Sifra #1: To teach us that the Din of P'richah applies even if the Nega covers the body is stages. ¹

Sifra #2: To teach us that the Din of P'richah applies even if it appears on the body from top to bottom - and not from the bottom upwards, in the way that a plant grows. ²

Sifra #3: To teach us that the Din of P'richah applies even if it grows on the body from a Tahor location on to a Tamei one ³ and not specifically from a Tamei location on to a Tahor one.

Sifra: To teach us that the Din P'richah extends to all the different kinds of Nega'im - and not exclusively to Se'eis. ¹

Sifra: To preclude a Bohak from the the Din of P'richah, even though it is a Siman of Taharah - like healthy flesh.

Ramban: Theyt imply that the Tzara'as covers the area that was initially stricken plus the rest of the body from head to foot - from which we can extrapolate that if the initial area that was stricken turns into a Bohak ¹ or heals completely, the Metzora is Tamei. ²

Sifra: they imply that the P'richah only needs to cover the parts of the body that are subject to Nega'im - to preclude the location of a 'rebellious boil' or 'a rebellious burn'. ³

Sifra: To preclude the head and the legs themselves from the Din of P'richah - "me'Rosho", 've'Lo Rosho; "Ad Raglav", 've'Lo Raglav'.

Rashi: To preclude a Kohen with impaired eyesight from examining Nega'im. ¹

Sifra): To preclude concealed parts of the body (Such as the underarm). ² The Mishnah in Nega'im, 2:4 explains how men and women pose for the inspection, and we are not concerned for what cannot be seen when they are in in that position.

Nega'im, 3:3: To preclude a Kohen who is blind even in only one eye and a Kohen whose eyesight is poor. ³

Moshav Zekenim #1: Because, when the Nega spreads, it does not enter the flesh deeply, and it is only when it does not spread over the entire body that it consumes and descends. ¹

Moshav Zekenim #2: Because when one's entire body is covered with Tzara'as, everyone knows about it, and it is not necessary to announce it. ²

Because nobody can be totally Tamei. (Heard from R. Aharon Lopiansky.)

Oznayim la'Torah #1: Even though this Din is a Chok (that has no logical explanation), one may suggest that it is because, seeing as number of limbs and sinews of a person correspond to the number of Mitzvos Asei and Lo Sa'aseh, respedctively, and Hashem strikes a person on the limb with which he sinned, there is no such Jew who is devoid of Mitzvos, and who does not possess at leadst one limb that is without sin. Consequently, it is clear that, if a Jew who is stricken on all his limbs, the Tzara'as is not the spiritual illness that the Parshah is discussing, but the physical ailment of leprosy. ³

Oznayim la'Torah #2: The purpose of Tzara'as is to cause the Metzora to do Tehuvsah through which he will atone for his sin. If the Tzara'as has spread to his whole body, he is considered like dead - a Kaparah in itself, and he needs no further actions to atttwain it. ⁴

Perhaps a woman expert in Nega'im sees, and tells the Kohen what to say. The Rambam (Hilchos Tum'as Tzara'as 9:2) says that if a Kohen does not know, a Chacham may examine the Nega and instruct the Kohen to say 'Tahor' or 'Tamei' (PF).

Tiferes Yisrael (2:4:24): Only the Nega is exposed; the rest of her body is covered. ¹

We can use a boy ² who is younger than nine, who is not subject to Hirhur that will brng him to Tum'ah (PF). In fact, the G'riz (in Nazir, 57b DH 'Tosfos' permits a Kohen Katan to see Nega'im. ³