Komentarz do Negaim 5:1

כל ספק נגעים חוץ מזה – [this relates to Chapter 4, Mishnah 11 towards the end of the Mishnah] – that the doubt regarding the bright white spot in the flesh preceded [or] the doubt about whether the white hair preceded.

Any doubtful nega is regarded as clean, except this case and one other. In general, in a doubtful case concerning a nega, meaning it is unclear whether it is or is not a nega, the affected person is considered clean. However, there are two exceptions. The first is the case we saw in yesterday's mishnah (4:11) and the second case is in this mishnah.

הרי היא כסלע – it became as wide and as large as a Sela.

Which is that? If he had a bright spot of the size of a split bean and he was isolated, and by the end of the week it was as big as a sela, and it is doubtful whether it is the original one or whether another came in its place, he must be regarded as unclean. Originally, the nega was the size of a split bean. This is large enough to cause him to be isolated for a week to see if it spreads or if white hairs appear. By the end of the first week, the nega is the size of a sela, a coin which is much larger than a split bean. It is unclear whether this is the original nega and it just spread or if it is a new nega. If it is a new nega, he would start a new period of isolation. However, in this case the halakhah is strict and we consider the original nega to have spread, causing him to be impure.

ספק היא היא – and it is worthy/fit [for the person] to be declared a certified leper, for it spread.

ספק שאחרת באה תחתיה – that the first went away/disappeared and he is fit to be shut up/isolated, for spreading does not defile at the outset.

ומחליטו – and he declares him to be a certified leper.