What is mainly talked about in this news item? [originaltext] The dangers of

The dangers of smoking tobacco have been well documented since the 1960s. For years, health experts have also warned about the dangers of second-hand smoke-breathing in other people’s cigarette smoke. Now, some researchers are sounding the alarm over what they call "third-hand smoke". Third-hand smoke is the tobacco contamination that remains after a cigarette is extinguished. Dr. Jonathan Winickoff of Harvard University has been studying it.