Leviticus 13:27

13:27 The priest must then examine it on the seventh day, and if it is spreading further on the skin, then the priest is to pronounce him unclean. It is a diseased infection.

Leviticus 13:35-36

13:35 If, however, the scall spreads further on the skin after his purification, 13:36 then the priest is to examine it, and if the scall has spread on the skin the priest is not to search further for reddish yellow hair. The person is unclean.