The sleep/socks question has at least four aspects:
hygiene (sweaty feet….hmmmm)
aesthetics (not exactly a fashion statement)
procreation (neither are they an aphrodisiac)
sleep science (the right heat = happy feet = happy sleep)
Here’s the science bit
Humans are endotherms. Unlike lizards, who need to bask in the sun to start their day, we are able to themoregulate ie we can maintain our own body temperature.
Thermoregulation is clever stuff (here’s an explainer) Essentially it ensures our vital organs are always operating at the optimal temperature. Anywhere outside the range 92.3 -104.9 F and you’ll be in serious trouble.. or dead.
One of the biggest body temperature changes throughout the 24 hour cycle happens whilst we sleep. See the graph below.
Typical body temperature throughout the day
In normal sleepers body temperature is lower at night than it is during the day. This temperature drop starts at the onset of tiredness and continues to around 4am in the morning. Research has shown that a cool room is optimal for restful sleep.
Here’s the interesting bit (for sleep geeks anyway)
According to research, the ideal ambient temperature for your sleeping environment is between 60-67 deg Fahrenheit. (15.5-19.4 deg C).
But overall body temperature consists of two ‘zones’ which both have to be satisfied to eliminate sleep disturbances:
core temperature (regulated by the brain)
shell temperature (influenced by external temperature)
The key, it seems is to hit the sweet spot. Neuroscientist Dr. Eus van Someren tested this in an experiment using thermosuits. The suits made subtle skin temperature manipulations to patients while they slept. These small adjustments Someren found, made a significant improvement in sleep quality.
While a dip in core temperature before bedtime flips on your brain and body’s “time for bed” switches and helps you fall asleep, Someren’s research shows that keeping your skin temperature “perfectly comfortable” is important when it comes to maintaining deep, restful slumber.
So what has all this got to do with feet?
It turns out that your feet are perfect for regulating external temperature. Natalie Dautovitch Professor of chronopsychology explains that your feet:
contain specialized vascular structures that help with heat loss. Specifically, the hands and feet contain blood vessels called the arteriovenous anastomoses, which — coupled with the lack of hair on the bottoms of your feet — are perfectly designed to help dissipate body heat.
Hence it turns out that sleeping with one, or both feet out of the covers is an amazingly useful life-hack to improve the quality of your sleep.
Whilst there are other ways to keep cool at night, removing your socks and dangling a foot or two out of the covers could be the most convenient solution.