The study, which examined 75 popular e-cigarette products—cartridges (single use) and e-liquids (refillable material)—found that 27% contained traces of endotoxin, a microbial agent found on Gram-negative bacteria, and that 81% contained traces of glucan, which is found in the cell walls of most fungi. Exposure to these microbial toxins has been associated with myriad health problems in humans, including asthma, reduced lung function, and inflammation.