Participating in Dangerous Activities
The Gemara (Brochos 32b and Shavuos 36b) derives from the pesukim "But beware and watch yourself very well" (Devarim 4:9) and "And you shall watch yourselves very well" (Devarim 4:15) that it is prohibited to deliberately enter into a dangerous situation or participate in a hazardous activity. Similarly, the Gemara (Shabbos 32a) states, "a person should never stand in a place of danger saying that Hashem will perform a miracle for him, lest in the end Hashem will not perform a miracle for him." This prohibition is later codified by the Rambam (Hichos Rotzeach 11:4-5) and the Shulchan Aruch (Choshen Mishpat 427). The Beis Yosef (Yoreh Deah 116) cited by the Beer Hagolah (Choshen Mishpat ad. loc.) claims that it is likely that this prohibition is in fact of Biblical origin and severity even though it does not carry the penalty of lashes (see Minchas Asher, Devarim Sec. 7.) Moreover, since a life of Torah and mitzvos can be physically demanding at times, the Rambam (Hilchos Deios 4:1) emphatically prescribes that all unhealthy activities be avoided whenever possible.
Hashem Protects the Simple
At the same time, the Gemara in numerous places (Shabbos 129b, Yevamos 12b, 72a, Avodah Zarah 30b, and Niddah 31b) permits the performance of regular activities that entail a certain measure of risk based upon the reasoning, "but nowadays, when the multitudes have trodden upon this matter, the pasuk 'Hashem protects the simple' (Tehillim 116:6) is applied." Rav Chaim Ozer Grodzinksy (Achiezer 1:23) argues that this rule only permits situations involving minimal amounts of risk which are therefore negligible in the minds of most participants. Alternatively, Rav Elchonon Wasserman (Koveitz Shiurim, Kesubos 136) notes that the Gemara only applies this principle to routine activities that are essential parts of daily life. Indeed, perhaps the permitted level of risk that can be tolerated should vary somewhat depending upon the necessity and measure of potential benefit to be derived from the activity [see Noda Beyehudah, vol. 2, Yoreh Deah 10]. However, recreational activities that entail more substantial, and therefore noticeable and perceptible, levels of risk would undoubtably be prohibited.
Smoking
When smoking tobacco was first introduced to European Jewry it was regarded by some as a digestive aid and a generally innocuous if not healthy habit (see Pnei Yehoshua to Shabbos 39b and Mor U'ketziah 511.) However, as the harmful effects of smoking were beginning to emerge, the Chafetz Chaim (Likkutei Amarim 13) strongly condemned smoking where it was thought to be deleterious to health. Nonetheless, until relatively recently it was still assumed by many poskim that only a small minority of smokers actually became ill as a result, and therefore smoking, while not advisable and discouraged, was still permitted under the banner of "Hashem protects the simple", particularly for those who had already become addicted (see Iggros Moshe, Yoreh Deah volume 2 siman 49, Choshen Mishpat volume 2 siman 76, as well as Kovetz Teshuvos 1:19.) In more recent times, as the pervasive perils of smoking have come to be understood and appreciated, it has been resoundingly prohibited by virtually all recognized poskim including those who had initially taken a more permissive stance (see Le'torah Ve'horaah 5772 pg. 67, Viyshma Moshe pg. 436, and Teshuvos Vehanhagos 1:159 and 316, 3:354, 4:115.)
Vaping and Juuling
Over the past few years the use of e-cigarettes has become a rapidly emerging trend. The e-cigarette is a handheld electronic device that simulates the experience of smoking by heating a liquid, containing propylene glycol, glycerin, flavoring, and nicotine, called e-juice or e-liquid, to generate an aerosol, called a vapor, that the user inhales. Initially e-cigarettes were targeted and used primarily by those who were trying to quit smoking, and therefore it was understandably celebrated and received favorably in some circles. However, precisely because of its acceptability, availability, sophisticated appeal, and variety of flavors (numbering in the thousands), the practice of "vaping" quickly migrated to the adolescent population, including a large percentage of whom were never smokers or likely smokers. The most popular form of vaping, now called "Juuling" involves an e-cigarette called a Juul, which appears like a flash drive that can be conveniently charged on any computer and easily camouflaged. It utilizes e-juice cartridges called "pods" that are available in many popular flavors and contain a unique formula that can deliver nicotine in higher concentrations.
In August of 2016 the FDA banned the sale of e-cigarettes to minors. However, the popularity of e-cigarettes and Juuling amongst teenagers and young adults has continued to skyrocket at an alarming rate, and the design of the e-cigarette and the contents and concentrations of the e-liquid are not regulated, contributing further concern and volatility to the situation. In January of 2018 The National Academies of Sciences, Engineering, and Medicine published a comprehensive study which concluded that while the use of e-cigarettes appears less harmful than conventional cigarettes, e-cigarettes emit numerous known toxins aside from nicotine. Studies have shown that e-cigarette emissions can include potentially toxic levels of formaldehyde, arsenic, benzene, chromium, manganese, nickel, lead, zinc, and diacetyl, etc. Even though some of the ingredients in e-juice have been designated as safe when consumed at room temperature, when they are heated by a metal coil they produce toxic substances that are potentially dangerous. These findings have been discussed in many recent news columns including Medical News Today, Newsweek, and The New York Times.
