How can hot water feel cold for a split second then you feel how hot it actually is
In: Biology
I answered a similar question over a year ago, so I will paste my comment below.
So this is called paradoxical cold sensation. It’s a well known phenomenon but the underlying mechanism remains debated.
So we have nerve endings all over our body underneath the skin. These nerve endings have all sorts of receptors attached to them or to a cell that activates them. These receptors function as sensors. We have voltage, temperature (hot and cold), mechanical (stroke, vibration, pressure, tension, etc), osmolarity (osmoreceptors), etc etc sensors all over our body. The temperature receptors called thermoreceptors are found on these nerve endings, once temperature around them crosses a threshold, it activates the receptor which is followed by a signal to your brain. Some receptors make you feel hot, some cold and some pain. Pain or nociception comes from extreme temperatures, above a very particular threshold.
This effect youre seeing shows that under scalding heat, your cold sensation is active. Hence the paradox. There is still heavy debate on why this happens but there are some hypotheses emerging based on the evidence. Some think this is a malfunction, because extreme cold and extreme heat receptors activate the same neurons, so your brain gets an electrical signal and it doesn’t know if this means this is too hot or too cold, it just knows it’s painful. This doesn’t explain why we feel cold though. Another says that cold receptors function as dual sensors, they sense cold, and they sense extreme heat. And this is the receptor itself, the protein. This is supported by the fact a LOT more cold receptors exist under our skin than hot. And then this hypothesis goes on to claim your brain uses information from both to interpret pain, so you get hot but not extremely hot, you feel hot. You get extremely hot, you activate cold and hot, and so you get a transient signal of cold followed by heat pain, the cold signal actual travels much faster to your brain, so that can explain why it’s transient and precedes the heat pain.
The other thing is, we know that paradoxical cold sensation only occurs due to some cold receptors. We also know, whether you experience it or not, depends on your body temperature. So if you’re body temp is hot, say 38, then a less cold signal than usual will feel just as cold (20 degrees Celsius may have felt normal before but with high body temp it feels cold).
Bottom line is, it’s either a crosstalk between hot and cold sensation or it’s a phenomenon caused by cold receptors also sensing extreme heat and sending a cold sensation signal just before the scalding heat signal reaches. We don’t know and we want to know.
Fun fact: paradoxical heat sensation also exists. Which in my opinion favors the hypothesis with crosstalk. Both hypotheses have merit, we really need more studies.
Because our nerves and the way we feel (and experience) things is mostly relative. With the extreme hot feeling cold v/v, the first flash of sensation overloads the receptors. So you can accurately surmise that you felt “cold”, but it’s like a false-positive based on our nerves/brain/our etc limitations of interpreting signals.
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