“Yahweh spoke to Moses and Aaron. ‘When a person has on the skin of his body a swelling, an eruption, or a spot, and it turns into a leprous disease on the skin of his body, he shall be brought to Aaron the priest or to one of his sons the priests. The priest shall examine the disease on the skin of his body. If the hair in the diseased area has turned white and disease appears to be deeper than the skin of his body, it is a leprous’ disease. After the priest has examined him he shall pronounce him ceremonially unclean. But if the spot is white in the skin of his body, and appears no deeper than the skin, and the hair in it has not turned white, the priest shall confine the diseased person for seven days. The priest shall examine him on the seventh day. If he sees that the disease is checked and the disease has not spread in the skin, then the priest shall confine him seven days more. The priest shall examine him again on the seventh day. If the disease has abated and the disease has not spread in the skin, then the priest shall pronounce him clean. It is only an eruption. He shall wash his clothes and be clean. But if the eruption spreads in the skin, after he has shown himself to the priest for his cleansing, he shall appear again before the priest. The priest shall make an examination. If the eruption has spread in the skin, the priest shall pronounce him unclean. It is a leprous disease.’”
In this case Yahweh spoke to both Moses and Aaron. Aaron and his priestly sons have to act as both doctor and religious leader. They decide who has leprosy and therefore who is unclean and who is not. First, if anyone has a swelling on their body, they have to go the priest to be examined as if he were a medical doctor. The test was if the hair in the diseased area had turned white, the disease had to be more than skin deep. Then they would be declared ceremonially unclean, lepers. However, if it is not deep and the hair had not turned white, they were confined for 7 days. After 7 days and everything looked okay, they were to be confined for another 7 days. Thus after 14 days, they could be declared clean if they washed their clothes. On the other hand, if this eruption had spread, the priest should pronounce them unclean. Being unclean with leprosy meant that you had to be quarantined from the rest of the people.