Statisticians are rumoured to say that if you have one foot in a bucket of ice and your other foot in a bucket of boiling water, on average you’re comfortable! I’ll return to this joke later, anyway…
Temperature is not the only thing that influences whether you feel hot or cold.
Your body is designed to operate at a steady state temperature of about 37ºC. The biological processes of life convert food into action and heat energy, so the very act of living is generating heat… that heat threatens to raise your body temperature above the safe range… certainly if your core body temperature goes above 41ºC you’re in trouble.
To combat the heat generated by being alive, your body dumps the excess heat in order to keep the body at that ideal temperature of 37ºC. When your body needs to lose heat fast, it will use mechanisms like sweating to dump that excess heat through evaporation.
Your body is used to a normal rate of losing heat. If you feel hot, that means you are losing heat slower than normal. If you feel cold, that means you are losing heat faster than normal.
So, for example, if your body decides to fight an infection by raising your core body temperature, you will now be losing heat faster than normal and feel cold… even if the room is the same temperature and despite everyone else telling you that you’re running a fever!
Suppose you disagree with your body’s immune system and decide to take a medication to fight the fever, depending on how your body reacts to that medication may even lower your body temperature below the 37ºC and you can end up feeling hot and sweating despite everyone telling you that you feel cold!
There are also external factors that can influence whether you feel hot or cold. The biggest one is humidity. This is related to how your body uses sweating to dump heat. When the air is dry, your body doesn’t need to sweat so much to lose heat because sweat evaporates quickly in dry air. When the air is humid, it is a lot harder to lose heat through evaporation.
This is why a dry heat doesn’t feel as hot as a damp heat. On the other side you can have a damp cold being colder than a dry cold. Irish people can be used to this phenomenon when they go to a really cold place for a winter break. I remember being in Canada in the winter when it was -40º (both C and F are the same when it’s -40º). At that temperature almost all the moisture has been frozen out of the air and standing in the porch in PJs with no wind felt warmer than standing at a bus stop in Ireland wearing hat coat and scarf at 1ºC with the wind blowing!
Now don’t get me wrong, at -40º exposure from the wind is very dangerous, but without wind and without being in contact with a cold surface, your body is not losing heat as quickly as when you’re in damp Ireland with the wind blowing.
Now about that joke poking fun at statisticians and their “on average you’re comfortable”… there is actually a kernel of truth to the joke. If you have one leg colder than the other, your body can use that temperature difference to regulate heat, increasing or decreasing blood flow to either leg. This is why a lot of people sleep with one leg outside the duvet… the problem with the statistician joke is that the temperatures are too extreme.
If you feel hot, that’s your body telling you that it cannot lose heat fast enough.
If you feel cold, that’s your body telling you that it is losing heat too fast.
These marathon runners in Jerusalem below were using foil blankets because during the run their body has gotten used to dumping the excess heat and when they stop running the body doesn’t stop quite so fast, so even in warm Jerusalem they feel cold. The foil blanket reflects the radiative heat lose from their back and keeps them feeling warm.
Hopefully this post has helped you understand the sometimes counter-intuitive way your body perceives temperature a little more. But I’ll stop writing now as I’m feeling cold and need to get up and move!