In previous times they would say to leave garments out in the sun after washing for a period of time. They would say to not have contact with a person for a period of time, etc etc etc.
This was for coming into contact with anything deemed “unclean”.
This is about DNA. If an animal or blood or something of the sort was made contact with then that DNA would be present on the skin or in the system for a period of time.
We are to purify our DNA. This is important.