Other recent studies published by the Proceedings of the National Academy of Sciences, Society for Research on Nicotine and TobaccoUC San Francisco, American Journal of Respiratory and Critical Care MedicineJournal of Allergy and Clinical Immunology, American Physiological Society, and Pediatrics have suggested that prolonged inhalation of these toxins can possibly lead to an increased risk of cancer, heart disease, stroke, and respiratory distress. In addition, the NASEM as well as Pediatrics have conclusively shown that the use of e-cigarettes among adolescents has been linked to the eventual use of conventional cigarettes. Even though the precise long-term effects of regular e-cigarette use remains largely undefined, since it involves the frequent inhalation of known toxins, Rav Hershel Schachter shlit"a and Rav Mordechai Willig shlit"a believe that there is already ample basis to assert that the use of e-cigarettes by non-smokers should provisionally be forbidden by virtue of the prohibition against self-endangerment found in the pasuk "And you shall watch yourselves very well," pending the collection of definitive data.
E-Juice, Glycerin, and Kashrus
E-cigarettes present additional halachic considerations including the issue of kashrus supervision. Often one of the core ingredients in the e-liquid is glycerin, a clear, odorless liquid with a thick consistency and sweet taste. It is also a common ingredient in many food and pharmaceutical products where it contributes moisture, thickness and sweetness. Glycerin can be derived from vegetable oils or animal fats and they are used interchangeably. Therefore, a food product containing glycerin typically requires kashrus supervision despite the insistence of the manufacturer that it uses strictly vegetable glycerin. Arguably, a glycerin product that is turned into an aerosol or vapor and then inhaled should also require kashrus certification. Indeed, this is the opinion of the Chicago Rabbinical Council and reported to be the position of Rav Shlomo Miller shlit"a as well.
The Shulchan Aruch (Yoreh Deah 108:5) quotes the opinion of Rava (cited by the Gemara Avodah Zarah 66b) who permits the oral inhalation of forbidden wine vapor. However, Tosfos declares that this is because the vapor of the wine is caustic and offensive, but in essence Rava concedes that orally inhaling the concentrated vapor of forbidden food which is pleasant and commonly inhaled is akin to drinking it and would be prohibited (see also Shiltei Hagiborim Avodah Zarah 32a, Emunas Shmuel cited by Pischei Teshuvah 108:5, and Minchas Yaakov 36:38.) Moreover, the Ramo prohibits simply tasting forbidden foods even when they are not swallowed. Technically the vapor produced by e-cigarettes is an aerosol, which is the suspension of solid particles or liquid droplets in gas. Therefore, when inhaling the vapor produced by e-cigarettes, small amounts of the e-juice can be tasted and even swallowed, as evidenced by the marginal caloric intake involved in vaping.
It is conceivable that since e-juice in its raw liquid state has a foul taste, it has permanently forfeited its status as a forbidden food, based upon the Gemara (Avodah Zarah 67b) which posits that forbidden foods that have an unpleasant flavor are no longer considered "food" and thus are permitted. However, Rav Shlomo Zalman Aurbach (Minchas Shlomo 1:17, 2:64) demonstrates from the Gemara (Bechoros 7a), which is hesitant to unequivocally declare donkey urine as sufficiently foul tasting so as to be permitted, that the threshold of disgust to allow forbidden foods is quite high. It is doubtful whether or not the raw flavor of e-juice, which is not intended to be drunk but occasionally leaks into the vapor, is adequately dreadful to surrender its status as a forbidden food.
Additionally, the Magen Avraham (467:10) prohibits cigarettes containing beer-soaked tobacco on Pesach, even though the tobacco is presently inedible (see Beis Meir.) Rav Moshe Schick (Maharam Schick, Orach Chaim 242) explains that since the beer-soaked tobacco is designed for inhalation and it has a pleasant flavor when inhaled, the tobacco can still be considered fit for consumption and remains prohibited. This is presumably predicated upon the notion that inhalation can sometimes be considered a form of imbibing (see also Magen Avraham 210:9). Similarly, since the e-juice is intended for inhalation and enjoyable when inhaled, it would retain its status as a forbidden food and as a result it should require kashrus supervision.
Conclusion
Vaping is an addictive recreational activity which entails the inhalation of known toxins and possibly forbidden foods, and therefore should be avoided entirely. The Ramo (Yoreh Deah 116:5) citing the Gemara (Chullin 10a) states in this context, "be careful of all things that cause danger, because danger is treated more severely than transgressions, and one should be more careful with an uncertain danger than with an uncertain issur." While the medical community is a long way from completing its study of e-cigarettes, that is a process that could take years if not decades and, unfortunately, we simply don't have the luxury of waiting. Vaping has already made considerable and disturbing inroads amongst the youngest and most vulnerable members of our community, which requires us to act decisively and preemptively by implementing appropriate precautions. May Hashem guide us in dealing with this new challenge and continue to protect us in all of our endeavors as the pasuk states, "Hashem will guard your going out and your coming in from now and to eternity" (Tehillim 121:8).