Nicotine salt

Nicotine salts are salts consisting of nicotine and an acid.[1]  They are found naturally in tobacco leaves.

Research
Research on nicotine salts is limited.[3]  Possible health risks of persistent inhalation of high levels of nicotine salts are not known.[3] "Juul products use nicotine salts, which can lead to much more available nicotine," Principal Deputy Director Dr. Anne Schuchat of the Centers for Disease Control and Prevention (CDC) stated in September 2019.[4]  She also stated that the nicotine salts "cross the blood brain barrier and lead to potentially more effect on the developing brain in adolescents."[4]

Types
A nicotine base and a weak acid such as benzoic acid or levulinic acid is used to form a nicotine salt.[1]  Benzoic acid is the most used acid to create a nicotine salt.[5]  Nicotine pyruvate is another form of nicotine salt.[6]  A chemical reaction with a pyruvate acid is used to aerosolize nicotine.[7]

Level and rate of delivery
A free-base nicotine solution with an acid reduces the pH, which makes it possible to provide higher levels of nicotine without irritating the throat.[8]  Nicotine salts are thought to amplify the level and rate of nicotine delivery to the user.[3]  The speed of nicotine salts uptake into the body with the use of electronic cigarettes is close to the speed of nicotine uptake from traditional cigarettes.[9]  Traditional cigarettes provide high levels of nicotine, but with the bad taste of smoking.[10]  Pod mods, however, can provide high levels of nicotine without the negative smoking experience.[10]  Nicotine salts are less harsh and less bitter, and as a consequence e-liquids that contain nicotine salts are more tolerable even with high nicotine concentrations.[5]  Nicotine salts in aerosol form do not generate the sensation of irritation in the chest and lungs that regular cigarettes do.[9]  Protonated nicotine salt is easier for less experienced users to inhale.<sup id="cite_ref-JenssenBoykan2019_11-0">[11]

Brands
The latest generation of e-cigarettes, "pod products," such as Juul, have the highest nicotine content (59 mg/mL), in protonated salt, rather than the free-base nicotine form found in earlier generations.<sup id="cite_ref-JenssenBoykan2019_11-1">[11]  In June 2015, Juul introduced a pod mod device containing nicotine salt.<sup id="cite_ref-McKelveyBaiocchi2018_12-0">[12]  British American Tobacco stated that they have been using nicotine salts in their US Vuse e-liquid brand since 2012.<sup id="cite_ref-Becker2018_13-0">[13]

There has been a proliferation of pod-based products with high nicotine concentration, triggered by Juul's financial success.<sup id="cite_ref-JacklerRamamurthi2019_5-2">[5]  As of September 2018, there were no less than 39 similar Juul devices as well as 15 Juul-compatible pods being offered.<sup id="cite_ref-JacklerRamamurthi2019_5-3">[5]  Tested show that the pod mods Juul, Bo, Phix, and Sourin contain nicotine salts in a solution with propylene glycol and glycerin.<sup id="cite_ref-GoniewiczBoykan2018_3-3">[3]

Marketing
Advertisements state nicotine salt liquids contain 2 to 10 times more nicotine than those found in the majority of regular e-cigarette products.