"Leprosy" (as referred to in the Torah) is a condition that makes a patch of skin appear white and sunken. If there is white hair or healed flesh in the patch or it has spread after a seven-day period the person is impure, as it says "If a person has on his skin...".¹ A person also becomes impure if a patch of his hair falls out and thin yellow hair grows in its place or it spreads, as it says "If a man or woman has a condition on the head or on the beard...".² Such persons must be pronounced impure (and when they are healed, pure) by a priest, as it says "And the priests the sons of Levi... by their mouths shall every dispute and every condition be [decided]".³ It is forbidden to disturb the signs of impurity or to shave the bald patch, as it says "And he shall not shave the bald patch",⁴ and it says "Take care for the leprous condition to guard it well and to do as the priests, the Levites teach you; as I have commanded them you shall be careful to do".^5,a

The leper must cover his head and tear his clothes, must not cut his hair or wash his clothes, and must not enter a walled city, as it says "And the leper who has the condition, his clothes shall be torn and his hair grown and he shall cover his mouth... outside the camp shall be his dwelling".⁶ If he touches a person or utensil or stops under the same roof with them or is moved by a person or rests on a suitable object they become impure. When he is healed he must be purified by sprinkling with water in which the blood of a bird has been mixed and a live bird, cedarwood, scarlet wool, and hyssop have been dipped [as it says "This shall be the law of the leper on the day he becomes pure..."].⁷ He must shave off all his hair, bathe, wash his clothes, and wait seven days (during which his touch still makes things impure), after which he shaves, bathes and washes again, and becomes pure.^b

Certain types of greenish or reddish discolorations make a white wool or linen or skin garment or a house (in the land of Israel, outside Jerusalem), impure if they spread or remain for two or three weeks [as it says "And if a garment has in it a leprous condition...",⁸ and it says "If I cause a leprous condition in your house..."⁹]. Such a garment or house is a source of impurity like a leper. When a garment is healed it becomes pure by being washed; when a house is healed it requires a purification ceremony like that of a leper.^c