Leviticus 13:6

And the priest shall look on him again. — If, on further examination at the end of another week, the priest finds that the bright spot looks darker, and that it has not spread, he is to pronounce the patient clean, and set him at liberty, since it was simply an ordinary scurf; but though not leprous, the eruption indicated some impurity in his blood, and he had therefore to wash his garments.