Why is it after your hands touch extremely hot water, cold water then feels hot for a few seconds before feeling the true temperature?


Had this happen after not realizing the water was set to H. Turned on the C and gut reaction pulled my hand away because it thought the water was still hot, when it was already cold.

In: 4

Heat can’t just disappear.

When you touch something hot, and immediately cool with something cold, you sort of ‘trap’ the heat in your skin. Of course your skin also passes the heat on to the passing water, cooling down gradually and letting you feel the true temperature of the water.

Side note, if you burn yourself, don’t use cold water. Use lukewarm water and have it flow across the burn. Cold water will cool the top layer of your skin, but the heat will be trapped deeper. If you use still water (like dunking your hand in a bucket) you’ll just heat the water around your hand and create a layer of insulation.

When you touch something extremely hot, like hot water, it activates special receptors in your skin called thermoreceptors. These receptors send signals to your brain to let it know that something hot is touching your skin.

When you quickly switch from hot water to cold water, the thermoreceptors continue sending signals to your brain, but now they are saying that the temperature is changing from hot to cold. However, your brain doesn’t immediately adjust its perception of temperature. It takes a few seconds for your brain to catch up and understand that the water is now cold.

During these few seconds, your brain still interprets the signals from the thermoreceptors as indicating a hot temperature. So, even though the water is actually cold, your brain perceives it as hot for a short period of time.

This phenomenon is called after-sensation, and it happens because the thermoreceptors need a little time to adjust and accurately communicate the new temperature to your brain. It’s similar to when you look at a bright light and then look away – you might still see an afterimage of the light for a few moments before it fades away.

Eventually, your brain catches up and you start to feel the water’s true temperature.