The respiratory system bears the brunt of the suffering when we catch a cold (or in reality, when a cold catches us!). Cold symptoms are not produced directly by the cold virus, but by the body's nonspecific defenses as they fight the virus.

The immune system learns to recognize specific disease agents through exposure to them. This exposure can occur through vaccination or by natural means. We acquire immunity to chicken pox, measles, mumps, tetanus, cholera, smallpox, and many other life threatening diseases. So, one might wonder, if the immune system can do such amazing things, why can't it defend us from the common cold?

We are susceptible to at least 200 different cold-causing viruses. The most common types, rhinoviruses (literally "nose viruses"), cause about 40% of all colds in adults. As soon as the immune system learns to recognize and defend us from one, another comes along, and then another. This viral diversity creates quite a challenge for the immune system, so much so that most people succumb to one to six colds per year.

Research evidence indicates that cold viruses may be transmitted from the hands of an infected person to the hands of a susceptible person. The virus can survive on the skin for only a few hours and must reach the nose in order to invade the body. On the face near the nose is no good, because the skin provides an effective barrier. Since the mucous membranes of the mouth are also an inhospitable environment, kissing seldom spreads colds.

If all goes well for the virus, eventually the hand delivers the virus to its new home, the person's respiratory system, by touching the mucous membranes of the nose or the eyes (the virus can travel down the tear duct to the upper nose). One study found that 40 to 90% of people with colds had rhinoviruses on their hands. The viruses were also found on about 15% of nearby objects, such as doorknobs, telephones, and coffee cups. Some evidence also suggests that cold viruses can fly through the air with the greatest of ease and find new homes in new noses. They may spread when expelled by coughing and sneezing.

It is not known what makes some people more susceptible to colds. Small children are the most susceptible, because their immune systems are still immature and haven't learned to recognize as many pathogens. People who are around children a lot also get colds more often. Smokers are more likely to catch colds than nonsmokers, partly because smoking inhibits the airway cilia that help move mucus. Some studies have shown that stress can decrease the effectiveness of the immune system, and some evidence suggests that stress and fatigue increase susceptibility to colds.

Given what we know about the transmission of colds, the single best way to prevent colds is frequent handwashing, especially when you're around people who have colds. Avoid sharing telephones, glasses, towels, and other objects with a person who has a cold. And try not to touch your nose or eyes. People with colds should cough and sneeze into facial tissues and then throw the tissues away.

Getting enough rest, eating well, exercising moderately, and managing stress certainly won't hurt and may help keep your resistance up. If you're a smoker, cold prevention is yet another good reason to quit.

What about vitamin C? Although studies have failed to show that vitamin C prevents colds, some research has found that it may lessen the severity of cold symptoms. Vitamin C also increases the integrity of cell membranes and so may make them harder for viruses to penetrate.

Since a cure for colds continues to elude medical researchers, the best we can do is to treat the symptoms. It's been said that with aggressive medical treatment a cold will disappear in seven days, while if left alone a cold will last a week. Nevertheless, treatment of symptoms can at least make us feel better until the cold has run its course.

The first step in cold self-care is to decide whether your symptoms are those of a cold or something more serious requiring medical attention. People who have heart disease, emphysema, diabetes, or other health conditions should get professional advice before initiating self-care, especially before taking over-the-counter medication. Pregnant and lactating women should also check with their doctors before taking any medication.

1. Chicken soup, broth, or other hot drinks. Your mother was right: Hot fluids help relieve congestion by increasing the flow of nasal secretions. They also soothe irritated throats.

2. Gargle with salt water (l/4 teaspoon salt in 8 oz water) to soothe a sore throat.

3. Use a vaporizer or humidifier to increase humidity, especially if the air is very dry. Humid air is gentler on nose and throat.

4. Breathing steam gives your nose a temporary fever, creating an inhospitable environment for the virus. It also helps to thin the mucus causing a stuffy nose, and thus temporarily relieves congestion. The steam may also feel soothing to irritated throats and nasal passages.

5. While rest may not hasten your recovery, it may help you feel better. It's good to stay out of circulation for the first few days of a cold to keep others from getting it and to be sure that what you have is a cold and not something more serious.

6. Many over-the-counter cold medications are available. If you decide you need something, avoid combination drugs that contain several active ingredients to treat several symptoms. If, instead, you buy single drugs for the symptoms you wish to treat, you will avoid taking unnecessary drugs and decrease unpleasant side effects.