Tobacco companies started to add ammonium salts, such as diammonium phosphate [(NH4)2HPO4], to cigarettes. When lit, the salts convert to ammonia (NH3). The ammonia takes protons from acid form nicotine molecules, turning them into the easier-to-absorb, conjugate base form.
The conjugate base form of nicotine feels harsh and scratchy to the back of the throat. The acid form of nicotine is reported to feel milder and smoother when inhaled, but the lungs don’t absorb it as readily.
Researchers who have studied vaping liquids have suggested that this difference in smoothness between acid and conjugate base nicotine might contribute to the popularity of Juul, which first appeared in stores in 2015. Its discreet, thumb-drive-like design, and fruity flavors helped Juul quickly become a top seller. By early August 2019, Juul products accounted for 72% of total e-cigarette sales.
A 2018 study led by David Peyton at Portland State University to evaluate various brands of e-cigarettes found that the two Juul liquids they tested contained mostly acid form (smoother feeling) nicotine.
Peyton and his colleagues also found that Juul pods contained approximately 57 milligrams (mg) of nicotine per milliliter (mL) of solution. Other brands, including Twelve Vapor, Nicquid, and Beard Vape Co., averaged 10 mg of nicotine per mL of solution. Most of the non-Juul brands’ liquids had more than 50% of the harsher, conjugate base form of nicotine.
Peyton and his co-authors see a parallel between the different nicotine forms they found in e-cigarettes and the tobacco companies’ discovery in the 1960s. In an email interview, Peyton noted that “the combination of high-nicotine concentrations and low conjugate base form, like Juul has, will make for a flavor and perception by users that is not harsh, as if the e-cigarette liquid had very little nicotine.”
In the study, however, the quantity of nicotine in the two Juul flavors was higher than in other e-cigarette liquids tested. How much actually gets absorbed by the lungs is another question.
Your brain on nicotine
Research has found that nicotine is bad news, particularly for teenagers, whose brains are still developing.
Among other effects, such as increasing a person’s risk of high blood pressure and diabetes, nicotine boosts the level of dopamine in the brain. Dopamine is a neurotransmitter, a type of chemical released by neurons to send signals to other nerve cells. Dopamine is involved in the activation of the brain’s pleasure and reward centers. Normally, the levels of this neurotransmitter go up when you earn a good grade on a test, win a race, or reach the next level in a computer game. The dopamine makes you feel good about your accomplishment.
When a drug like nicotine artificially causes a dopamine surge, it induces that same positive feeling. The problem is that when the effect wears off, smokers or e-cigarette users want to repeat the experience, so they take more of the drug. This pattern of use and reinforcement can lead to addiction.
This is especially dangerous for teens. Adolescence is a critical period for brain development. Research suggests that nicotine exposure could re-wire teens’ brains with harmful, long-term consequences. For example, it can lower users’ cognitive skills, increase the likelihood that they will try illicit drugs, and increase their risk of developing mental health disorders.
Aside from nicotine, flavorings in vaping liquids could have their own set of health effects. Preliminary lab studies involving human endothelial cells, which line the lungs, have shown that some of the flavored liquids used in e-cigarettes cause significant damage to the cells.
How all of these health factors will play out in the next few years to decades is still unknown. But what recent illnesses and studies on e-cigarettes thus far have shown is that a lot more research is needed to understand the health risks of vaping.