Amazing Samples: New Growth in the Analysis of Hair’s Structure, DNA, and Stress Correlation

Posted by on Jan 8, 2015 9:45:00 AM


Many different cultures have stories related to special qualities of hair, from strength (the biblical story of Samson), to escape (the Germanic tale of Rapunzel), to even divine appeasement (the Inuit legend of Sedna).

Through science, we have begun to realize a different kind of power that is found in hair: information. From longitudinal studies and biomarker research to forensics and archeology, hair is playing an important role in the continually expanding sphere of human knowledge. Our previous post in the Amazing Samples blog series discussed the discoveries made from urine.  For this blog post, let’s brush up on the value of hair.

Amazing Samples : Hair Analysis

The Structure of Hair

As most of us might remember from our earliest biology lessons, hair is mostly composed of keratin in the form of dead, hardened keratinocytes (a type of skin cell), the same building block as some other “dead cell” materials like fingernails, claws, and hooves. This keratin matrix has a high affinity for many biomarkers, including toxins, vitamins, and hormones. Unfortunately, the cornification process that the cells undergo effectively destroys the DNA they once contained, which explains why only freshly plucked hairs are suitable for DNA analysis.

Depleted DNA vs. Amplified Biomarkers

As little as 30 years ago, DNA analysis from hair seemed beyond our reach due to the fact that a successful DNA analysis requires nuclear DNA.  Only the hair root still contains intact nuclear DNA and the chance of a successful DNA analysis from naturally shed or cut hair is very low—and highly overestimated in most criminal fiction.  However, hair retains significant amounts of mitochondrial DNA, and as testing techniques improve, hair continues to offer the promise of additional genetic data (Read more on hair structure and DNA viability in this article from Forensic Magazine

Conversely, part of the value of hair is its simplicity, as the lack of cell organelles and genetic material can make the captured biomarkers more apparent. Additionally, hair provides a timeline—a chronological record of repeated and/or intermittent exposure(s) that show up as bands of biomarker concentrations along the length of a strand.  This is why hair is collected for longitudinal studies, and is the characteristic used by forensic specialists to identify poisoning.  It was this unique quality of hair that allowed Spargo and Pounds to discover that Isaac Newton’s late-life “derangement of the intellect” was due to shockingly high levels of mercury (

Subtle Signs of Stress

High levels of stress are known to be a leading cause in a wide range of illnesses, generally weakening the body in various ways. Cortisol is the most typically analyzed biomarker, being the primary hormone that physiologically defines stress. While snapshots of an individual’s cortisol levels can easily be taken from bodily fluids, observing and monitoring chronic stress requires multiple collections, which complicates research and potentially adds to the patient’s stress!  Enter the afore-mentioned timeline that hair provides.

Only a few years ago, hair cortisol levels were shown to be a reliable biomarker for long-term stress analysis (, eliminating many of the data collection issues such studies might encounter. As an example, one such study of a group of Swedish university students showed a significant correlation between major life events and the levels of cortisol in their hair, indicating that hair biosamples have great potential value for both public health studies and clinical research (

Hair’s Environment—Bacterial Metagenomics

Up to now, keratin’s affinity for various biomarkers has supplied the primary value of hair for forensic analysis. However, just this year an Australian study has discovered that hair’s microbiome can also provide useful information, specifically pubic hair. Among the subjects, who provided trimmings in three different rounds, the number of microbial strains was high enough and diverse enough to function as a manner of identification, but not so high to make such analysis cumbersome. And as the microbiome is present on the entire shaft of the hair, it does not require the root of the hair, as for analysis of DNA.

Additionally, the microbiomes of two romantically involved, cohabitating individuals had shifted for the third collection, which was within 24 hours of their having intercourse, most likely due to cross-transference of bacterial strains. As this phenomenon had never been observed in previous studies, this observation opens the door to researching the potential use of pubic microbiomes as forensic evidence of sexual assault, supplementing, if not eliminating, more invasive elements of the currently-used sexual assault evidence collection kits. (Read the full study here -  


Are you collecting hair as part of your work or study? If so, what are you looking for? Use the comments section below to share your story, and discuss how hair is an amazing sample! 

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