If you smoke cigarettes, you may wonder whether switching to using electronic cigarettes, also known as vaping, exposes you to fewer potentially cancer-causing toxins. The largest study to date finds that it may—but only for people who quit smoking traditional cigarettes entirely.

Researchers at Roswell Park Comprehensive Cancer Center, working with other academic centers, evaluated data from a little over 5,000 U.S. men and women. Most were 35 to 54 years old. The researchers compared exposure to 50 different biomarkers, measurable biological substances in urine associated with disease risk, including cancer risk. They evaluated cigarette smokers, e-cigarette users, combination cigarette/e-cigarette users and nonsmokers. The study was published in JAMA Network Open.

Those who smoked e-cigarettes exclusively showed significantly lower levels of biomarkers associated with disease risk compared with cigarette smokers. But in a surprising finding, those who vaped but also continued smoking cigarettes had higher levels of risk-related biomarkers than those who only smoked cigarettes.

Many people use e-cigarettes to quit smoking, although they are not approved by the Food and Drug Administration as a smoking-cessation aid. This research suggests that while vaping may be less harmful than smoking cigarettes, it may be particularly unhealthy to vape and continue to smoke.

Click here to read the study in JAMA Network Open.

Click here to learn more about smoking and DNA damage.

To learn more about e-cigarettes and ways to quit smoking, see smokefree.gov.