DNA evidence can become contaminated when DNA from another source gets mixed with DNA relevant to the case. For this reason, investigators and laboratory personnel should always wear disposable gloves, use clean instruments, and avoid touching other objects, including their own body, when handling evidence.
Environmental factors, such as heat and humidity, can also accelerate the degradation of DNA. For example, wet or moist evidence that is packaged in plastic will provide a growth environment for bacteria that can destroy DNA evidence.
Therefore, biological evidence should be thoroughly air dried, packaged in paper, and properly labeled. Handled in this manner, DNA can be stored for years without risk of extensive degradation, even at room temperature. For long-term storage issues, contact the local crime laboratory.
From Understanding DNA Evidence: A Guide for Victim Serice Providers, May 2001, Brochure, National Institute of Justice and Office for Victims of Crime
