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You have taken extensive measures toeliminate asthma triggers from yourhome. You have given away the cat,ripped up the carpet, replaced plushcurtains with vertical blinds, and cov-ered every mattress and pillow. Nowyou’re about to step outside the asth-ma-friendly environment you’ve cre-ated. Could more trouble be waitingjust outside the door? If you are oneof the many people with asthma whofinds his or her symptoms worsenedby weather conditions, the answermay be yes.

People with asthma have reactiveairways, which means the airways intheir lungs respond when they comein contact with certain stimuli—including substances or conditions inthe environment—creating symptomsthat include wheezing, coughing, andshortness of breath. Unfortunately forthese people, common weather condi-tions can provide a number of thesestimuli, although they often can bedifficult to track and assess.

“Weather and weather changes canaffect asthma,” explains Mark H.Moss, MD, an assistant professor atthe University of Wisconsin MedicalSchool. “There are specific aspects ofweather [and its effect on asthma]that have been well studied but otheraspects that are not well studied norclearly understood. These effects,however, are commonly expressed bypatients.”

Seasons and WeatherAmong the scientists studying the

relationship between weather andasthma exacerbation are medicalphysicians and climatologists. Dr.Laurence Kalkstein, professor andassociate director of the Center forClimatic Research at the Universityof Delaware, is one of a group of sci-entists studying the effect of weatheron human health, including asthma.“For people with asthma, the effectof weather is not the same in all sea-sons; it varies,” says Kalkstein.

“Generally, we find that, during thefall season, weather seems to have anoticeable effect. After certainweather conditions, the number ofasthma-related emergency room vis-its goes up dramatically. Those con-ditions include the first cold air massto come in the fall.”

In analyzing trends in asthma-related hospital visits, Kalkstein evalu-ated all seasons. “The summer showsa rather flat and low number of asth-matic hospital visits—the lowest allyear. The weather in summer is leastvariable, so even though there may bea lot of airborne allergens around andpollution levels can be high, the sum-mer doesn’t show really high peaks inasthma. In the spring, we do see someday-to-day variability, but it’s notnearly as extreme as in the fall.”

Moss points out that part of theproblem with identifying whichweather elements trigger asthmasymptoms is the complexity of theproblem. Take rain as an example.

Gretchen W. Cook

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“For people with allergic asthmawho are sensitive to tree, grass, orweed pollen, they may have moretrouble during peak pollen seasons,usually spring or fall,” says Moss.“However, rain can affect the impactof pollen season in a good or badway. In some cases, rain can be badin the sense that it helps everythinggrow—including pollen-generatingplants. But then if you have a slow,prolonged rain, it can wash thepollen out of the air and reducepollen counts.”

Despite the complexity of weath-er’s effects on asthma, certain weath-er patterns are either known or sus-pected to cause problems for peoplewith asthma.

Cold AirCold air is a major trigger of asthma,and its effect has been studied wide-ly. “We’ve shown cold air to be avery powerful challenge to the asth-matic patient in the laboratory,”explains Philip Silkoff, MD, clinicaldirector of adult ambulatory pul-monary services at National JewishMedical and Research Center. “If Itake an asthmatic and I make him orher inhale cold, dry air, that individ-ual will, in some cases, develop bron-chospasms and wheezing, which canbe quite dramatic.”

One group of people who shouldbe especially vigilant about cold, dryweather are people with exercise-induced asthma. “There are certain

sports, such as hockey, figure skating,and cross-country skiing, where this isa particular problem,” says Moss.“Also, runners can have more troublecontrolling asthma during wintermonths when the air is dry and cold.”

Hot, Humid AirIf moving to the tropics to escapecold, dry winter air was in yourplans, think again. “Many of ourpatients report that in the summer,on very humid days, they feel anincreasing shortness of breath,” saysSilkoff. “Exactly why warm air orvery humid air causes asthma symp-toms is not quite clear. Molds, whichare a common asthma trigger, cer-tainly grow in warm, humid weather.Despite our lack of understanding,however, it’s definitely somethingreported by patients.”

WindWindy days during pollen seasonscause an increase in asthma flares.When it is windy, pollen and moldspores become airborne, where theyare more likely to be breathed in byan allergic person and trigger asthmasymptoms.

ThunderstormsA relationship seems to exist betweenthunderstorms and an increase inreported asthma symptoms. In aBritish study published in the June1997 issue of the Journal ofEpidemiology and Community Health,researchers tracked calls made to anafter-hours phone service for generalpractitioner physicians. They trackedcalls on two nights—one when therewere widespread thunderstorms andone when the weather was clear.They found, in the geographic areasaffected by the storms, 488 asthma-related calls were made on the nightof the storms compared with only 48such calls from those same areas onthe clear night.

