Keep your shirt on and keep your hair on are two idioms that mean the same thing, though one is a British phrase and one is an American phrase. We will examine the definition of the phrases keep your shirt on and keep your hair on, where these expressions came from and some examples of their use in sentences.
To keep your shirt on means to stay calm, to be patient, to refrain from panicking or losing one’s temper. The idiom keep your shirt on is most often used as an admonition. First used in the mid-1800s, keep your shirt on is an American term that most probably stems from the fact that at that time, most men only owned one or perhaps two shirts. Before taking part in an altercation, a man would remove his shirt in order to spare it from being ruined or soiled. The act of removing one’s shirt would serve as a signal that a situation was becoming heated. Telling someone to keep his shirt on indicated a de-escalation of tension.
To keep your hair on also means to stay calm, to be patient, to refrain from panicking or losing one’s temper. The idiom keep your hair on is used as an admonition. First used in the mid-1800s, keep your hair on is a British term that most probably stems from the fact that at one time, British gentlemen wore wigs. It was not uncommon for a man wearing a wig to tear it from his head in a fit of anger and trample it underfoot. However, men stopped wearing wigs in the late eighteenth century and the idiom to keep your hair on did not appear until the mid-nineteenth century. For this reason, another theory is that the phrase is an allusion to tearing one’s hair out in frustration.
It’s hard to keep your shirt on if you have to get something off your chest. (The Chicago Sun-Times)
By the way, we’re about to get to the wildebeest, so please if at all possible keep your shirt on. (The Dallas Observer)
“Keep your hair on. It’s an accident and the insurance is going to pay, if you have insurance that’s it.” (The Daily Star)