פירוש על נגעים 3:4

השחין המכוה מטמאים בשבוע אחד – for the rest of the plagues have two locking-ups, but if it did not spread during the first week, and a white hair did not appear, he releases him. And the language of מיטמאין/made unclean/impure that it (i.e., the Mishnah) uses, this is what he (i.e., the Mishnah) said: When these two tokens/signs came at the end of one week, but if they didn’t come, he is pure/clean.

A boil or a burn becomes unclean for one week and by one of the following two tokens: by white hair or by a spreading.
By white hair, in the beginning, at the end of the week, or after it has been pronounced clean.
"Or by a spreading:" At the end of the week, or after it had been declared clean. They become unclean for a week which is seven days.
Section one: The Torah mentions a nega found in a boil or a burn (Leviticus 13: 18, 25). But it does not mention a two week period of isolation in connection with such a nega. Therefore, a person can become impure after only one week of isolation. Also, quick flesh is not a sign here, as it was for a nega found on regular skin.
Sections two and three: These are the same as yesterday's mishnah, except there are only two signs and the uncleanness happens after one week, not two.