Question: Do people fart in their sleep?
Short answer: Yes.
Long answer: In a previous post, we observed that the smelliness of farts varies with the time of day. Peaks in smelliness can be observed at regular intervals, suggesting a possible link to meal times or other circadian rhythms. However, our previous analysis did not consider farts that occur during sleep.
Previous work has suggested that people continue to fart while sleeping. In some cases, this kind of farting can be associated with medical conditions, but most often it is just part of the regular cycle of gas release that defines human existence. Despite a few accidental measurements of sleep farts, the phenomenon has not to our knowledge been investigated systematically.
We recently performed a series of experiments in which we placed one of our air quality sensors under the blanket of a sleeping member of the College. This was done with the consent of the subject and the full approval of our ethics committee. The sensor tracked the levels of VOCs throughout the night, providing a picture of the timing of farts during sleep. Here are the data from an example session:
The spikes in VOC levels correspond to sleep farts that began 2 – 3 hours after the onset of sleep and continued for another 2 hours or so. After that, there was little farting activity until waking.
Here are the data from a second experiment, showing a similar pattern:
From a physiological standpoint, the onset of sleep farting corresponds roughly to the phase of sleep in which there are “micro-awakenings”. These are periods during the sleep cycle when the subject awakens briefly, interrupting REM sleep. Periods associated with deeper sleep occur early in the sleep cycle, and in our data, they are associated with fewer farts.
Thus, it seems that farts are most likely to occur when subjects are not deeply asleep. This makes sense, as the external anal sphincter must be relaxed voluntarily, under conscious control, to allow the release of fart gas. This voluntary control is necessary to prevent incontinence and it permits the possibility of controlled fart release when subjects are awake. But another consequence of this physiological mechanism is that fart gas might build up during the night, leading to larger-than-average morning farts.