I had a conversation with a coworker and he told me to keep my hair on. My first understanding of the idiom was that he will do something so fast that, if I was wearing a wig or something it will fly away. I have checked the meaning and it was to keep calm, not get angry and overreact. I have no idea how I am going to loose my hair if I get angry hence where this idiom comes from?
I have Googled and read something about keep your shirt on was the original expression and came from the days when ordinary man had two shirts and he had to take off his precious shirt before getting in a fight. ( First recorded in the USA in George W. Harris's 1854 book Spirit of the Times: 'I say, you durned ash cats, just keep yer shirts on, will ye?')
Keep your hair on was some sort of humorous development of this, but I still don't get how you are going to lose your hair if you get angry, not that all expressions have to make sense but I find it peculiar. Is it connected with the phrase let your hair down? The phrase comes from the same time period when women had to wear their hair pinned up on the head in public. They were only allowed to let their hair down to hang naturally when alone, either when bathing or at bedtime. The phrase means merely to relax and to go easy.
What is the more popular phrase today that one with the hair or with shirt ? Does it make more sense if the woman use the phrase with hair and men the phrase with shirt ?
Best Answer
Keep one's hair on indeed means
History
As far as I know, it's a colloquial British English idiomatic expression, urging the other party not to lose their cool. However, it seems to have spread across the globe and is widely used across the US, Australia and other English speaking countries.
Acc. to Google Ngrams, the phrase first appears in 1868-69. To keep your shirt on has the same meaning and tone but doesn't seem to appear before 1870-71, according to Google Ngrams and in 1904 according to Etymonline.
NOTE: The expression "keep your hat on" predates them both to the year 1804.
Extended Explanation (Disclaimer: This is some sheer guesswork, putting two and two together.)
The idiom seems to be constructed from that fact that one might lose their hair due to stress (check this), or even might pull it out in exasperation, anger or frustration.
The Ngram results definitely indicate that keep your hair on is currently more popular than keep your shirt on". And for what its worth, these expressions have nothing to do with to let your hair down.