This study from Germany reported by WebMD appears to be common sense, since environmental factors, such as temperature and sound, affect sleep. Nonetheless, still interesting to think about:

A bedroom that smells good may make for sweet dreams, while a stinky sleep setting may lead to bad dreams.

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.