Highly toxic substances escape from the filters of IQOS electronic cigarettes produced by Swiss-based tobacco manufacturer Philip Morris International.
The finding, reported by the SonntagsZeitungexternal link, was made by a laboratory commissioned by the Blue Cross of Bern, Solothurn and Fribourg.
These dangerous toxins, called isocyanates, are released when polymer filters are heated to 100 degrees Celsius.
However, the laboratory did not check whether the substance is inhaled by the smoker.
"If isocyanates are inhaled during the use of IQOS, it is very problematic," warns Rainer Kaelin, a pulmonologist and former vice-president of the Swiss Lung League.
Even inhaling very small amounts, he notes, can cause serious health damage.
Isocyanates can cause illness even three months after exposure. In some extreme cases, the inhalation of isocyanates into the air has "led to fatal diseases after one year", Kaelin said.
Philip Morris acknowledges the problem, but a spokesman for the tobacco company assured the newspaper that the toxin is not inhaled when using an IQOS cigarette.
Last year Swiss producers of electronic cigarettes, and several retail outlets that sell such products agreed to a voluntary ban on the sale to minors until a Swiss law change comes into effect.