Eighteen people have now died in the suites of a lung disease linked to e-cigarettes, the US Public Health Agency reports. More than 1,000 people have fallen ill, a quarter of which have been added in the past week. Nearly 40 percent of the sick are under 20 years old.

The authorities do not yet know exactly what caused the deaths, but products containing tetrahydrocannabinol (THC), an active substance in cannabis, are suspected. When interviewing just over 500 of the sick, 77 percent stated that they used THC products. 16 percent said they only used nicotine products.

"Similar to chemical burns"

According to a study by the Mayo Clinic, which was published this week in The New England Journal of Medicine, some of the lung ulcers are similar to chemical burns, the New York Times reports. The researchers likened the damage to those you get from breathing in mustard gas.

The study was conducted on 17 people, two of whom have died. About 70 percent of them had used marijuana or cannabis oil.

Brandon T. Larsen, one of the doctors behind the study, says that the diseased lungs look like "a worker in an industrial accident where a large thin of chemicals was spilled and that person was exposed to it and suffered a chemical burn to the lungs."

He goes on to say that the injuries cause swelling on the lungs and fluid can leak in, which makes it impossible to breathe. According to him, it is not possible to say whether the sick survivors will be fully restored.

Prohibition also in India

Those affected in the US who smoked e-cigarettes are in 48 states. The deaths have occurred in 15 of them. Several states have now banned flavored e-cigarettes or discouraged use.

In September, India also decided to ban the import, sale and production of e-cigarettes, citing health risks.