Leviticus 13:25

Then the priest shall look upon it: and, behold, if the hair in the bright spot be turned white, and it be in sight deeper than the skin; it is a leprosy broken out of the burning: wherefore the priest shall pronounce him unclean: it is the plague of leprosy.

Cross-reference

Leviticus 13:4 requires isolation if hair is not white and spot not deeper—contrasting with the leprosy diagnosis here when those signs appear.

Leviticus 13:18-20 handles a healed boil turning leprous—parallel examination process and criteria as for the burn here.