More than 80 percent of popular brand e-cigarettes sold in the U.S. that were examined in a new study were contaminated with bacterial and fungal toxins.

Researchers from Harvard’s T.H. Chan School of Public Health found glucan in 81 percent of the products– single use cartridges and refillable e-liquids. Endotoxin was found in 27 percent of them. Exposure to the two microbial toxins have been shown to cause asthma, inflammation and reduced lung function in occupational and environmental settings.

David Christiani, Elkan Blout Professor of Environmental Genetics and senior author of the study said: "Finding these toxins in e-cigarette products adds to the growing concerns about the potential for adverse respiratory effects in users."

E-cigarettes may also contain diacetyl, a chemical linked to serious lung disease, according to the U.S. Surgeon General, who also warns about:

• ultrafine particles that can be inhaled deep into the lungs
• volatile organic compounds and
• heavy metals, such as nickel, tin, and lead

The use of e-cigarettes has skyrocketed in recent years, particularly in young people. The devices heat a liquid into an aerosol that the user inhales. The liquid usually has nicotine and flavoring in it, and other additives. The nicotine in e-cigarettes and regular cigarettes is addictive. E-cigarettes are considered tobacco products because most of them contain nicotine, which comes from tobacco.

The study has been published online in Environmental Health Perspectives.