One person walks through offices, factories and stores, spraying an aerosol canister of influenza and common cold viruses.

Another person, sick with the flu, sneezes or coughs into the air.We label the first person a terrorist and demand an immediate arrest and severe punishment. Yet we react with kind expressions of concern to the second.

How strange!

People who sneeze or cough into the air are real health menaces. They spread infectious diseases that can hurt other people, physically and economically.

About 70 million Americans get at least one cold each year. Up to 50 million get influenza. Most of the victims just feel terrible. Some die from pneumonia and other complications. Time lost from work alone costs the economy billions of dollars each year.

Sneezing and coughing can spread pneumonia, tuberculosis, whooping cough and other diseases.

Part of the blame rests with our cough and sneeze reflexes, which are difficult to control. Coughing and sneezing are beneficial, producing a whoosh of pressurized air that cleans the respiratory passages, removing irritants and mucus. Irritants in the nose, throat or lung usually trigger the reflex, which involves nerves, respiratory muscles, the vocal cords and other structures.

Just before a sneeze or cough, the respiratory muscles undergo a powerful contraction that builds up high-pressure air in the lungs.

In a cough, the vocal cords clamp shut and then suddenly open, allowing a blast of air to escape through the mouth. In a sneeze, muscles in the soft palate at the back of the mouth contract to direct air through both the nose and mouth.

Each blast expels from the body a fine aerosol mist of saliva droplets and minute particles of mucus. Yes, it's the splatter visible when you sneeze or cough onto a mirror.

The mist billows out from mouth and nose at speeds of more than 70 mph and then hangs suspended in the air.

Droplets containing influenza viruses or other microbes may remain for two hours after a sneeze, according to researchers at the National Institutes of Health.

People probably tolerate sneezers and coughers because the droplets cannot be seen or felt. But they are there - waiting for you. You inhale them. They cling to the moist membranes of your eyes, lips, mouth and tongue.

Unpleasant? Yes. Researchers suspect that relatively few encounters with the droplets result in disease. You may have immunity to the viruses in Joe's or Jane's sneeze, for instance, or the viruses may no longer be infectious.

But if conditions are right, genetic material from the virus invades your cells. It orders your cells to stop their normal work and begin producing new virus particles. You are about to get sick.

Antihistamines, cough-suppressants and other medications can, of course, reduce the frequency of coughs and sneezes. People try to block others with a facial tissue, a hand, a forearm.

In some people, the reflex is so sudden there is no time for protective action. Others don't recognize the importance of covering the mouth and nose. Sadly enough, others don't care.

We need to be more aware of the role of coughing and sneezing in spreading infectious diseases. We should end the ridiculous custom of blessing people who sneeze in public.

We need more research on the role of coughing and sneezing in spreading influenza and colds in schools and workplaces. It may establish whether supervisors should send a sick person home with pay, for instance, rather than risk having sneezes and coughs infect other employees.

As individuals we need to remember a basic health rule. Yes, Mother was right: Cover your face when you sneeze or cough, and teach your children to do so. And carry facial tissues or a handkerchief when you're sick.

Distributed by Scripps Howard News Service