Scientific American spoke with Rebecca N. Gaughan, an ear, nose and throat (ENT) doctor in private practice in Olathe, Kan., to learn the answer. An edited transcript follows.

SA: What causes laryngitis?

RG: The most common form of laryngitis is usually caused by a virus, just like a cold is caused by a virus. So you can catch it from other people.

SA: Is it different from straining your voice by using it too much?

RG: There are different causes of laryngitis. Most people think of laryngitis as a cold-like illness. But laryngitis can also be caused by straining the voice, as in yelling at a football game or forcing oneself to speak very loudly in front of a group without a microphone. Laryngitis itself is just the swelling of the vocal chords, which are part of the larynx. The key is, if you have hoarseness or an unusual voice for more than three to four weeks, then you need to get your voice box checked by a physician who can look at your vocal chords. It could be something more serious, even cancer.

SA: What would the treatment be if you were diagnosed with the viral form?

RG: The treatment for the viral form is similar to the treatment for the common cold. Drink noncaffeinated fluids, rest, perhaps use a humidifier and, most important, do not strain your voice. Don't whisper, don't raise your voice or talk for long periods of time. Resting your voice helps. Unfortunately, most people tend to keep talking and forcing their voice, causing more strain and hoarseness.

SA: So it's bad to whisper if you have laryngitis?

RG: Whispering is one of the worst things you can do because it's like yelling. It strains, or pulls, on the vocal chords. Instead you want to try to take a deep breath and then exhale as you talk. Try to relax your voice and not strain it.

SA: What is the effect of caffeine on your vocal chords when you have laryngitis?

RG: Caffeine dehydrates you. You want to drink noncaffeinated fluids to hydrate yourself so the mucus in your throat and around your voice box stays watery and protects your vocal chords. If you are not getting enough water, or you drink a lot of caffeinated fluids, you will make thicker, drier mucus that is less lubricating.

SA: How long might someone expect to show symptoms of laryngitis?

RG: Anywhere from five to 14 days. If it's lasting longer than 14 days, you have to think that there's something else, other than a virus, causing the hoarseness.

SA: What exactly happens to the vocal chords during a bout of laryngitis?

RG: The vocal chords become swollen. They are dry, irritated and swollen, and your voice doesn't sound normal. Instead you have a kind of breathy, whispery voice.

SA: Is laryngitis more common during the winter?

RG: Yes, laryngitis is more common in the peak flu and cold season, usually November, December and January.

SA: In general, how common is laryngitis?

RG: Much fewer people get laryngitis than colds. An average adult gets up to three colds a year, and a three-year-old child averages eight colds a year. In contrast, most adults get an average of one bout of laryngitis a year or one every couple of years.

SA: What about the less common types of laryngitis?

RG: Sinus drainage or a severe cough can also cause laryngitis. Coughing forces the vocal chords together and can cause swelling and irritation. Reflux, or acid entering the throat from the stomach, is another possible cause of throat clearing and laryngitis. Laryngitis from acid reflux needs to be evaluated by an ENT doctor.

The key thing is that if it's not better in three or four weeks, see someone who can actually look at your vocal chords in order to evaluate them.