That news comes from a German study in which a positive smell (roses), a negative smell (rotten eggs), or a neutral smell wafted through a sleep lab while 15 healthy young women slept.
When the women entered REM sleep, the researchers woke them up and asked them what was on their minds just before waking.
The women described the dreams they'd been having and rated how positive or negative those dreams had been.
The women reported more positive dreams when they had smelled the rose scent during sleep, and more negative dreams when they had smelled the scent of rotten eggs during sleep.
The type of scent didn't affect how long the dreams lasted or how bizarre the dreams were.
It would be interesting to see if pleasant scents smelled during sleep affect nightmares, say the researchers, who included Michael Schredl, PhD, of the sleep laboratory at the Central Institute of Mental Health in Mannheim, Germany.
Their findings were presented yesterday in Chicago at the annual meeting of the American Academy of Otolaryngology - Head and Neck Surgery.