A recent German research has shown that the type of scent we inhale when we are asleep, determines the type of dreams during sleep. A positive smell can affect dreams in a positive way while negative smells make dreams negative. Earlier studies have shown affect of external stimulation, such as sound, pressure or vibration on the content and the emotional tone of dreams. The research was conducted by Professor Boris Stuck and his team from the University Hospital Mannheim.  

In this research, researchers analyzed the data collected from 15 women. When the study subjects entered rapid eye movement (REM) sleep, where dreams occur, they were exposed to three modes of smells, Aand the feel non-odorous control smell, the rose smell or the rotten egg smell. 

Researchers exposed the study subjects to a high dose of smelly air for 10 seconds before waking them up one minute later. During 40 out of 45 awakenings, study subjects reported dreams. The study subjects were told to describe the content and the ‘feel good/bad factor’ of their dreams, on an emotional “colouration” scale that measured the tone of their dream. Analysis of data showed that after the control stimulation, there was a slight positive average colouration of 0.5 and after the rotten egg smell, it was - 0.4. After smelling rose scent, average colouration was + 1.2. Researchers also found that the type of scent didn't affect how long the dreams lasted or how bizarre the dreams were. 

Dr Boris Stuck said: ‘We found that the sleeper hardly ever dreamed of smelling something. Nevertheless, the emotional tone of the dream did change depending on the stimulation.’ 

Researchers said that further study would be done to see the affect of smell on nightmares.