According to a study reported by HealthDay, teenagers and young adults who vape are almost four times as likely to start smoking traditional cigarettes as non-users of e-cigarettes.

A review of nine studies included more than 17,000 teens and young adults aged 14 to 30. Researchers found that an estimated 30% who had ever used an e-cigarette went on to use traditional cigarettes, compared to 8% of those who never vaped, according to HealthDay.

Further, respondents who said they vaped in the last 30 days were four times as likely (21.5% vs <5%) to smoke regular cigarettes, HealthDay reported.

Researchers theorized that possible nicotine addiction, peer networks, and the similarity of using e-cigarettes and cigarettes may explain the increased use of traditional tobacco cigarettes for vapers.