Is self-harm a sin?

[tonychanyt]

I think so.

Idol worshippers cut themselves in 1 Kings 18:

28 So they shouted louder and slashed themselves with swords and spears, as was their custom, until their blood flowed.

A demonized man cut himself in Mark 5:

5 Night and day among the tombs and on the mountains he was always crying out and cutting himself with stones.

As Christians, our body belongs to God, 1 Corinthians 6:

19 Or do you not know that your body is a temple of the Holy Spirit within you, whom you have from God? You are not your own, 20for you were bought with a price. So glorify God in your body.

Self-harming would not glorify God.