes about when the immune system, which is there to protect us from microbial invaders like viruses and bacteria, reacts to a normally harmless substance. Specialized cells of the immune system - known as B cells - manufacture molecules called antibodies to bind very specifically to different foreign invaders (see figure). There are five different classes of antibodies, each with its own function. IgA antibodies, for example, are found in saliva, nasal secretions and tears. IgG antibodies are the major type in the blood. Another group, IgE, causes the symptoms of allergies.

Scientists aren't actually sure what protective role IgE antibodies normally have. Laboratory mice without IgE seem perfectly normal. So do people with little detectable IgE. "What else does IgE do in the system?" Dr. Dean Metcalfe, Chief of NIAID's Laboratory of Allergic Diseases, asks. "I don't think anybody knows. The speculation is that IgE may be involved in host defenses against parasites." But since most clinical trials are conducted in countries where there are few diseases caused by parasites, it's been difficult for scientists to test this theory.

What scientists do know is that IgE antibodies attach to the surfaces of two types of immune system cells: mast cells and basophils. When these IgE encounter the allergen they were manufactured to recognize - for example, on a pollen grain or a mold spore - they attach like a key in a lock and trigger the mast cells and basophils to release the little packets of chemicals they contain. Those chemicals include histamine and other compounds that cause local inflammation, leading to the symptoms that you know as an allergy: sneezing, coughing, a runny or clogged nose, postnasal drip, and itchy eyes and throat.

"There is nothing intrinsically wrong with mast cells or basophils," Dr. Metcalfe explains. But when B cells make IgE to some environmental antigen that most people don't respond to, the mast cells and basophils are activated when you don't want them to be, and you have an allergy.

Scientists think that some people simply have a genetic tendency to develop allergies. "The genes themselves have not yet been identified," Dr. Marshall Plaut, Chief of NIAID's Allergic Mechanisms Section, says. "But there's an impressive amount of work that's been done to identify regions in chromosomes where there appear to be genes associated with allergy."

Recognizing an Allergy

Sometimes it's obvious you have allergic rhinitis. If you have symptoms like a runny nose and itchy eyes all year round, it's a good bet your condition is caused by allergies. The culprit may be something indoors like dust mites in your bedding or carpet, or mold in the shower.

Many allergies are more acute and temporary. "Maybe you walk into somebody's house, they have three cats and suddenly your eyes itch, or your nose itches or your nose runs or you start to wheeze," Dr. Metcalfe says. "Pretty clearly, that's an allergy. The exposure to something that triggers these allergic reactions - and that's reproducible - is often the first sign to people they have an allergy."

But it's not always easy to tell if you have allergies. Dr. Metcalfe says, "Let's say that somebody's sitting around and it's, say, February, and they say, 'Gee I think I'm getting a cold.' But maybe they're developing a tree allergy, because the tree pollen may be coming out in February or March in their area. Well, sometimes it's pretty hard for someone to determine whether it's a cold or a transient seasonal allergy."

Your doctor can help you sort out whether you have allergies, but it's difficult for him or her to make a diagnosis without your help. You can play an important role by keeping track of when and where you get symptoms. "The mucus membranes look a little different, but it's not enough to make a perfectly clear diagnosis," Dr. Plaut says. "The history of your symptoms is usually much stronger evidence than simply looking. It's often the duration of symptoms; people do not have colds that last more than two weeks."

Look at your local pollen and mold counts and see if high numbers match up with when you get your symptoms. Peak seasons for pollens and molds differ depending on where you live, but many local newspapers, TV and radio stations now track levels of molds and pollens daily. The National Allergy Bureau of the American Academy of Allergy, Asthma and Immunology (not associated with NIH), which reports current pollen and mold spore levels to the media, maintains a web site you can check yourself at http://www.aaaai.org/nab/. As a general guide, tree pollen allergies strike in late winter to early spring, grass allergies can strike from spring through summer, and ragweed typically strikes in the fall.

Ultimately, your doctor may send you to an allergy specialist, or allergist, for blood or skin tests to see if your body is making IgE against particular allergens. But keep in mind that even these tests can't be used alone for a diagnosis. Dr. Metcalfe says, "You cannot send your blood away to some laboratory in another state, get a readout of what you have IgE to, and then say you're allergic to the following twelve things. Those are not absolute diagnostic tests. They're just used to show that you have the potential and if the history agrees, then the physician and the patient may together reach the diagnosis."

That's because IgE antibodies are necessary for an allergy to develop, but they're not the whole story. "The basic abnormality in allergic diseases is that people make IgE antibodies to specific allergens, and if they didn't make those IgE antibodies they wouldn't be allergic," Dr. Plaut explains. "But that's not to say that everybody who makes IgE antibody has major symptoms." In common allergies, he says, there is a wide range of IgE antibody levels.

So even with such sophisticated tools, you still play an important role in helping your doctor figure out if you have allergies, and what is causing them.

About the Author

NIH is the nation's medical research agency - making important medical discoveries that improve health and save lives. The National Institutes of Health (NIH), a part of the U.S. Department of Health and Human Services, is the primary Federal agency for conducting and supporting medical research.