For the second time in less than a week research indicates  e-cigarettes may not be as harmless as many may think, though researchers note the devices still meet Food and Drug Administration approval.

The latest study says vapor particles from deep inhalation may be getting lodged into lung tissue. But what damage or impact that may bring is still an unknown. The potential risk is that the particles could play health havoc for those who have any sort of respiratory issue such as asthma.

The research team, at RTI International, say the particles are about the size found in cigarette smoke and 40 percent are reaching the deepest part of a smoker's lung.

"These small particles have a high surface area-to-volume ratio," a researcher said. "When they deposit in your lungs, it makes it easy for whatever chemicals are in them to dissolve into your lung tissue."

The research team also stated that cancer-causing agents produced by traditional tobacco products are not in e-cigarettes.

"Everything we found was what the [U.S. Food and Drug Administration] and others generally regard as safe," a researcher said, noting the cancer-causing agents produced by burning tobacco are not present in e-cigarettes.

The latest news is part of a stream of reports and data coming to light about e-cigarettes. One recent study noted they're becoming too attractive to youngsters and some want federal government regulations on marketing.

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