štetiti

1. (+ dat.) to harm; to be harmful to
   Pušenje šteti zdravlju. — Smoking harms your health.
   Previše sunca šteti koži. — Too much sun is bad for the skin.
2. (without an object) to hurt; to do harm
   Malo odmora ne bi štetilo. — A little rest wouldn't hurt.

In modern usage it usually takes the dative: štetiti nekome/nečemu; the perfective in this sense is naštetiti. The negated ne bi štetilo means "it wouldn't hurt".