“The mechanism behind this[association between thunderstormsand asthma] appears to be the winds

When Weather Triggers Asthma

• Limit exertion in cold, dry air.• Wear a scarf or mask over nose and mouth when outside during periods

of very cold weather.• Keep a fast-acting relief medication (bronchodilator) handy. In cold

weather, ensure the inhaler is kept as warm as possible to ensureeffectiveness.

• Stay indoors with windows closed on peak pollen days, especially on windy days during pollen season.

• Stay indoors with windows closed during thunderstorms.• Be aware of poor air quality days that result from stagnant air. These

days are most likely to occur during hot summer months.• If certain weather conditions seem to trigger asthma, patients should ask

their health care providers about preventive use of asthma medications.

Although not clearly understood, some relationship seems to existbetween thunderstorms and an increase in asthma symptoms.

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that come with thunderstorms,” saysSilkoff. “During the allergen seasons,thunderstorms blow in largeamounts of allergens from the coun-tryside. This means people who areallergic to grass or tree pollens areexposed to vast amounts. That resultsin epidemics of asthma.”

Another factor for this associationmay be the ozone, a well-establishedasthma trigger, created during thun-derstorms. “Some people havehypothesized that the ozone createdwhen lightening strikes increasesozone levels in the air, and that, inturn, triggers asthma exacerbation,”says Moss. “However, this is just ahypothesis at this time.”

Barometric PressureChanges in barometric pressure alsoare suspected as a potential asthmatrigger. “There are patients who saytheir asthma worsens with changes inthe weather,” says Moss. “Usuallythey are referring to a change in thebarometric pressure, and that’s diffi-cult to prove. There are a lot of anec-dotal reports of people having diffi-culty at those times, but there are alack of studies with strong support-ing data.”

The key to barometric pressuremay be the accompanying tempera-ture fluctuations. “There are studiesthat have suggested that increasedbarometric pressure affects asthma,”says Silkoff. “In fact, some indicateboth increased barometric pressureand large temperature fluctuationsduring the day are connected to anincrease in asthma.”

What role, if any, the mechanismof barometric pressure plays is notwell understood at this time, but it isan interesting area for further scien-tific investigation.

PollutionIn evaluating the relationshipbetween weather and asthma, onehas to consider the effect of weatheron pollution. “There’s a weather sys-tem called an ‘inversion’ where the

air actually sitsstill,” says Silkoff.“What that doesis concentrate allthe airborne pol-lutants, which canworsen asthma.”This condition isseen most dramat-ically in largecities where heatand sunlight reactwith pollutants tocreate largeamounts ofground-levelozone, a substanceknown to be a potent asthma trigger.

Avoidance andPreventionIf certain weather conditions causean increase in asthma symptoms, oneof the first things a person can do issimply be aware of the pattern. Agood way to develop this awarenessis to keep a diary to track asthmaflares and weather conditions simul-taneously. To track asthma flares,individuals should record dailysymptoms and readings from a peakflow meter (a small hand-held devicethat allows a person to measure lungfunction by blowing into it). Once apattern of weather triggering asthmais clear, a person can take steps to tryto avoid these weather conditions.

“We can’t change the weather, butwe can avoid exposure to it to someextent,” says Silkoff. “If patientsexercise outside and know that cer-tain weather conditions make asthmaworse, they should exercise indoorson those days. If they are aware offeeling worse on a particular day,they should plan activities in a fash-ion to accommodate this.”

While avoidance is perhaps thebest solution, avoiding the outdoorenvironment entirely is impossible.Using asthma medications appropri-ately, based on patterns of asthmaexacerbations, can be very effective.“If a person has reproducible symp-

toms with certain events or certainchanges in the weather,” explainsMoss, “using a bronchodilator, suchas albuterol at the onset of thosechanges, may help prevent symptomsfrom occurring. But a note of cau-tion: if a quick-relief medication isneeded frequently, the person shouldsee an allergist and be evaluated forthe need for controller medications.”

Although we cannot change theweather, we can educate ourselvesand our health care providers aboutthe symptoms that seem to occur asa result of it. Understanding personalasthma triggers and patterns helps usavoid or prevent asthma episodes.

Gretchen W. Cook is a freelance writerin Jackson, Mississippi, who specializesin family and health topics. She wasdiagnosed with asthma at age 6.

Reprint orders: Mosby, Inc., 11830 WestlineIndustrial Dr., St. Louis, MO 63146-3318;phone (314) 453-4350; reprint no.78/1/117644doi:10.1067/mas.2001.117644

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