The chemical formula for water is H₂O, whether it's in liquid or vapor form. But the chemical formulas for the ingredients in e-juice are a lot more complex. In liquid form, this study identifies at least 64 different chemical compounds in e-juice, and at least 82 different chemical compounds once it becomes a vapor—including cancer-causing toxins like formaldehyde. These new compounds are produced as byproducts of the chemical reactions that happen when e-juice gets heated. Click here to see the scientific studies on these toxic chemicals and which ones are harmful to your health.

The nicotine in vapes is either “freebase” or nicotine salt. Freebase nicotine gets slowly absorbed in the bloodstream. Nicotine salts, however, deliver nicotine directly to the air sacs in our lungs for a stronger “hit” that more closely replicate the way cigarettes deliver nicotine in the lungs. Check out this study for more scientific research on the nicotine salts in vapes.

Human DNA naturally replicates to replace damaged or dead cells. But formaldehyde can mess this up. This scientific study explains how formaldehyde can cause DNA lesions, and if our body can’t fix that damage, that changed version of the DNA continues to get replicated.

Lead, nickel, chromium, cadmium, copper, and tin are just some examples of metals that have been found in e-cig vapor across these different studies. Scientists have shown that the metal from e-cig/vape heating coils seep into the e-juice or vape juice and end up in the vapor. The heating coils are usually made out of Kanthal® alloy, which is made up of aluminum, chromium, and iron; or Ni-200, used in the heating coils in JUUL® and Puff Bars, which is made up of nickel and chromium.

This scientific study shows the pulegone in mint or menthol e-cigs and vapes is nowhere near what the FDA considers to be safe. The way they assess cancer risk of synthetic food additives like pulegone is through “margin of exposure” (MOE). An MOE of 10,000 or below is considered to be unsafe. Pulegone in electronic nicotine delivery devices had an MOE of 325–3,084, well into the danger zone.

Aldehydes are chemicals used to flavor e-juice. When flavor aldehydes like cinnamaldehyde, vanillin, and benzaldehyde mix with propylene glycol, the basic liquid in e-juice, they produce a new chemical compound called “aldehyde PG acetals.” This study shows that 50%–80% of the toxic acetals in e-liquid are in the vapor that gets inhaled.

Diacetyl is a butter flavoring that’s found in different food products like microwave popcorn. While it’s safe to eat, it’s not safe to inhale as a vapor. In the early 2000s, factory workers who processed microwave popcorn experienced serious lung disease called bronchiolitis obliterans or “popcorn lungs,” and some even required lung transplants. This study found diacetyl in 39 of 51 e-liquids tested, including in tobacco and menthol flavors.

The National Toxicology Program, a federal program run by the U.S. Department of Health and Human Services, conducted this series of studies to test the effect of pulegone on mice and rats. They found that pulegone caused early deaths among the mice and rats due to liver toxicity. They also found that pulegone is associated with nephropathy, a renal (kidney) disease that prevents the kidney from filtering waste from the body.

When heated at high temperatures, propylene glycol and vegetable glycerin form toxic compounds, like acetone, acrolein, formaldehyde, and acetaldehyde. This study shows that higher e-cig voltage, which results in higher temperatures, increases the level of cancer-causing chemicals found in e-cig vapor. Specifically, increasing the battery power from 3.2V to 4.8V can cause formaldehyde, acetaldehyde, and acetone levels to increase 200 times. In fact, the level of formaldehyde detected was similar to levels of formaldehyde found in cigarette smoke.

This report summarizes all the different scientific research studies that have identified over 100 different chemicals across 50 brands of vape liquids and have shown that some of the chemicals in vape juice and vapor are known to cause cancer, respiratory diseases, and heart disease.

As of January 2020, there were over 2,600 vape-related hospitalizations. 15% of hospitalized patients were under 18 years of age. Hospitalized patients included people who vaped nicotine only, vaped THC only, or vaped both. Think that vapes are safe as long as they are not bought on the streets? Think again—69% of hospitalized patients who vaped nicotine said they only buy their vapes from stores. The CDC keeps track of these numbers on this webpage.

Check out the 10 Facts about What FDA Does and Does Not Approve to help quit tobacco use. Fact: E-cigarettes are not an approved method. In fact, e-cigs contain some of the same toxic chemicals found in regular cigarettes.

Most of the scientific studies on e-cigs have been done to better understand the health effects of vapes, but officials are starting to be concerned about the environmental impact of e-cigs production and disposal processes. Even the CEO of Philip Morris International, a major player in the tobacco industry, acknowledged “new challenges [they] need to address, in particular increased use of water and energy at the manufacturing level, and the management of electronic waste.” This study found that lead leaked from discarded e-cigs at a high enough concentration to be considered hazardous waste.

