Q. Do room humidifiers do more harm than good? My doctor recommends them for times when my children have colds and coughs, but I recently read that they can also spread germs and disease. How does one use them properly, or should we get rid of ours altogether? Do they really help during a bout with the flu?

A. Humidifiers add moisture to dry air, soothing dry, irritated mucus membranes, the sensitive tissue lining our nose and throat. They are used mostly in the winter months when the humidity in the air is low. Humidity is especially low in homes with forced-air heat.

Dry air in itself can cause throat irritation and aggravate dry, itchy skin. Many people find that humidifiers help their symptoms of colds, flu and asthma.

However, I don't know of any evidence that humidifiers actually clear up head or chest infections faster -- they just make some people feel better.

One problem with humidifiers is that they can serve as a breeding ground for mold or mildew. Many people are allergic to household molds, in which case using a humidifier might backfire and make runny noses and chest congestion worse. In rare cases, certain molds may cause a lung reaction that resembles asthma or pneumonia.

The solution to this problem is to clean the humidifier regularly with a disinfectant cleaner and be careful not to let the room get too humid. If you have a humidistat, you can adjust the room's relative humidity to between 40 and 45 percent. Higher humidity encourages mold to grow.

Cool-mist vaporizers can make a room feel cold and damp, but steam vaporizers -- which emit superhot jets of water vapor into a room -- can be dangerous, if children are likely to play nearby.

If you do use a vaporizer, I recommend the cool-mist type. Change the water daily and clean the unit regularly to avoid mold. If you see any mold growing on the vaporizer, you can disinfect it by running a very dilute solution of chlorine bleach and water through it (a few teaspoons of bleach in a quart of water). Vent this to the outside -- the fumes can be irritating -- and then rinse out the unit with plain water.

If you have forced-air heating, you can attach a humidifier directly to your heating unit. Otherwise, you can use the free-standing variety available at department or appliance stores.

The most efficient is the ultrasonic type, which sprays a fine mist that stays suspended in the air for long periods and doesn't make the room feel damp, as some other types do. Ultrasonic humidifiers also run silently.

If you don't want to buy a humidifier, an inexpensive way to add water vapor to the air is to place pans of water on radiators (not electrical heating units). The heat makes the water evaporate into the air.

Q. I had intestinal surgery several years ago and now feel a mass in my abdomen. My doctor says it's caused by hardening of the scar from the previous surgery and that I should live with it. My concern is that this condition will require surgery in the future, and because of this I have been reluctant to make travel plans.

A. Most incisions in the skin heal with a narrow band of firm scar tissue underlying the visible scar. Occasionally, the body reacts to this scar tissue by depositing calcium in it, making it nearly rock hard.

For an incision in the abdomen, a calcified scar can be quite large and extend in a hard band for a couple of inches on either side of the scar and several inches deep. A calcified scar usually takes months or years to fully develop and can contain so much calcium that it shows up on an X-ray almost as dense as bone. In general, there's no reason to do anything about a calcified scar, other than making sure it's not some other type of tumor. Otherwise, I see no reason you couldn't travel.

Rarely, injury to a muscle can trigger the body to make calcium deposits in it, much like those that can occur in abdominal muscles cut during intestinal surgery. Called myositis ossificans, this condition need only be treated if it's causing pain or interfering with movement.

Jay Siwek, a family physician from Georgetown University, practices at the Fort Lincoln Family Medicine Center and Providence Hospital in Northeast Washington.

Send questions to Consultation, Health Section, The Washington Post, 1150 15th St. NW, Washington, D.C. 20071.