Tazria-Metzora-The laws of ritual impurity and purity-Rabbi Yakira
To pronounce a fellow Jew as impure is an enormous responsibility only a Kohen, who is chosen to bless the people with love, can make such a declaration, as it will be accepted as the honest truth. In biblical times, Tzaraat, was a punishment for lashon hara (gossip), and had to be inspected by a Kohen. Tzaraat is a super-natural plague, which amazingly can also afflict garments.