Certain irritants or allergies can trigger an asthma attack, which causes the airways of the bronchial tubes to constrict, resulting in extreme difficulty in breathing due to the inflammation and increased mucous produced by the lungs, according to MedlinePlus. Tightness of the chest, wheezing and coughing indicate swollen and irritated airways. Antihistamines prevent asthma attacks by blocking histamine, which induces an attack by effecting cell receptors. First-generation antihistamines are over-the-counter medications with mild sedative qualities. Second-generation antihistamines do not cause sedation, and generally require a prescription. Individuals afflicted with asthma should always seek professional medical treatment before using any asthma product.
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As a first-generation antihistamine, diphenhydramine usually causes mild sedation, the University of Iowa Hospitals and Clinics says. Diphenhydramine dramatically reduces sneezing, runny nose, itchiness, watery eyes and rashes, including hives and affiliated symptoms, according to Drugs.com. Diphenhydramine and related antihistamines can decrease or prevent the onset of bronchial constriction caused by histamine, exercise or allergens, the American Academy of Allergy Asthma and Immunology reports. Using this medication in conjunction with other asthma prescriptions may cause problems; monitoring by a medical professional is essential.
A 1987 National Institutes of Health study found that cetirizine effectively reduces bronchoconstriction by relaxing the smooth muscles surrounding the airways in patients with mild asthma. The improved breathing capability is comparable to that produced by the use of bronchodilator medications. According to Drugs.com, cetirizine is a second-generation antihistamine that effectively inhibits the release of histamine into the body. This medication generally requires a prescription, although reduced-strength forms are available over the counter. Asthma sufferers should always consult a physician prior to use.
Loratadine is a widely prescribed second-generation antihistamine with no sedative properties. A 2002 U.S. National Institutes of Health report found that loratadine effectively reduced exercise-induced asthmatic symptoms. This antihistamine aids in decreasing the effects of seasonal allergies that cause itching of the throat and nose, sneezing and runny noses, according to Drugs.com. Physicians recommend daily application of this antihistamine during allergy seasons or for individuals who experience asthma symptoms during and after exercise.