Asthma is a chronic condition in which the airways of the lungs become narrow due to muscle spasm, inflammation, and excess mucus.
This produces symptoms like trouble breathing, wheezing, and coughing. For some people, these symptoms show up only in response to specific triggers — like pollen or other allergens, exercise, or even weather changes. In others, asthma symptoms flare during sleep or even daily.
There are different categories of asthma, most of which are defined by their triggers or symptoms. For example, nocturnal asthma is a type that comes on at night while you’re in bed; occupational asthma is caused by exposure to specific chemicals or pollutants at work.
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Experts say it’s often impossible to know exactly why a person develops asthma. “The disease pathways are complicated,” says Patricia Takach, MD, an associate professor of clinical medicine in the section of allergy and immunology at the University of Pennsylvania’s Perelman School of Medicine. For example, Dr. Takach says, allergy-induced asthma seems to stem from a mix of genetic and environmental factors.
Another theory, the much-debated “hygiene hypothesis,” links exposure in early life to germs and viruses with lower rates of asthma and other health problems. (1)
There’s evidence that air pollution promotes the development of asthma. (2) And there’s research linking some consumer chemicals to d asthma rates. (3) But none of these theories has been proved, and experts usually can’t explain why one person develops asthma and another does not.
That said, there are well-established asthma risk factors and triggers. There are also some evidence-backed methods for lowering your asthma risk.
