A person typically loses about 100 hairs a day. These hairs may be of evidentiary value to show contact between two people. With an adequate hair standard, a trace chemist will be able to microscopically compare an unknown hair to a standard collection and determine if the unknown hair could have come from the individual under investigation. Hair comparisons can not identify a hair as coming from one individual to the exclusion of anyone else. DNA testing can strengthen any possible association of the hairs.

Hair shaft
Human head hair with attached tissue indicating the hair was forcefully removed from the scalp.
Human Hairs Microscopical comparison of two human head hairs