Many teens wrongly think light or occasional smoking isn’t bad for them, according to an analysis of a nationwide youth survey.

“Our findings suggest that decades of anti-tobacco work have succeeded in convincing adolescents that heavier smoking patterns are dangerous,” said lead author Stephen M. Amrock of the New York University School of Medicine.

But they are wrong to think that lighter smoking is not very dangerous, he said.

“Even the occasional cigarette truly is bad for you. Light and intermittent smokers face tremendous future health risks,” Amrock told Reuters Health by email.

Decades of research have found that even light and intermittent smoking increases the risk of cancer and heart disease, the leading killers in this country, he said.

Amrock and his coauthor Dr. Michael Weitzman used survey answers from almost 25,000 teens in grades six through 12 from the 2012 National Youth Tobacco Survey.

Asked about smoking, kids could respond that a particular pattern caused no harm, little harm, some harm, or a lot of harm.

Almost 90 percent of the teens knew that heavy smoking, defined as smoking at least 10 cigarettes per day, is very harmful, the authors report in Pediatrics.

But only 64 percent knew that light smoking - having a few cigarettes per day - is very harmful, and only 33 percent knew that intermittent smoking on some days but not every day is very harmful to health.

The kids also answered questions about their own recent use of cigarettes or alternative tobacco products. Nine out of ten kids did not smoke at all.

Boys and Hispanic or black teens were most likely to believe that light and intermittent smoking is less harmful, as were those who were already light or intermittent smokers themselves.

Only 35 percent of light smokers and 14 percent of intermittent smokers thought their own level of tobacco use was causing a lot of harm.

Many teens and adults do smoke intermittently, and can stick to this pattern without transitioning to heavy smoking for many years, Amrock said.

Number and frequency of cigarette smoking are not the only ways to estimate danger to health, according to Paulo D. Vitoria of the Portuguese Council for Smoking Prevention in Lisbon.

“One issue at the circumstances level is the use frequency and how a person uses or smokes,” Vitoria, who was not part of the new study, told Reuters Health by email. “For instance, adolescents that smoke with less frequency can smoke in a more dangerous way, inhaling deeper or longer.”

The risk of intermittent smoking is not lower than that of regular smoking – only different, Vitoria said.

Some “light” smokers don’t even think of themselves as “smokers,” Amrock said, “despite the fact that their tobacco use puts them at tremendous health risks down the line.”

It may also be easiest for these smokers to quit, he noted.

Addressing the misconception that light or intermittent smoking is safer or low risk is an important strategy for preventing kids from starting to smoke,

“Preventing tobacco use is among the most cost-effective things we can do as a healthcare system,” Amrock said. “Making sure that all teens understand just how dangerous all tobacco is an important first step in curbing tobacco use nationwide.”