Toxic chemicals aren't the only harmful thing a person breathes in when they vape. Most vaping devices also contain the drug nicotine. This is the same highly addictive chemical found in other tobacco products like traditional tobacco cigarettes and smokeless tobacco ("dip"). In fact, one Juul pod contains as much nicotine as a whole pack of cigarettes.
Using nicotine causes changes in the brain that make a person crave more of the drug. When someone vapes, nicotine gets into their bloodstream through their lungs and travels to their brain within 10 seconds. The drug causes a surge of a brain chemical called dopamine, which is known as a reward chemical. That means it makes the person feel good, encouraging them to vape some more. This can lead to addiction.
Teens are more vulnerable to addiction than adults because the brain continues to develop through a person's mid-twenties. Exposing an adolescent's brain to nicotine can cause effects on attention, learning, and memory that promote addiction to nicotine. Studies also show that teens who vape are more likely to start smoking traditional cigarettes. One likely explanation is that they've become addicted to nicotine.