No skin off my back (also used as no skin off my nose) is an idiom that is used when somebody wants to express that it makes no difference to them what someone else does or thinks.
The expression can also relate to situations that have a negative outcome but don’t affect the user.
Here is an example of no skin off my back used in a sentence: “She can mess up her own career, it’s totally up to her, no skin off my back.”
The expression is believed to have originated from working-class people in the United Kingdom, during the early-20th century. It was a common phenomenon among coal miners to bruise their back during work, upon crawling in low mineshafts, which practically “took the skin off their backs”.
Another theory suggests that no skin off my back stems from even earlier times, dating back to times when slavery and whipping as a punishment was still in practice in Europe. It is possible that the idiom stemmed from situations where individuals showed disinterest about obeying orders, even if that meant losing skin off their backs due to whipping.
No skin off my back is a commonly used expression in the United Kingdom to this day. However, throughout the 20th century, many other derivatives for the expression came to existence.
In the United States, the term is most commonly used as “no skin off my nose”, but “no skin off me” and “no skin off my bugle” also exist. A very commonly used expression that conveys a similar meaning is “no use crying over spilled milk.”