A hair sample can be used for genetic analysis, but the success of the DNA test depends entirely on the specific part of the hair collected. Standard individual identification, such as paternity or forensic testing, requires the presence of the hair root, or follicular tag, which contains the necessary cellular material. A simple strand of hair that has been cut or shed typically lacks this cellular material, making it unsuitable for the most common types of DNA testing.
The Critical Component of Hair for DNA Testing
The key difference between a usable and an unusable hair sample lies in the presence of the hair root, often visible as a tiny, translucent bulb at the end of a forcibly removed strand. This root is where the hair’s growth occurs and is the only part that contains living cells rich in nuclear deoxyribonucleic acid (DNA). Nuclear DNA is the genetic material found in the cell’s nucleus, inherited from both parents, and is used to definitively identify an individual for purposes like paternity testing.
The hair shaft, the long, visible portion of the hair, consists primarily of keratin, a hard protein made up of dead cells. While the shaft does not contain nuclear DNA, it does contain mitochondrial DNA (mtDNA), found in the mitochondria outside the cell nucleus. Because mtDNA is inherited exclusively from the mother, it cannot distinguish between individuals who share a maternal lineage, making it less informative for individual identification. Therefore, hair that has been shed naturally or cut is often rejected for standard tests requiring nuclear DNA.
Collecting Samples for Accurate Results
Obtaining a high-quality hair sample requires careful attention to the collection method, as the goal is to secure the hair with the follicular tag intact. The hair must be firmly and swiftly pulled from the scalp, rather than clipped or cut, to ensure the root and its surrounding tissue remain attached. Typically, seven to ten hairs with visible root bulbs are required to provide sufficient genetic material for reliable testing.
Once collected, the sample must be handled minimally to prevent contamination and degradation. The root end should not be touched by bare hands; clean tools, such as tweezers, should be used for manipulation. The hairs should then be placed into a clean, breathable paper envelope, which helps absorb residual moisture that could promote mold or bacteria growth. Storing the sample in a plastic bag should be avoided unless specified by the lab, as plastic traps moisture and accelerates DNA degradation.
Factors Affecting Test Success and Reliability
Even with a properly collected sample containing the hair root, various external factors can compromise the success of the DNA test. Chemical treatments, such as hair dyes, bleaches, and perms, introduce harsh chemicals like hydrogen peroxide that damage the DNA structure. These substances accelerate the degradation of the genetic material, reducing the viable DNA that can be extracted and analyzed.
The integrity of the sample is also susceptible to environmental exposure and the age of the hair. DNA degrades rapidly when exposed to moisture, heat, or direct sunlight, which causes the DNA molecule to break down. Samples that have been stored for a long time or found in an unprotected outdoor environment will have a lower yield of recoverable DNA compared to freshly collected hair.
Contamination is a major concern that can lead to inaccurate or inconclusive results. This occurs when genetic material from another source, such as skin cells from the person collecting the sample or foreign particles, mixes with the target hair. Proper handling protocols, including the use of clean tools and protective measures during collection, are necessary to minimize the risk of transferring foreign DNA to the sample.