What is the origin of the idiom "keep your hair on" and when to use it?

The exact origin of the phrase "keep your hair on" is unclear, but it likely emerged in British English in the early to mid-20th century as a colloquial expression. The phrase is believed to have originated from the idea of someone becoming so agitated or upset that their hair appears disheveled or stands on end. It is often employed in informal conversations, friendly exchanges, or situations where individuals need a gentle reminder to stay calm and composed. This expression can be used in various settings, such as during disagreements, moments of frustration, or when someone is overreacting to a minor issue. It is commonly used among friends, colleagues, or family members to diffuse tension, inject humor, and encourage emotional restraint.