What is the different between primary transfer and secondary transfer in human hair?

Primary and secondary transfer can occur with both humans and animals. Primary transfer occurs when a person's or animal's hair is lost or shed directly on to a surface (clothing, furniture, a car) Secondary transfer occurs when shed hair is "picked up" from its primary deposition site and transported to another location. An example of this can be if a dog sheds hair onto a couch because he was sitting there (primary transfer) and then a person sits on the couch, gets the dog hair on his clothes and goes home. The hair he collected on his clothes is shed in his car on the way home (secondary transfer). The dog was never in the car, but because of secondary transfer, its fur will be. This can help establish movement throughout a house or prove a person was at a certain location during the commission of a crime for forensic trace examiners.