Allergic reactions can range from mildly uncomfortable to life-threatening, as in a severe asthma attack. These people have very sensitive airways that can react to various irritants, making breathing difficult. The number of people who have asthma has greatly increased in recent years up 61 percent between 1982 and 1994, to a total of 14.6 million persons in the United States. Asthma in children under 18 years of age increased by 72 percent in the same period, to a total of approximately 5 million children. The number of deaths from asthma rose 45.3 percent between 1985 and 1995, to more than 5,600 deaths annually.
Most infectious diseases pass from person to person through physical contact.
Crowded conditions with poor air circulation can promote this spread. Some bacteria and viruses thrive in buildings and circulate through indoor ventilation systems. For example, the bacterium causing Legionnaires' disease, a serious and sometimes lethal infection, and Pontiac Fever, an influenza-like illness, have circulated in some large buildings. Some fungi are known to produce toxic substances as a by-product of their metabolism, which can cause a variety of adverse health effects. Short-term symptoms can include dermatitis, respiratory irritation, headaches and fatigue.