Ceremonial uncleanness under the law of Moses could be spread from the unclean to the person who came in contact with them. Uncleanliness could be spread.
A tradition grew among the Jews that the altar of the Temple could not be profaned, and that if an unclean person came into contact with it, the altar did not become unclean but instead the person coming into contact with the altar became clean. We have two examples of persons relying upon this tradition in the case of Joab in the Old Testament and Zacharias in the New.
Joab was to be killed by Solomon, and he knew he was to die. To die in contact with the altar was to die clean, and so Joab fled to the tabernacle, took hold of the altar and was killed there. The ones sent to kill him hesitated because they also knew they were killing a clean man, and had to be told a second time to kill him by Solomon. (See, 1 Kings 2: 28-34.) Solomon did not care that Joab would die clean.
In the case of Zacharias, his death is not recorded other than in a passing reference by Christ as He confronted the scribes and Pharisees. (Matt. 23: 35.) Joseph Smith said this reference was to John’s father.
In the case of Christ, the tradition had fulfillment. He touched the unclean, but communicated cleanliness to them. Whether it was the woman with an issue of blood, a leper, or the dead, touching them did not make Him unclean, rather it made those whom He touched clean.