Carryover of neotame, WS-23, and other additives from popular disposable e-cigarettes to aerosol

Every time a person uses a disposable e-cigarette, they are inhaling a mist created by heating a liquid. This liquid is a complex mixture, usually containing a base fluid, nicotine, and a variety of additives designed to make the experience more appealing. Among these additives are sweeteners, which mask the bitter taste of nicotine, and synthetic coolants, which create a refreshing sensation in the throat similar to menthol but without the distinct smell. While scientists have long known that these ingredients exist inside the liquid reservoir of the device, a critical question remained unanswered: how much of these chemicals actually makes it from the liquid into the mist that the user breathes? Understanding this transfer is essential because the health risks of a substance depend heavily on how much of it enters the lungs, not just how much sits in the bottle.

A team of researchers at Yale University set out to solve this puzzle by examining the most popular disposable e-cigarettes currently sold in the United States. They focused on two specific additives that have become ubiquitous in these products: neotame, an artificial sweetener thousands of times sweeter than sugar, and WS-23, a synthetic coolant widely used to provide a cooling effect without the flavor of mint. The researchers purchased twelve popular brands and flavors of these devices, along with three Senza devices marketed as nicotine-free and two SpreeBar devices containing a nicotine analogue, to ensure their findings applied across the entire market. They did not simply guess at the contents; they physically tested the devices using a machine that mimicked human breathing patterns. The machine took twenty puffs from each device, capturing the resulting mist in a frozen trap that condensed the vapor back into a liquid for analysis. By comparing the amount of each chemical found in the original liquid to the amount captured in the mist, the team could calculate exactly what percentage of the additive was being inhaled.

The results revealed a clear divide in how different chemicals behave during the heating process. The synthetic coolants and nicotine proved to be highly efficient at moving from the liquid into the air. On average, eighty-four percent of the WS-23 and eighty-eight percent of the nicotine present in the liquid successfully transferred into the aerosol. Menthol and another coolant called WS-3 followed a similar pattern, with transfer rates hovering around eighty-one to eighty-eight percent. This means that when a user takes a puff, the vast majority of these cooling and stimulating agents they are exposed to are the same ones that were originally mixed into the liquid.

In contrast, the artificial sweeteners behaved very differently. Neotame, despite being present in every single device tested, had a much lower transfer rate. On average, only forty percent of the neotame in the liquid made it into the mist, with individual devices showing rates as low as fifteen percent and as high as sixty-four percent. Sucralose, another sweetener found in a few of the devices, showed an even wider and generally lower range of transfer, with only two devices containing it and rates varying between twenty-six and fifty-four percent. The researchers found that the presence of nicotine did not change these transfer rates, nor did the specific flavor of the device. The difference appeared to be rooted in the physical properties of the molecules themselves. The cooling agents and nicotine are more volatile, meaning they evaporate more easily when heated, whereas the sweeteners are heavier and less likely to turn into vapor under the temperatures generated by the device.

This study also uncovered a new detail about the composition of these products. While neotame was found in all the devices, the researchers discovered that two specific brands also contained sucralose alongside neotame. This marks the first time such a combination of two artificial sweeteners has been reported in e-cigarette products. The presence of multiple sweeteners suggests manufacturers may be layering different compounds to create a specific sensory profile, potentially to enhance the sweetness while masking any remaining bitterness. However, this practice adds another layer of complexity to the safety profile of these devices, as the interaction between these chemicals during heating is not fully understood.

The researchers were careful to note that while they measured how much of these chemicals reached the mist, they could not determine what happens to the neotame once it is heated. It is possible that some of the sweetener breaks down into other substances during the process, which would explain why less of it appeared in the final mist. The study did not find evidence of new, unexplained chemicals in the mist using their standard detection methods, but the possibility of thermal breakdown remains a significant unknown. The health implications of breathing in neotame and WS-23 over a long period are currently unclear, as most existing safety data for these substances comes from studies on eating or drinking them, not inhaling them.

Ultimately, this work provides a foundational map of what users are actually breathing. It confirms that while the cooling agents and nicotine in disposable e-cigarettes are transferred to the user with high efficiency, the sweeteners are transferred less completely, though still in substantial amounts. The study establishes that users of these popular devices are consistently exposed to neotame and WS-23, regardless of the flavor or the nicotine content. These findings do not declare the products safe or unsafe, but they provide the necessary data for future toxicological studies to determine the long-term health effects of chronic inhalation of these specific additives and their potential breakdown products.