do harm

To do harm is to cause damage or injury. Too much sun on a child's shoulders, a rumour repeated once too often.

It takes to: to your eyes, to her reputation. No article — doing a harm is not English. The phrase lives mostly in negatives and conditionals, which is where a learner will actually meet it: it will do no harm to ask, there is no harm in trying, it never did me any harm. First, do no harm is the doctor's version, and more harm than good is the fixed comparison.

Phrases it lives in

• more harm than good — Damaging on balance, however well meant.