***TASK*** the task is to summarize an input biomedical literature in six sentences 
    ***INPUT*** the input is a biomedical literature 
    ***OUTPUT*** the output is the summary of an input biomedical literature in six sentences 
    ***DOCUMENTATION*** 
    ***EXAMPLES*** 
    Input: Abstract Context : Electronic cigarettes ( e-cigarettes ) are becoming increasingly popular yet their effects on health remain unknown . Objective : To conduct the first comprehensive and st and ardized assessment of the acute impact of active and passive e-cigarette smoking on serum cotinine and lung function , as compared to active and passive tobacco cigarette smoking . Material s and methods : Fifteen smokers ( ≥15 cigarettes/day ; seven females ; eight males ) and 15 never-smokers ( seven females ; eight males ) completed this repeated- measures controlled study . Smokers underwent a control session , an active tobacco cigarette ( their favorite br and ) smoking session and an active e-cigarette smoking session .  Never-smokers underwent a control session , a passive tobacco cigarette smoking session and a passive e-cigarette smoking session . Serum cotinine , lung function , exhaled carbon monoxide and nitric oxide were assessed . The level of significance was set at p ≤ 0.001 to adjust for multiple comparisons . Results : e-Cigarettes and tobacco cigarettes generated similar ( p > 0.001 ) effects on serum cotinine levels after active ( 60.6 ± 34.3 versus 61.3 ± 36.6 ng/ml ) and passive ( 2.4 ± 0.9 versus 2.6 ± 0.6 ng/ml ) smoking . Neither a brief session of active e-cigarette smoking ( indicative : 3 % reduction in FEV1/FVC ) nor a 1 h passive e-cigarette smoking ( indicative : 2.3 % reduction in FEV1/FVC ) significantly affected the lung function ( p > 0.001 ) . In contrast , active ( indicative : 7.2 % reduction in FEV1/FVC ; p < 0.001 ) but not passive ( indicative : 3.4 % reduction in FEV1/FVC ; p = 0.005 ) tobacco cigarette smoking undermined lung function . Conclusion : Regarding short-term usage , the studied e-cigarettes generate smaller changes in lung function but similar nicotinergic impact to tobacco cigarettes . Future research should target the health effects of long-term e-cigarette usage , including the effects of nicotine dosage INTRODUCTION Approximately 70 % of homeless youth smoke cigarettes , but their use of alternative tobacco products ( ATPs ) is unknown . This paper reports on ATP use among past-month smokers in Los Angeles County , including whether it differs by demographic characteristics , homelessness severity , past-year quit attempts , and readiness to quit smoking . Given the growing popularity of e-cigarettes , we also report on perceptions of harm and reasons for using this product . METHODS We surveyed 292 unaccompanied homeless youth who were r and omly sample d from street sites . Participants had smoked at least 100 cigarettes during their lifetime and 1 cigarette during the past month . RESULTS Seventy-two percent of youth reported past-month ATP use ( e-cigarettes = 51 % ; little cigars/cigarillos = 46 % ; hookah = 31 % ; other smokeless tobacco product = 24 % ; chewing tobacco/moist snuff = 19 % ) . Current ATP use was unrelated to most demographic characteristics or having a past-year quit attempt . However , youth who planned to quit smoking in the next 30 days were significantly less likely to report current use of hookahs , other smokeless tobacco products , or e-cigarettes . Among lifetime e-cigarette users , the most common reasons for use included not having to go outside to smoke ( 38 % ) and being able to deal with situations or places where they can not smoke ( 36 % ) ; it was less common to report using e-cigarettes to quit smoking ( 17%-18 % ) . DISCUSSION Dual use of ATPs among homeless youth smokers is common and is more likely among those who have no immediate plans to quit smoking . Effective and easily disseminable strategies for reducing all forms of tobacco use among homeless youth are urgently needed 
    Output:
    
This literature review reported that the usage of these  e-cigarettes  was high among this population and recorded a wide variety of reasons for using e-cigarettes .
Reducing tobacco use , considering e-cigarette as less harmful , less addictive , for pleasure and peer influence , lower cost and curiosity were the most commonly reported reasons .