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At least around here, in Costa Rica, it is common practice to avoid drinking cold drinks while drinking hot soup. I never questioned this (but didn't really care about it). Apparently it is, well, bad to mix two different-temperature drinks.

Is there any truth to this?

  • Where is "here"? – Mark Henderson Jan 7 '13 at 4:29
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    Costa Rica, Central America, in the middle of nowhere XD – Dr. Nobody Jan 7 '13 at 4:31
  • This piece of wisdom was also passed on to me, in the UK. And just like the answer given below, the reason told to me was "its bad for your teeth" – Jamiec Jan 7 '13 at 14:40
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Try putting hot water in a glass, empty it and then pour ice cold water in it. It is very likely it will break. The rapid change in temperature causes non-even contractions of the material and makes it break.

This happens to the enamel in your teeth. Although it does not need to break, since the temperature difference is not so extreme, it may weaken the enamel and make it easier for tooth cavities to form.

Here is a scientific paper which explains it more rigorously

http://jdr.sagepub.com/content/51/2/461.abstract

Abstract as follows:

This paper presents the results of experiments conducted with extracted human and bovine teeth. The teeth were subjected to thermal cycling at temperatures between 140 and 90 F. The results offer conclusive evidence that thermal fracture may be induced by the thermal stresses caused by the temperature cycling. Less than 3,000 thermal cycles cause severe cracking or the propagation of cracks previously existing in the teeth, or both.

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    I wonder...would the results be as significant if they did a study of the effects on teeth in live subjects instead of on extracted teeth? I know they're compositionally the same, but nature is full of surprises. – called2voyage Apr 29 '16 at 19:20
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    I don't have access to the full text of this paper at the moment. From the abstract, they varied temperature from 90°F to 140°F. Did the damage occur at all temperatures? Because a typical hot soup is going to be nowhere near 140°F when it enters the mouth. Also, the papers that cite this one suggest that the teeth were held at the temperature for at least 50 seconds, whereas a person eating soup would only have the hot liquid against their teeth for a fraction of that time. – ESultanik Sep 7 '16 at 12:34

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