Why does everyone in Beijing seem to have a cold all winter? What is the difference between a cold and the flu? How can I increase my resistance?

Bugs, known more scientifically as bacteria and viruses, are just like people. They are slightly different everywhere you go. Your body develops immunity to bugs that you are frequently exposed to. Conversely, when you go somewhere new, you are vulnerable to new bugs that your body has never been exposed to before. This is one reason new arrivals in Beijing often receive a nasty cold as a welcome present. Beijing's notoriously foul air does not actually cause you to get a cold but it may exaggerate the symptoms of a cold and slow down your recovery.

So why do you get colds even when you are used to the local bugs? A British center dedicated to investigating colds found that all the things your mother told you are not true: colds are not caused by wearing wet clothes, sitting in a drafty room, not wearing hat and gloves etc. We know that although infection caused by breathing in viruses is common, hand to mouth infection is just as likely. Washing your hands frequently during an epidemic could help protect you.

The common cold is brought to you by any one of two hundred viruses. The symptoms include runny nose, sore throat, red eyes, sneezing and headache. These symptoms may be accompanied by weakness and general body aches. As the cold progresses the nasal mucus may become thicker and you start to realize why there is so much spitting in Beijing. A cold usually lasts about a week, but may linger for much longer and this seems to be more true in Beijing than in other places.

There is no cure for the common cold. We have developed antibiotics that will kill almost all bacteria but viruses which are much smaller than bacteria are not as easy to handle. We have developed vaccines against some viruses such as polio, rubella (german measles) and varicella (chicken pox), but a vaccine against the cold remains elusive. It is quite common in China to have a massive injection of antibiotics for even minor complaints but antibiotics do not kill the cold virus and are not recommended.

Influenza or the flu is another viral disease. It occurs in epidemic form. The symptoms are usually more severe, come on more quickly and are more general in nature than those of a cold. Fever, chills, muscle aches, fatigue and weakness are common symptoms. You know the feeling even your toenails hurt. Symptoms last about five to seven days and recovery can be as sudden as the onset. The flu virus is a clever little devil. It manages to change its appearance every year and comes back in a new form just to make producing a truly effective vaccine more difficult. It is thought that the flu virus does this little mutating act right here in our backyard: the major world flu epidemics all originate in Northern China.

Flu shots that are available here do not give complete protection but are helpful in preventing and moderating the disease.

Treatment for both colds and influenza is symptomatic. We can't kill the viruses, so treatment is aimed at making you feel better while your body heals itself. The best treatment is lots of rest and drinking fluids in great quantities. Acetomin-ophen (Tylenol or Panadol) is useful in keeping a fever under control and relieves aches and pains. Aspirin is no longer favored and should NEVER be given to children or teenagers. Ibuprofen is a safe Aspirin-like product and can help to keep fever and inflammation under control. It must be taken with food and it is better not to use this medication on children.

There are at least four other medications worth mentioning. They are often packaged in combinations. Guaifenesin is a good expectorant a medicine that helps you get rid of the phlegm associated with a cough. Dextrometh-orphan, often called DM, is a cough suppressant that I think is useful to take at bedtime These two medicines come together in medications such as Robitussin DM and Tussin DM. Antihistamines such as Chlortrimeton and Benadryl are useful in drying up a runny nose and have the added benefit of aiding sleep if taken at bedtime. Nasal sprays give an immediate feeling of relief, but the effect wears off very quickly and overdosing is a real worry. Read the instructions carefully to make sure. Afrin, one of the the most widely used nasal sprays, should only be used twice a day.

Finally, Pseudoephedrine (Sudafed) is a decongestant good for relieving that stuffed-up feeling but should be avoided in patients over 60 years old and by people with a cardiac condition.

Unfortunately viral illnesses don't always just go away. Sometimes a secondary bacterial infection develops. This leads to the confusion about the use of antibiotics for colds and flu: antibiotics are used to combat secondary infections. If you develop any of the following symptoms you should see a doctor:

- Wheezing or difficulty breathing;

- Coughing up yellow or green sputum;

- Pain in the sinuses below the eyes;

- Sore throat with neck tenderness;

- Ear pain that is more than stuffiness;

- Any fever over 39.5 degrees C (103 F) or a fever over 38 degrees C (100.4 F) lasting for two days.

What do I do when I get a cold myself? Well after decrying folk knowledge in a previous paragraph, I have to admit I usually use the treatment favored by my mother. Two Tylenol and a glass of hot milk with a huge dose of whisky at bedtime. You sleep, you sweat, you dream, and you really do feel better in the morning. H Dr. Moreton is an Obstetrician and Gynecologist at Beijing United Family Hospital.

Email your questions to Doctor Doctor at beijingscene@bigfoot.com