Adam Clarke on Leviticus 13:18

In the skin thereof, was a boil - Scheuchzer supposes this and the following verse to speak of phlegmonic, erysipelatous, gangrenous, and phagedenic ulcers, all of which were subjected to the examination of the priest, to see whether they were infectious, or whether the leprosy might not take its origin from them. A person with any sore or disposition to contagion was more likely to catch the infection by contact with the diseased person, than he was whose skin was whole and sound, and his habit good.