Ask a scientist: Feet keep us warm

Reader Question: Why do feet have such a big impact on the body's temperature? ie. if you're hot in bed sticking your foot out of the blankets puts you at the perfect temperature. Or if you are freezing you can put socks on and it warms you up immediately.

Scientist Answer: Otago University physical education professor Jim Cotter

Weird timing; when your email arrived we were sitting here planning the finer/final details of a research project specifically on the role of the feet in body temperature (in relation to sleep).

The reader is correct - feet do have a big impact on body temperature, and more so in sleep.

The feet are ideally suited to helping us keep a stable body temperature, for a few reasons.

They - like the hands - have a large surface area as well as specialised blood vessels which can be opened up to pass high volumes of blood through them and therefore offload heat quickly when required.

When not required, the blood vessels are constricted.

This, coupled with the fact that the feet (and hands) are at the end of our limbs and don't have much muscle (which produces heat) means that they cool down much more than other regions of the body.

So, by using specialised nerves driven by the thermostat in our brain, we can massively change the temperature of our feet to allow our body temperature to be controlled very accurately.

As for the issue of "put socks on and it warms you up immediately"; that's more perception than reality. (Admittedly though, in some ways a person's perception is their reality.)

The feet can become so cool that pain receptors are triggered and so they're uncomfortable; so wrapping and therefore warming them up has an obvious perceptual benefit.

This also underlies the age-old notion that if you're cold, put a hat on. The head loses a relatively large amount of heat even when we're cold, because there's limited scope to naturally insulate it and constrict its blood vessels.

It's also important in determining how comfortable we are with our temperature.

Putting a hat on has a big perceptual and real effect; it also makes the brain's thermostat less inclined to restrict blood flow to our feet, so they won't be so cold and therefore will be more comfortable on a cold day. So, that's not a myth after all.

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