MOST CIGARETTE SMOKERS BEGIN HABIT BEFORE THEY'RE 18 : CHECKUP.

The most alarming statistic about cigarette smoking isn't that millions continue to smoke in spite of the warnings, but that 90 percent of the people who take up smoking for the first time are younger than 18.

According to the American Cancer Society, it's this fact and others that made young smokers (many between the ages of 9 and 15) the focus of this year's Great American Smokeout, scheduled for Thursday.

Citing studies that 71 percent of adults who have smoked started lighting up daily by age 18, that virtually no one starts smoking during adulthood and that, while 46 million Americans have quit smoking, 3,000 adolescents try their first cigarette every day, the Cancer Society is launching a nationwide ad campaign directed specifically at teen smokers, called ``Don't Be a Sucker.''

In addition, the ACS is working with schools on the Great American SmokeScream, a seven-second scream against the tobacco industry, in an effort to convince teens that smoking is addictive and hazardous.

The Cancer Society has been battling the tobacco company for ads they claim are directed at teen-agers, including the popular Joe Camel ads, saying they encourage teens to take up smoking.

The Cancer Society estimates more than 400,000 Americans die each year from smoking-related diseases - more than AIDS, alcohol, auto accidents, fires, illegal drugs, murders and suicides combined.

One fine spray: Some shower nozzles designed to conserve water can pose a health threat, environmental researchers have found. The problem arises when water droplets are so small they can be inhaled and transport hazardous compounds into a person's lungs, said Pratim Biswas of the University of Cincinnati. Biswas and colleagues from the Environmental Protection Agency reported their findings at the annual meeting of the American Association for Aerosol Research in Orlando.

Among the three shower nozzles tested, one water-conserving model produced an abundance of inhalable particles while a conventional shower nozzle and another water-conserving model produced almost none.

Hold the Jell-O: People whose unhealthy eating lands them in the hospital may be served the same kind of food that made them sick in the first place.

An analysis of the nutritional value of hospital menus found that only four of 57 hospitals studied met the nutritional guidelines put forth by the U.S. Public Health Service and other agencies. The institutions seemed to have a particularly tough time meeting the recommendations for cholesterol (only 19 percent of the diets had low enough levels), sodium (54 percent had too much) and fiber (51 percent didn't provide enough). Half the diets were too high in saturated fat.

These institutions of healing aren't exactly serving milkshakes and bacon cheeseburgers, however. About 80 percent to 90 percent of the menus had enough servings of fruits, vegetables and grains. The analysis was based on meals served to patients without dietary restrictions.

Emergency experiments: At the end of World War II, American judges heard testimony about Nazi doctors performing horrendous medical experiments on whomever they pleased. To ensure this would never happen again, the Nuremberg code was written. The first principle of this international code was that no one could be subject to a medical experiment without giving consent. Now, for the first time in the United States, there is an exception to that code.

The Food and Drug Administration has decided that it is permissible, and entirely ethical, to enroll patients in medical studies without their consent if it is an emergency, if the patients are unconscious or cannot speak for themselves and if no relative can be reached to give consent for the patient. The new federal regulations go into effect this month.

The germs are free: It's enough to make you order by mail. Regarding germs on merchandise, Envirosell, a New York-based research firm, found tcohat lipsticks are handled by an average of six shoppers and two store employees before they're bought. Towels are touched by an average of 6.6 people. An average CD is handled 11 times before it's bought. And that's by prospective purchasers, which means the one or two salespeople who also touched your CD added their little organisms to the mix.

Pregnancy predictor: A team of researchers have developed a computer program that is twice as good at predicting a pregnant woman's due date as the traditional method, which dates back to 1838.

The computer model uses 16 factors - such as maternal age, prepregnancy weight, race, college education, alcohol and coffee use, and high blood pressure - to determine a woman's due date. The program also can determine a woman's risk of a preterm delivery, thereby alerting doctors to the need for better prenatal care.

The program is called the Mittendorf-Williams Rule and is named for its co-creators, Dr. Robert Mittendorf of the University of Chicago and Michelle A. Williams of the University of Washington.

Death by dust: The federal government has announced a new campaign to wipe out silicosis. The dreaded lung disease ``is a needless tragedy. It is preventable,'' Labor Secretary Robert Reich says. ``More than 1 million workers across the country are exposed to silica dust on the job, and 100,000 of them are at a high risk of developing silicosis.'' The disease kills about 250 Americans a year. Risky jobs include some kinds of mining, sandblasting, etching or frosting glass, stone cutting and some construction jobs.