I would assume it has something to do with body hair. If so, does it change anything for more hairy or less hairy humans?
In: Biology
Normal skin temperature for healthy adults ranges between 33⁰-37⁰ C. Being in 30⁰ C water still means that you are losing your body heat. Air is a much worser heat conductor than water, which means you are not losing your body heat **fast enough**.
Water can transmit heat extremely well.
So, the water feels colder, because the heat from your body is taken away much faster than air can do.
Difference in enthalpy. Water can absorb and hold more thermal energy than air. This is also why a sauna won’t cook you, at least not very fast.
It’s a matter of thermal conductivity.
Cold and hot sensations actually depend on wether your skin is heating up or cooling down, you don’t really feel temperature like a thermometer.
Your body is 37 °C, water at 30 °C will sap away heat from your body fast, since it conducts heat very well. Air on the other hand conducts it much worse, so it can’t sap heat from your skin faster than your body produces heat.
The feeling of hot or cold is more to do with the *rate* at which energy is being transferred. The faster the energy is wicked away from the body (or towards) the colder or hotter (respectively) it feels. Air is a poor conductor, water much better, copper even more so.
You don’t feel temperature, you feel whether a body part is gaining or losing heat. Cold = losing heat, hot = gaining heat.
Water has a much higher specific heat capacity than air so heat dissipates through it much faster than through air, so in water you lose more heat than in air if the air/water is at a lower temperature than you.
Water can full heat away from your body about 800 times faster than air. The same temperature difference between you and the water will pull a lot more heat out of you than if it’s you vs air.
This is the same reason why there is a maximum safe time to sit in a hot tub. You can sit out all day in 104° air. You’ll be uncomfortable, but if you have enough water, you’ll be OK. A 104° hot tub, is a different story.
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