Parashas Metzora · Passuk 15:19
Chabad.org — English translation + Rashi
Torah Temima points to Toras Kohanim.
English: “And whoever touches her shall be impure” — one might think that one who touches her conveys impurity to a person and to earthenware; Scripture teaches “and whoever touches her shall be impure” [limiting the effect].
Limited impurity of one who touches a niddah
Chazal limit the impurity of one who touches a niddah so that he does not become an av that conveys further to people and earthenware in the same way she does.