According to a report by West Virginia University, 93% of human hairs examined provide mtDNA information that may be used to determine factors related to DNA testing. 1. 1.0 cm of hair is usually all that is required for successful testing. 2. Hair that is up to 30 years old with no significant environmental damage will usually be effective. 3. Rate of heteroplasmy is about 9-14%. When testing is done on the roots rather than the actual hair, hair DNA testing success rate is independent of cosmetic hair treatments, structure of the medulla, length of the hair shaft, hair diameter, volume or scalp origin.