"break into a sweat"

"When faced with standing up in front of a group, we break into a sweat because we are afraid of rejection."
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According to Cambridge Dictionary Online and Newbury House Dictionary, the word sweat is uncountable which means that indefinite article an can't be used before sweat. This site states that "we use the indefinite article, a/an, with count nouns." While I was searching online, I found an idiomatic expression but into doesn’t exist.

However, the preposition into has been added right here. In a word, can I rely on this site because I couldn't find `break into a sweat’ in dictionaries? Is this expression common among English native speakers native English speakers?

Yes, it's an expression.

yes.it is."sweat" in this meaning is countable and usually singular.
he breaks in ti sweat just at the thought of flying.

We also use the plural in some expressions- night sweats/break out in the sweats.

:up: Another fairly common one is 'bring on a sweat' - colloquially ('Just the thought of it brings on a sweat among members of the group'). And, less informally 'induce a sweat' ('The purpose of the treatment was to induce a sweat in the patient' - although I'm sure Ray will have a more impressive word for this: perhaps 'The treatment was sudorigenic ;-)').

b

Quote:

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Originally Posted by death

Yes, it is. "Sweat" in this meaning is countable and usually singular.

He breaks in ti into a sweat just at the thought of flying.

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Death, your profile shows that you are an English teacher. As such, it's important that you stick to the correct standards of written English - capitalisation, punctuation etc. Learners will read your posts and they will assume that they are examples of correct English, so please ensure that they are.

Quote:

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Originally Posted by death

yes.it is."sweat" in this meaning is countable and usually singular.
he breaks in ti sweat just at the thought of flying.

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death, you have been asked at least three times to use capital letters correctly. You cannot expect to be taken seriously as a teacher if you make no effort to write correctly.