Dirty hands is a metaphor used in moral and political philosophy and everyday conversation to symbolize the sullying of one's moral standing by dealing with unsavory matters. The idea conveyed is that in handling messy situations, it is impossible to come away clean.
The expression comes from Jean-Paul Sartre's 1948 play Dirty Hands, in which Hoederer speaks of having hands dirty up to his elbows, and asks, "So what? Do you think one can govern innocently?" The play describes actions that violate moral principles, but which are purportedly carried out in the interests of the greater good.
A related saying is "sometimes you have to get your hands dirty," meaning detachment from difficult situations is not always possible. There is also the saying that someone "has blood on their hands", implicating or accusing a person of being an enabler or passive participant in wrongdoing, and that a person "washes one's hands of" something, meaning a person disavows responsibility for something.
Sissela Bok writes that Machiavelli maintains in The Prince that rulers who cling to moral principles in order to avoid dirty hands, no matter the cost, are weak and invariably end up defeated, a view opposed by Erasmus and Kant.[1]