It's indisputable that too many teenagers are smoking cigarettes, but what's less clear is why they do so, a new study indicates.

Reuters reported Sept. 11 that researchers from the University of Montreal found that the risk factors for youth smoking are so varied -- ranging from self-esteem and parental smoking to alcohol use, age, and level of academic success -- that interventions need to be highly individualized

Researcher Jennifer O'Loughlin and colleagues studied risk factors for smoking among youths entering their teens and tracked them for five years. Nearly half of the 877 students studied tried smoking during the study period, and 21 percent became daily smokers.

They found that the leading risk factors for smoking included use of alcohol and other tobacco products, having friends or siblings who smoked, having parents or teachers who smoked, living in a single-parent family, poor academic performance, feeling stressed, acting impulsively, and feeling the need to smoke.

Researchers also identified factors that were not associated with smoking risk, including gender, physical activity, parents education, feeling depressed, worries about weight, novelty-seeking and watching TV.

The findings were published in the Sept. 1, 2009 issue of the American Journal of Epidemiology.