The nicotine in e-liquid is either freebase nicotine or nicotine salts. With freebase nicotine, the higher the nicotine content, the harsher the hit. With nicotine salts, the compound is less volatile, making it a smoother hit regardless of nicotine level, which you can read more about in this research study. Because the smoothness masks the level of nicotine, it makes it easier to inhale too much at one time, resulting in “nic sickness.”

Symptoms of being “nic sick” include nausea, stomachache, tremors, and dizziness. To check out more nic sickness symptoms, check out this blog from the American Lung Association.

This study tracked the nicotine exposure and mental health of over 1,000 people from birth until age 25. The scientists determined that there is a cause-effect relationship, and cigarette smoking increases the risk of depression. For more about nicotine’s effects on the developing brain (including addiction, mood, and cognitive function) see this CDC resource, which summarizes current research on the topic.

The 1988 Surgeon General Report entitled, “The Health Consequences of Smoking: Nicotine Addiction,” summarized over 2,000 scientific studies, and concluded that nicotine is as addictive as cocaine and heroin. This older report isn’t available online, but you can read more about it in this news article. While these studies are about cigarettes, the nicotine in cigarettes and the nicotine in e-cigs/vapes are both highly addictive and have the same negative effects.

The prefrontal cortex of our brain regulates our planning, short-term memory, and decision-making, including impulse control and risk-taking. This study showed how young adults who smoked cigarettes had lower prefrontal cortex activity than teens who never smoked. They also found that the longer they smoked (in years), the lower their prefrontal cortex activity was.

This report summarizes findings from 52 different scientific studies about the effect of nicotine on sleep, and found that tobacco users needed more time to fall asleep, and experienced more disturbances when they do sleep. In fact, 20% of heavy smokers woke up every night because they craved nicotine.

Nicotine does more harm to the teenage brain than adult brains because our brains develop until we are about 25 years old. Being exposed to nicotine at an early age makes our brain a lot more sensitive to addiction. The CDC summarizes research showing how nicotine exposure during adolescence can interfere with brain development and increase addiction risk. In general, our brains have receptors called nicotine cholinergic receptors (nAChRs) that nicotine binds to. A series of studies found that nAChRs activity and expression was higher in young mice than adult mice, and young mice were more likely to self-administer nicotine than adult mice. We know from decades of medical research that the effects of chemicals and drugs on mice are similar to the effects on humans.

The nicotine receptors, nAChRs, release a chemical in our brains called dopamine, also known as “the happy hormone.” Because dopamine makes us feel good, it tricks the brain into getting more and more nicotine, forming the basis for addiction. Repeated exposure to nicotine desensitizes the receptors and builds nicotine tolerance. Learn more about how nAChRs affect our brain here.

Even without nicotine, vaporized propylene glycol and vegetable glycerin are harmful to our lungs. This study looked into the lung cells of mice that were exposed to four different conditions for four months: air only, cigarette smoke, e-juice with nicotine, and e-juice without nicotine. They found that the lung cells of mice that had been exposed to e-juice without nicotine had dysfunctional lung immune systems. In fact, the mice died when exposed to a small amount of the flu virus, even when they looked healthy otherwise. Scientists use mice for these studies since it would be unethical to do these tests on humans. But we know from decades of cancer studies that human organs react very similarly. You can read news coverage of the study here and here.

This study shows that e-cig vapor causes “mucociliary dysfunction,” which happens when human airway cells can’t clear out phlegm or mucus from our bodies effectively. The phlegm and mucus also gets stickier and thicker than normal. Many lung diseases, like asthma, emphysema, and COPD are characterized by this condition.

We also know that the effects of vaping can start when you’re young thanks to this scientific study, which collected data from over 6,000 high school students, and found that teens who currently vaped were 48% more likely to have asthma compared to those who never vaped.

Platelet-activating factor receptor (PAFR) is a molecule produced by cells that line human airways. Pneumococcal bacteria, which causes pneumonia, sticks to the PAFR in our airways, so increased PAFR levels means increased risk of infection. This study found that PAFR levels increased 3 times among people who vape in the cells lining their noses, even when measured an hour after they last vaped. They also found that the bacteria doubled in airway cells that have been exposed to e-cig vapor, with or without nicotine.

This study looking at lung tissue samples of people who vaped found that the lung’s immune cells, macrophages, had a “fine, foamy-looking appearance that is characteristic of chemical injuries.” Breathing difficulty among vape users is likely because the observed lung cells had tissue damage and dead cells that block the airways, causing fluids to leak into the air sacs. Check out news coverage of the study here.