Smells may influence the emotion of the dream
Sleep with flowers in your bedroom if you want sweet dreams, work suggests.
When the smell of roses had been wafted under the noses of slumbering volunteers they reported experiencing pleasant emotions in their dreams.
An odour of rotten eggs had the opposite effect on the 15 sleeping women, the German scientists found.
They told a Chicago meeting of the American Academy of Otolaryngology that they now plan to study people who suffer from nightmares.
It is possible that exposure to smells might help make their dreams more pleasant, believe Professor Boris Stuck and his team from the University Hospital Mannheim.
They waited until their subjects had entered the REM phase of sleep, the stage at which most dreams occur, and then exposed them to a high dose of smelly air for 10 seconds before waking them up one minute later.
The volunteers were then quizzed about the content of their dreams and asked how it made them feel.
The sleeping women hardly ever dreamed of smelling something. Nevertheless, the emotional tone of the dream did change depending on the stimulation.
Previous research has shown that other types of stimulation, such as sound, pressure or vibration, can influence the content and the emotional tone of dreams.
Dr Irshaad Ebrahim of The London Sleep Centre said: "The relationship between external stimuli and dreaming is something we are all at some level aware of.
"This initial research is a step in the direction towards clarifying these questions and may well lead to therapeutic benefits."
Professor Tim Jacob, an expert in smell and taste at Cardiff University, said: "Smell is the only sense that doesn't 'sleep'. Information continues to reach the limbic system of the brain and that includes the hippocampus, or memory area and the amygdala, that is involved with emotional response.
"Other senses have to pass through the 'gate' of the thalamus, which is closed when we sleep."