London (CNN) The fluid in e-cigarettes could cause a potentially life-threatening lung condition in some people, British doctors have warned, after a 16-year-old boy suffered respiratory failure in a rare case that has been linked to vaping.

The teenager had a fever, a persistent cough and increasing difficulty breathing for around a week, and was initially suspected to have asthma.

But after his condition worsened in hospital and the boy experienced respiratory failure, doctors found he was suffering from hypersensitivity pneumonitis -- a condition in which the air sacs and airways in the lungs become severely inflamed.

The cause was "likely to have been an exaggerated immune response to one of the chemicals found in e-cigarette fluid," the doctors now report.

"There are two important lessons here. The first is always to consider a reaction to e-cigarettes in someone presenting with an atypical respiratory illness. The second is that we consider e-cigarettes as 'much safer than tobacco' at our peril," the doctors wrote in a report of the case published in the journal Archives of Disease in Childhood.

Read More