The cause of asthma is unknown. Studies suggest a strong link between asthma and atopy, the hereditary presence of antibodies associated with allergic reactions. Exposure to environmental allergens can trigger asthma symptoms. Among the most common allergens are microscopic droppings of dust mites and cockroaches, airborne pollens and molds, plants and plant proteins, enzymes, and pet dander (minute scales of hair, feathers, or skin).
Exposure to a variety of occupational irritants (e.g., vapors, dust, gases, fumes, tobacco smoke, air pollution) also can worsen or cause asthma.
Certain medications may trigger asthma symptoms. These include beta-blockers, used to treat high blood pressure (hypertension), heart disease, and glaucoma (in eye drops). About 5 to 20 percent of adults with asthma have attacks triggered by sensitivities or allergies to medications such as aspirin, ibuprofen, indomethacin, and naproxen. Others react to sulfites (chemicals commonly used to preserve foods such as tuna, salads, dried apples and raisins, and beverages such as lemon juice, grape juice, and wine).
Other factors that may contribute to asthma or worsen symptoms include sinus infections, gastroesophageal reflux disease (GERD), pregnancy, menstruation, and even the time of day. Asthma also can be induced by exercise or cold air.