<P> A 2014 review found higher levels of carcinogens and toxicants than in an FDA - approved nicotine inhaler, suggesting that FDA - approved devices may deliver nicotine more safely . In 2014, The World Lung Foundation stated that "Researchers find that many e-cigarettes contain toxins, contaminants and carcinogens that conflict with the industry's portrayal of its products as purer, healthier alternatives . They also find considerable variations in the amount of nicotine delivered by different brands . None of this information is made available to consumers so they really don't know what they are ingesting, or how much ." </P> <P> A 2014 review found "Various chemical substances and ultrafine particles known to be toxic, carcinogenic and / or to cause respiratory and heart distress have been identified in e-cigarette aerosols, cartridges, refill liquids and environmental emissions ." Few of the methods used to analyze the chemistry of e-cigarettes in the studies the review evaluated were validated . </P> <P> The primary base ingredients of the liquid solution is propylene glycol and glycerin . About 20% to 27% of propylene glycol and glycerin - based liquid particles are inhaled . The long - term effects of inhaled propylene glycol has not been studied, and is unknown . The effects of inhaled glycerin are unknown . Being exposed to propylene glycol may cause irritation to the eyes and respiratory tract . The risk from the inhalation of propylene glycol and glycerin is probably low . Propylene glycol and glycerin have not been shown to be safe . Some research states that propylene glycol emissions may cause respiratory irritation and raise the likelihood to develop asthma . Long - term inhalation of propylene glycol indoors could increase risk to children to develop asthma . To lessen the risks, most e-cigarettes companies began to use water and glycerin as replacement for propylene glycol . The inhaled glycerin could cause lipoid pneumonia . </P> <P> Some e-cigarette products had acrolein identified in the aerosol . It may be generated when glycerin is heated to higher temperatures . Acrolein may induce irritation to the upper respiratory tract . Acrolein levels were reduced by 60% in dual users and 80% for those that completely switched to e-cigarettes when compared to traditional cigarettes . E-cigarettes vapor have been found to create oxidants and reactive oxygen species (OX / ROS). OX / ROS could react with other substances in the vapor because they are highly reactive . Although e-cigarettes have been found to contain OX / ROS at about 100 times less than in cigarette smoke, they probably induce meaningful biological effects . </P>

What are the health effects of e cigarettes