Odors Aren't Likely to Awaken Us From Sleep

June 10, 2004 -- Anyone who expects the stench of leaking natural gas or propane to wake them up from a deep sleep may be, quite literally, flirting with death.

New research from Brown University in Providence, R.I., dispels the myth that additives in gases like propane smell bad enough to wake someone up. The findings come as thousands of vacationers hit the road in their recreational vehicles, nearly all which use propane for heating water, or warming the interior of the vehicle, or cooking.

Propane, like natural gas, is odorless, so various chemicals are added to make it smell really awful. It's an unmistakable odor, so if the user is awake, the warning of a leak is instantaneous, even for a very small leak. That has probably saved thousands of lives.

But, "the idea that a smell will wake you up is not true," says psychologist Rachel S. Herz, who has spent nearly 15 years researching smells. She teamed up with Mary A. Carskadon, professor of psychiatry at Brown and a sleep expert, for the research. Their findings were published in a recent issue of the journal Sleep.

Which Comes First

Some might argue with the findings, because they remember awakening to the smell of bacon or another aroma, but the researchers say something else woke them up.

"We wake up and smell the coffee, not the other way around," Carskadon says.

Herz points out that in the early morning "you are more likely to be waking up, and you go through brief stages of actually being awake." During those short "awakenings" you may smell the bacon cooking, for example, but you smell it because you are awake, even if only for a few micro-seconds, not the other way around, she says.

Participants in the study could not be aroused from deep sleep by two distinctively different odors, but they all woke up with an auditory alarm. That has led the researchers to call for audible devices to warn of hazardous leaks.

"There has to be another stimulator, like auditory, which seems to be quite powerful, if you are at all concerned," Herz says.