Leviticus 21:5-6

21:5 Priests must not have a bald spot shaved on their head, they must not shave the corner of their beard, and they must not cut slashes in their body.

21:6 “‘They must be holy to their God, and they must not profane the name of their God, because they are the ones who present the Lord’s gifts, the food of their God. Therefore they must be holy.