Sforno on Leviticus 13:2/ספורנו על ויקרא י״ג:ב׳

1אדם כי יהיה בעור בשרו, generally, such phenomena occur when one did not purify oneself from the effects of having had sexual relations or direct contact with the seed of a menstruating woman.

2שאת או ספחת או בהרת, different skin afflictions, the common denominator being that they are of different shades of white. We base ourselves on the oral tradition as spelled out in Nega-im 1,1. None of these phenomena correspond to the skin diseases we read about in medical text books. Such phenomena as are mentioned in these textbooks do not result in the afflicted person being considered ritually impure, nor are they subject to the priest deciding if indeed the symptoms require isolation of the afflicted person and when such symptoms can be declared as having disappeared. According to Berachot 5 the only skin afflictions which may be viewed as G’d’s reminder to improve our lifestyle are the four kinds mentioned in our chapter. While they are not classified as afflictions revealing G’d’s love for the person thus afflicted, they are however, described as מזבח כפרה, as “an altar serving as stepping stone to atonement for the character weakness that the afflicted person has to overcome.” G’d does not employ any other medically well known skin diseases as His instrument to call us to order for various sins committed. והובא, anyone who goes to a place to be attended to is not referred to as “coming,” בא, but as being brought, i.e. הובא. Compare Psalms 45,15. The passive mode of the transitive form והגישו אדוניו in Exodus 21,6 is ונגשו אל המשפט, “he his being brought to.”