While overall smoking rates are falling in the United States, a new study points to one exception: Young women who often opt for "very light" smoking.
The study defined a very light habit as smoking five or fewer cigarettes a day.
For the research, a team led by Carole Holahan of the University of Texas at Austin looked at data from nearly 9,800 women ages 18 to 25 who took part in a federal government survey in 2011.
Very light and intermittent smoking -- using cigarettes on some days but not others -- was common among the women.
Nearly 20 percent of all the women in the study, and about 60 percent of current smokers, were described as very light smokers, and nearly half of the current smokers did not smoke every day. Younger women were more likely to be very light and intermittent smokers than heavy or daily smokers, Holahan's team found.
Compared to other smokers, very light smokers were much more likely to be intermittent smokers, to be from a minority group, and to have some college education. They were also less likely to be married, the study found.
One expert said young women shouldn't fool themselves into thinking light smoking is harmless.
"Even light smoking can triple the lifetime risk of heart disease," said Dr. Len Horovitz, a pulmonary specialist at Lenox Hill Hospital in New York City. "More efforts need to be directed at this cohort of emerging young women who smoke lightly," he added.
Another anti-smoking expert said very light smokers might not even consider themselves smokers at all.
"They may not even consider themselves to be smokers and that they can quit easily," said Patricia Folan, who directs the Center for Tobacco Control at North Shore-LIJ Health System in Great Neck, N.Y. "For this reason, practitioners need to be sure to ask their patients, particularly young women, 'When was the last time you used tobacco.' If patients are asked if they smoke, the very light and/or nondaily smokers may say no."
"Light and nondaily smokers often increase their smoking over time and become daily, heavier smokers," she added.
Certain people might be more vulnerable to taking up a "light" smoking habit, the Texas researchers added. They found that -- like other smokers -- very light smokers were more likely to have suffered depression at some point in their life, and to report past-month mental distress or substance use.