"To narrow the airways" means that the tubes through which air passes in your body become smaller, making it harder for you to breathe. Full definition
The surrounding muscles tighten and mucus is produced, which further narrow the airways. (verywellhealth.com)
This often results in narrowed airways and breathing problems. (cuteness.com)
More than 25 million people in the United States have asthma, a chronic lung disease that inflames and narrows the airways causing recurring periods of wheezing, chest tightness, shortness of breath and coughing. (sciencedaily.com)