Last updated: Oct 29, 2009
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Fall brings with it school days, crisp air, turning leaves—and a spike in asthma symptoms. But spring can be tough for people with asthma, too, particularly if they have a pollen allergy. And summer heat waves are notorious for sending asthmatics, particularly asthmatic children in urban areas, to the emergency room.

So why do asthma symptoms seem to get worse with every change in the weather? Although it seems confusing, there are some annual trends, as well as reasons why asthma symptoms are worse at particular times of the year.

For example, severe asthma episodes tend to peak during the autumn months, especially among children. A 2001 study that examined tens of thousands of asthma hospitalizations in Canada over a 12-year period, for instance, found that there were more than twice as many hospitalizations in October as there were in July or August. Other studies have discovered similar patterns.

However, one study conducted in Detroit found that when there was a rapid 10-degree rise in temperature or a 10% rise in humidity—as can happen in spring and summer—hospitalizations for children with asthma increased in the next day or two.

In truth, asthma symptoms can flare at any time of year due to well-known asthma triggers, such as pet dander, secondhand smoke, and exercise. But knowing the triggers that can vary by season—such as pollen, temperature, humidity, pollution, and viruses—can help people with asthma figure out if they should be stepping up their medication.

Cold air can cause an asthmatics lungs to tighten up, so you might guess that a fall peak in asthma episodes is due to cooler weather. But the patterns found in the Canadian study have also been reported in far-flung places including Hong Kong and the tropical island of Trinidad—so cold weather isnt entirely to blame.

In fact, the main culprit is believed to be cold-and-flu season, which kicks into gear once kids head back to school. Classrooms filled with runny noses, and grimy hands are breeding grounds for cold and flu viruses, which schoolchildren inevitably spread to their families.

People with asthma arent more likely to catch a virus than people without asthma, but when they do, their illness tends to be longer and more severe. Respiratory tract infections aggravate the chronic lung inflammation of asthma, which can lead to wheezing, coughing, difficulty breathing, and asthma attacks. (The flu, common cold, and other respiratory infections are responsible for about 80% of wheezing episodes in children, and about 50% of such episodes in adults.)

“The old adage, ‘If you treat a cold, it lasts a week; if you ignore it, it lasts seven days, is not true for an asthmatic,” says Bradley Chipps, MD, a pediatric pulmonologist and allergist in Sacramento, Calif. “Unless treated, the symptoms will go on for weeks sometimes.”

The flu, whether its swine flu (H1N1) or seasonal flu, can be even more perilous. A recent analysis of cases found that 28% of people hospitalized with swine flu had asthma. People with asthma are more vulnerable to complications stemming from the flu—such as pneumonia—and are more likely to be hospitalized, which is why the Centers for Disease Control and Prevention recommends that all people with asthma over six months old get the seasonal and swine flu shot. And it has to be the shot, whether its a seasonal or swine flu vaccine. (The FluMist vaccine, which is delivered via nasal spray, can cause wheezing and should be avoided by asthmatics.)

The sudden spike in asthma-related doctors appointments and ER visits among children that coincides with the start of the school year—a pattern that has been observed all around the Northern Hemisphere—is so predictable that it has come to be known as the September epidemic.

Allergens also are a problem in the fall. The ragweed season begins in late summer, but in some areas it can last well into October. This plant, which is found in the greatest quantities in the East and Midwest, is a nightmare for people with asthma who are sensitized to this allergen. Each plant produces up to a billion grains of pollen in a season, and the lightweight grains can carry on the wind for hundreds of miles.

Although fall is the peak time for a flare-up of asthma symptoms, winter weather that descends on many parts of the country in December can also pose a problem.

Cold, dry air can aggravate asthma, especially during exercise, when air is inhaled in larger amounts. “A major precipitant for wheezing is cold, dry air, especially when outside and exercising,” says Dr. Chipps. “When one looks at Olympic athletes, some of the highest instances of exercise-induced bronchospasm are in cross-country skiers, and also hockey players.” (He adds, however, that hockey-related asthma can also be caused by the chemicals used to smooth the ice.)

But people with asthma dont have to be exercising to notice the effect of cold air. For some people, even walking around outside in cold weather can cause symptoms. “Its not purely exercise induced,” says Melinda Rathkopf, MD, an allergist and immunologist who practices in Anchorage, Alaska, where winter temperatures routinely reach the teens. “For some asthmatics, cold air can be one of their triggers.”

