All e-cigarettes emit toxic chemicals, according to a new study. Levels of these chemicals are affected by a number of factors, including temperature, type and age of the device, HealthDay reports.

Levels of toxic vapors increase between the first few puffs and later puffs as the e-cigarette gets hotter, the researchers report in Environmental Science & Technology.

“Advocates of e-cigarettes say emissions are much lower than from conventional cigarettes, so you’re better off using e-cigarettes,” study co-author Hugo Destaillats of Lawrence Berkeley National Laboratory said in a news release. “I would say, that may be true for certain users — for example, long-time smokers that cannot quit — but the problem is, it doesn’t mean that they’re healthy. Regular cigarettes are super unhealthy. E-cigarettes are just unhealthy.”