Sweet smells, such as those of roses, cause people to experience pleasant emotions in their dreams, according to a new study from the University Hospital in Manheim, Germany.

The odour of rotten eggs had the opposite effect on the 15 sleeping participants, they told the American Academy of Otolaryngology.

In the study, the researchers waited until participants had entered REM sleep and exposed them to a high dose of smelly air for ten seconds and woke them up a minute later.

The subjects were then asked about the content of their dreams. It was found that they rarely dreamed of smelling something, but the emotional tone of the dream changed depending on the stimulation, the BBC notes.

In news that could have implications for the treatment of sleep disorders, Professor Boris Stuck and his colleagues believe it is possible that exposure to smells could help improve the sleep of people who suffer from nightmares.

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