Introduction: What are electronic cigarettes?
Electronic cigarette is a term used to describe electronic nicotine delivery systems (ENDS), which are noncombustible tobacco products. These products use a liquid solution that contains nicotine including ingredients such as flavorings, propylene glycol, and vegetable glycerin. However, the chemical composition of e-cigarettes vary. They are different from regular cigarettes in that many e-cigarettes are reusable and the user inhales vapor rather than cigarette smoke. 
Human Health Impacts
Since electronic cigarettes have not been around for too long, their health impacts are largely unknown. More research is needed to understand the way e-cigarettes affect the human body.  According to the National Academies of Sciences, Engineering, and Medicine (NASEM), e-cigarette aerosol contains lower levels of toxic substances in comparison to smoke from traditional tobacco cigarettes.  Nevertheless, e-cigarettes can have negative health effects on users. A comprehensive 2018 report by NASEM details the findings of these effects. 
Evidence for the relation between cancers and e-cigarette use is sparse.  However, some studies have found that chemicals present in electronic cigarette aerosols (e.g, formaldehyde, acrolein) may lead to DNA damage and genetic mutations.
Studies have shown that both heart rate and diastolic (a measurement of the force your heart exerts on the walls of your arteries in between beats ) blood pressure increase a short period after nicotine intake from electronic cigarettes. There is limited evidence regarding short-term increases of systolic blood pressure (a measurement of the force your heart exerts on the walls of your arteries every time it beats ), changes in biomarkers of oxidative stress, and arterial stiffness. This is also the case with endothelial dysfunction which is where the inner lining of small arteries fails to resume its regular functions. Finally, since e-cigarettes are new to the market, there is inadequate evidence on their long-term cardiovascular impacts.
The report claims that while there is insufficient evidence on whether or not e-cigarettes cause respiratory disease, there is some evidence on minor lung function improvements in those that switch from regular cigarettes to e-cigarettes.  However — after the publication — in 2019 there was an outbreak of a vaping related severe lung illness in the United States. As of February 18, 2020, a total of 2807 deaths or hospitalized cases have been reported to the Center for Disease Control and Prevention (CDC).  Scientists suspect that these illnesses are related to Vitamin E acetate and tetrahydrocannabinol (THC) containing e-cigarettes.
As with health impacts, little is known about the environmental impacts of electronic cigarettes. However, e-cigarettes have the potential to create major disposal problems. The batteries of these cigarettes contain heavy metals including lead, chromium, manganese and nickel.  In addition, cartridges often contain residual liquid (consisting of nicotine, flavors and colorants). These components may leach into bodies of water and soil. Thus, e-cigarettes cannot be labelled as environmentally friendly.
 “Vaporizers, E-Cigarettes, And Other ENDS”. 2020. U.S. Food And Drug Administration. https://www.fda.gov/tobacco-products/products-ingredients-components/vaporizers-e-cigarettes-and-other-electronic-nicotine-delivery-systems-ends.
 “E-Cigarettes Are Harmful To Health”. 2020. Who.Int. https://www.who.int/news-room/detail/05-02-2020-e-cigarettes-are-harmful-to-health.
 “Public Health Consequences Of E-Cigarettes”. 2018. Nap.Edu. https://www.nap.edu/resource/24952/012318ecigaretteHighlights.pdf.
 “Cancers”. 2018. The National Academies Press. https://www.nap.edu/read/24952/chapter/15.
 “Blood Pressure Chart: What Your Reading Means”. 2019. Mayo Clinic. https://www.mayoclinic.org/diseases-conditions/high-blood-pressure/in-depth/blood-pressure/art-20050982.
 “Cardiovascular Disease”. 2018. The National Academies Press. https://www.nap.edu/read/24952/chapter/14.
 “Respiratory Diseases”. 2018. The National Academies Press. https://www.nap.edu/read/24952/chapter/16
 “Outbreak Of Lung Injury Associated With The Use Of E-Cigarette, Or Vaping, Products”. 2020. Centers For Disease Control And Prevention. https://www.cdc.gov/tobacco/basic_information/e-cigarettes/severe-lung-disease.html.
 Bohnenkamp, Amy. 2019. “Op-Ed: The Environment May Be At Risk From Vaping, Too”. State Of The Planet. https://blogs.ei.columbia.edu/2019/09/19/vaping-environment-risks-disposal/.
 Benham, Barbara, and Nicole Hughes. 2018. “Study: Lead And Other Toxic Metals Found In E-Cigarette ‘Vapors’”. Johns Hopkins Bloomberg School Of Public Health. https://www.jhsph.edu/news/news-releases/2018/study-lead-and-other-toxic-metals-found-in-e-cigarette-vapors.html.