וְרָאָ֣ה הַכֹּהֵ֗ן וְהִנֵּ֤ה מַרְאֶ֙הָ֙ שָׁפָ֣ל מִן־הָע֔וֹר וּשְׂעָרָ֖הּ הָפַ֣ךְ לָבָ֑ן וְטִמְּא֧וֹ הַכֹּהֵ֛ן נֶֽגַע־צָרַ֥עַת הִ֖וא בַּשְּׁחִ֥ין פָּרָֽחָה׃
And the priest shall look; and, behold, if the appearance thereof be lower than the skin, and the hair thereof be turned white, then the priest shall pronounce him unclean: it is the plague of leprosy, it hath broken out in the boil.
Read halakhic rulings (Jewish law) on Leviticus 13:20 from the Mishneh Torah and classical halakhic sources, free online.