Leviticus 13:34-37

On the seventh day he will examine the sore again. If it has not spread and appears to be no more than skin-deep, the priest will pronounce the person ceremonially clean. The person’s clothing must be washed, and the person will be ceremonially clean. But if the scabby sore begins to spread after the person is pronounced clean, the priest must do another examination. If he finds that the sore has spread, the priest does not need to look for yellow hair. The infected person is ceremonially unclean. But if the color of the scabby sore does not change and black hair has grown on it, it has healed. The priest will then pronounce the person ceremonially clean.