Exercise can only be harmful in bronchitis if the effort causes a great deal of coughing or difficulty in breathing. These complications can usually be avoided by taking bronchodilators prior to exercising; some people find inhaled cromolyn or nedocromil to be of special value in preventing exercise -induced bronchospasm. Deferring running outdoors if it is very cold or if the air is polluted is advisable, although wearing a simple mask such as a silk scarf over the mouth can reduce the irritation caused by cold air or pollutant particulates.