If cold air is a trigger for you, wearing a scarf around your face will help warm and humidify the air you breathe. If that doesnt do the trick, special masks containing heat exchangers can be helpful. These masks—which essentially function like a scarf, only more so—have been shown to keep lung function from declining during exercise. Using an inhaled bronchodilator (such as albuterol) 15 to 20 minutes before exercising outdoors can also help counteract the effects of cold air.

In the wintertime, asthmatics also need to be careful about the weather inside. When windows are shut against the cold air outside and heaters and humidifiers are turned on, a different problem can arise. “By increasing the warmth and humidity inside, we contribute to indoor allergens,” says Dr. Rathkopf. “Specifically, dust mites and mold do better in high humidity.”

Another irritant found indoors is the smoke from fireplaces and wood stoves. When Dr. Rathkopf sees patients for the first time, she asks them to list their method of home heating on the intake questionnaire. “Try to minimize the use of wood-burning stoves,” she tells her patients, “and make sure that ducts and flues are clean and well ventilated.”

For asthmatics, spring means one thing above all: pollen season. Pollen is a potent allergen that, when inhaled, can inflame airways and cause asthma attacks. (Like cold-and-flu season, high pollen counts are associated with an increase in asthma-related hospital visits.)

“Pollen is a major seasonal cause of increasing asthma,” says Dr. Chipps. As with cold, dry air in the wintertime, exercising outdoors can make people with asthma especially vulnerable to asthma attacks. Fortunately, pollen concentrations are relatively predictable. “Pollen counts are the highest between about 4 a.m. and 10 a.m. every day, so if youre going to be exercising during the pollen season, youre better off doing it later in the day,” he says.

The pollen season is a one-two punch. Trees begin to release pollen around March (depending on where you live), and just when youre recovering from the tree pollen, grass pollen peaks in May and June. “Parents come in and say that their kid gets a cold at the end of every school year—but its probably tree allergies,” says Dr. Rathkopf. “Sneezing, itching, and runny nose are often mistaken as a cold.”

In warmer climates, pollen is in the air for much of the year. In colder climates with distinct seasons that experience deep freezes in the winter, the pollen season is often shorter yet much more intense, according to Dr. Rathkopf.

Although spring lacks the extreme weather of winter and summer, the seasons unpredictable weather can still cause problems. The Detroit study of children with asthma, which was published in the Annals of Allergy, Asthma & Immunology, suggested that changes in temperature and humidity—rather than the levels themselves—are responsible for triggering asthma exacerbations. The study, which controlled for levels of pollutants and allergens in the air (which are affected by weather), found that a 10-degree increase in temperature and a 10% change in humidity were associated with a slight uptick in asthma-related emergency room visits.

“The reason we did this project was because of something we saw in clinic,” says Alan Baptist, MD, the lead author of the study and the director of the University of Michigan asthma program. “We often ask patients, ‘What triggers your asthma? And a lot of times, patients and parents of small children with asthma will say, ‘When the weather changes.”

Summer usually provides some relief for people with asthma. The worst of the spring pollen season is over, and cold-and-flu season has yet to begin. Asthma episodes tend to be lowest in the summer months, in fact, but that doesnt mean they cant still cause problems for some asthmatics. Some people with asthma react poorly to heat and humidity, though this is far from universal and varies widely from patient to patient. “Some patients do horribly in very high-humidity climates, and some arent bothered at all,” says Dr. Chipps. “Its clearly not a one-size-fits-all thing.”

Summer weather also tends to coincide with poorer air quality, especially in dense urban areas. Traffic-related pollution and sunlight can combine to promote the production of ozone—a powerful asthma trigger—and the stagnant, humid air of heat waves traps particulate matter and other pollutants, causing them to hang in the air and become more concentrated. These bad air days make people with asthma more vulnerable to breathing problems and asthma attacks.

“We tell our patients to watch for days of high heat and humidity, and to be especially mindful on ozone action days,” says Dr. Baptist. He encourages his patients to use a peak flow meter to monitor their lung function on these sweltering days.

Thunderstorms—a fixture of summer—are yet another asthma trigger. The gusty winds that accompany thunderstorms stir up mold and fungal spores, and rainwater breaks up pollen grains into hundreds of microscopic pieces, both of which spell trouble for asthmatics. Thunderstorms often cause a spike in asthma-related ER visits. “Often we get very high levels of mold during the time around thunderstorms, and we see increases in [emergency department] visits at that time,” says Dr. Chipps.

Toward the end of summer, pollen becomes a problem again, as the ragweed season kicks off in mid-August. In many places, concentrations of an airborne fungus, Alternaria, also peak in August and September. These allergens continue into the fall, and before you know it, its cold-and-flu season again.