Mischna zu Wajikra 13:2

The signs of negaim are two which, in fact, are four. The bright spot (baheret) is bright white like snow; secondary to it is the sign as white as the lime of the Temple. The rising (se'et) is as white of the skin of an egg; secondary to it is the like white wool, the words of Rabbi Meir. But the sages say: the rising (se'et) is white wool and secondary to it is like the white of the skin of an egg.

The following places in a person do not become unclean on account of a bright spot: the inside of the eye, the inside of the ear, the inside of the nose and the inside of the mouth, wrinkles, wrinkles in the neck, under the breast and the armpit, the sole of the foot, the nails, the head and the beard; and a boil, a burn and a blister that are festering. All these: Do not become unclean on account of negaim Do not combine with other negaim, A nega is not considered to spread into them, Do not become unclean on account of quick flesh, And they do not act to prevent a person from being considered to have turned completely white. If subsequently a bald spot arose in the head or beard, or if a boil, a burn or a blister formed a scar: They may become unclean by negaim, But they do not combine with other negaim, A nega is not considered to spread into them, And they do not become unclean on account of quick flesh. But they do act to prevent a person from being considered to have all turned white. The head and the beard before they have grown hair, and warts with thin necks on the head or the beard, are treated as the skin of the flesh.

The following bright spots are clean:Those that one had before the Torah was given, Those that a non-Jew had when he converted; Or a child when it was born, Or those that were in a crease and were subsequently uncovered. If they were on the head or the beard, on a boil, a burn or a blister that is festering, and subsequently the head or the beard became bald, and the boil, burn or blister turned into a scar, they are clean. If they were on the head or the beard before they grew hair, and they then grew hair and subsequently became bald, or if they were on the body before the boil, burn or blister before they were festering and then these formed a scar or were healed: Rabbi Eliezer ben Jacob said that they are unclean since at the beginning and at the end they were unclean, But the sages say: they are clean.