Or HaChaim on Leviticus 13:44/אור החיים על ויקרא י״ג:מ״ד

1 צרוע הוא טמא הוא, he is "leprous," he is ritually impure. It appears best to approach these words in the same way Hillel approached the words טהור הוא וטהרו הכהן in verse 37. Here the force of the exegesis is even more convincing as the word צרוע refers to the body of the afflicted person whereas we still require that the priest declare him to be ritually impure. This means that legally speaking, his symptoms notwithstanding, the afflicted person would not be considered subject to the laws of impurity until the priest had declared him to be impure.

2The reason the Torah repeated טמא הוא is to make it clear that if the priest had erred and had declared a person as ritually impure although his symptoms did not justify this, the priest's declaration is invalid. The reason the Torah also repeated טמא יטמאנו is explained in Torat Kohanim as including all other categories of ritual impurity. A person never becomes legally impure due to symptoms on his skin unless the priest has declared him to be so.

3צרוע הוא, he is "leprous." Why does the Torah not use the expression צרעת הוא in order to describe the affliction as it has done repeatedly? Perhaps the Torah wanted to indicate G'd's extreme displeasure with a person whom He has afflicted with this disease in such exposed areas of the skin of the head and beard. Most other afflictions listed in our portion occur in more private parts of the body. Generally speaking, G'd displays great concern for the sensitivities of a person even when He punishes him. The person described here as צרוע has forfeited the consideration G'd normally shows even to sinners; this is why he is described as a "leper" throughout. The words בראשו נגעו that his affliction is already in his head, is the justification for calling him a צרוע.