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News|Articles|April 16, 2026 (Updated: April 16, 2026)

Impact of Chemical Hair Straightening on LC-MS/MS-Based Hair Drug Analysis

Author(s)John Chasse
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Key Takeaways

  • Ammonium thioglycolate–based straightening produced a pronounced rise in endogenous GHB, with ~6- to 43-fold increases across temporally matched 0.5-cm hair segments.
  • Alprazolam showed the opposite directionality, decreasing ~1.7- to 2-fold in segments corresponding to the reported dosing period after straightening.
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To investigate how permanent chemical hair straightening influences the accuracy of hair drug testing using liquid chromatography–tandem mass spectrometry (LC-MS/MS), researchers analyzed hair samples before and after treatment with an alkaline straightener (ammonium thioglycolate), measuring levels of the endogenous compound gamma-hydroxybutyrate and the drug alprazolam. The study emphasizes the need for careful interpretation of LC-MS/MS hair analysis results and systematic documentation of cosmetic treatments in forensic and toxicological investigations, particularly when detecting low-level substances.

Testing hair is a common way to check for drugs or chemicals, but everyday hair treatments can change the results. While we already know how bleaching, dyeing, and using a flat iron affect these tests, we still don't know much about the effects of permanent chemical hair straighteners, especially on hair that is actively growing on someone's head. To begin bridging this gap, researchers at the Institute of Forensic Sciences at the University of, Santiago de Compostela (Spain) prepared a case report evaluating the impact of an alkaline-based permanent hair straightening procedure on the determination of an endogenous compound, gamma-hydroxybutyrate (GHB), and an exogenous drug, alprazolam, in hair. GHB was quantified in 0.5-cm hair segments using a validated liquid chromatography-tandem mass spectrometry (LC-MS/MS) method, and alprazolam was analyzed in 2-cm segments using a validated LC-MS/MS method for drugs of abuse and psychoactive pharmaceuticals. A paper based on the researchers’ work was published in Drug Testing and Analysis.1

Understanding the results of a hair test can be tricky because many different factors affect them. Things like a person's hair color, thickness, texture, and the specific drug being looked for all play a role. Additionally, everyday hair treatments can damage the inside of the hair, which makes it much easier for outside chemicals to get trapped and mess up the test results.2-4 While much is known about how bleaching, dyeing, and perming affect hair tests, the research team states that there is very little research on the effects of permanent chemical hair straighteners.1 These treatments have become incredibly popular lately—especially for women with curly, wavy, or frizzy hair—because they keep hair smooth for months and make it much easier to style and manage.5

The hair samples examined in this study were collected from a 39-year-old woman before and 1 month after undergoing chemical hair straightening based on ammonium thioglycolate. Adjacent hair strands corresponding to identical temporal windows were analyzed. All analyzed segments were positive for GHB in both samples. After the straightening procedure, endogenous GHB concentrations showed a pronounced increase compared with pretreatment levels, with fold changes ranging from approximately 6 to 43 in corresponding segments. In contrast, alprazolam concentrations in segments corresponding to the reported period of drug intake decreased by approximately 1.7- to 2-fold following chemical straightening. This case report demonstrates that permanent chemical hair straightening can produce marked and analyte-dependent effects on hair drug concentrations.1

“These findings,” write the authors of the paper,1 “emphasize the importance of systematic documentation of cosmetic hair treatments and careful interpretation of hair analysis results in forensic casework, particularly when analyte concentrations are low.”

The researchers believe that more research is needed on how permanent chemical hair straighteners affect hair drug tests, as very few studies currently exist. To make test results more accurate, testers should always keep a record of the hair products a person uses. This is especially important in cases involving one-time drug use or drug-related crimes, where the traces of drugs left in the hair are already very tiny and hard to detect.1

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References

  1. Blanco-Ces, M.; de-Castro-Ríos, A.; Cobo-Golpe, M. et al. Chemical Straightening as a Source of Analytical Variability in Hair Testing: A Dual-Analyte Case Report. Drug Test Anal. 2026.DOI: 10.1002/dta.70071
  2. Skopp, G.; Pötsch, L.; Moeller, M. R. On Cosmetically Treated Hair--Aspects and Pitfalls of Interpretation. Forensic Sci Int. 1997, 84 (1-3), 43-52. DOI: 10.1016/s0379-0738(96)02047-6
  3. Jurado, C.; Kintz, P.; Menéndez, M. et al. Influence of the Cosmetic Treatment of Hair on Drug Testing. Int J Legal Med. 1997, 110 (3), 159-163. DOI: 10.1007/s004140050056
  4. Gerace, E.; Veronesi, A.; Martra, G. et al. Study of Cocaine Incorporation in Hair Damaged by Cosmetic Treatments. Forensic Chem. 2017, 3, 69–73. DOI: 10.1016/j.forc.2017.02.004.
  5. Miranda-Vilela, A. L.; Botelho, A. J.; Muehlmann, L. A. An Overview of Chemical Straightening of Human hair: Technical Aspects, Potential Risks to Hair Fibre and Health and Legal Issues. Int J Cosmet Sci. 2014, 36 (1), 2-11. DOI: 10.1111/ics.12093

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