Tzara’at is a spiritual malady with a physical manifestation. It is sometimes called leprosy but this appears to be a mistranslation. One of the manifestations of tzara’at is that it also affects garments, not just skin. In addition, tzara’at also affects buildings.

The commentary of Ramban (Rabbi Moshe ben Nachman, 1194-1270) discusses the phenomenon of tzara’at in clothes. In a further assault on translating tzara’at as leprosy, he writes that tzara’at on clothes is not something found in nature at all. Neither are any of the other tzara’ot (plural) that afflict people or houses found in nature.

Rather, tzara’at is of a spiritual nature, a sign that a sin has been committed. The placing of the tzara’at indicated what the sin has been. This level of connection to and awareness of G-d is extremely high and therefore the tzara’at of houses only affected homes in the Eretz Yisrael (Land of Israel) where this connection and awareness are far stronger than in the Galut (Diaspora). This occurance in Israel alone is not because of anything intrinsic physically to the Eretz Yisrael but rather because the Eretz Yisrael is the place where G-d’s providence is more clearly displayed.

Ramban continues that tzara’at of houses only started in Biblical times once Bnei Yisrael (the children of Israel) had won control over Eretz Yisrael and lived there in tranquillity. These are the optimum physical conditions in Eretz Yisrael for realising the special connection and awareness of G-d.

Ramban suggests that tzara’at of clothes also only took place in Eretz Yisrael, for similar reasons as to why tzara’at of houses only took place in Eretz Yisrael. Furthermore, tzara’at only afflicted white garments, not coloured garments. This was to show even more clearly that tzara’at was a spiritual malady, not something which arose due to the mixture of colours in a coloured garment.

For more information as to the purpose of tzara’at and when it could strike, see the commentaries at the beginning of perek (chapter) 13 or Sefer Vayikra (the book of Leviticus).