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Why, when I first step into a hot shower, do I get a brief shiver down my back?

David Muir
Edinburgh, UK

There are receptors in your skin that detect pain, pressure, vibration, texture, heat and cold. On occasion, however, they can be confused. Your back has fewer receptors per unit area than most parts of your body, so it is more easily befuddled, even if briefly.

Walk backwards into a hot shower and the water hitting your skin can initially feel cold; walk backwards into a cold shower (masochist!) and it can, for a second, seem hot.

You are experiencing a sensation called the paradoxical response to heat, self-explanatory in its name. This transitory perceptual illusion can become problematic with certain neurological conditions, but it is hardly noticed by most of us. The central mechanism is still not entirely understood.

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