Summary: Are you a morning person or a night owl? Your hair can reveal the answer. Researchers have developed HairTime, a noninvasive diagnostic that estimates an individual’s chronotype from a few hair follicles. By measuring the activity of 17 key genes in the hair root, the test maps a person’s circadian phase without lengthy laboratory melatonin measurements.
Applied to more than 4,000 participants, the method confirms that age, sex, and genetics influence internal timing, but it also shows that lifestyle and work schedules have a larger effect than previously recognized.
Key Facts
- 17-Gene Signature: HairTime analyzes a pattern of 17 genes in hair follicle cells—genes that make up or respond to the molecular clock—to estimate internal time.
- Lifestyle vs. Genetics: Employed people showed circadian phases about 30 minutes earlier on average than non-employed participants, highlighting the influence of social schedules on biology.
- Gender Differences: Women’s biological night began on average about six minutes earlier than men’s—a modest but statistically significant difference.
- Age-Related Shift: People in their mid-20s tended to be alert roughly one hour later than those over 50, confirming known age-related shifts in timing.
- Clinical Potential: The test supports the development of circadian medicine, enabling treatments—such as cancer immunotherapies or blood pressure drugs—to be timed to when they will work best for each patient.
Source: Charité
Overview
A research team at Charité – Universitätsmedizin Berlin has introduced HairTime, a hair-based assay that estimates a person’s circadian phase from cells taken from a few hair follicles. The developers intend the test to support circadian medicine—healthcare that accounts for each person’s internal clock when diagnosing and planning treatment.
Circadian rhythms affect sleep, metabolism, immune function, and how medications work. Traditional assessment of internal time relies on dim-light melatonin onset (DLMO), a reliable but time-consuming laboratory procedure that measures melatonin in saliva over several hours. HairTime offers a simpler, scalable alternative.
How the test works
The assay measures the expression of 17 genes in hair follicle cells—genes that either form part of the molecular clock or are controlled by it. Using machine learning, the researchers convert this gene-expression pattern into an estimate of the person’s current circadian phase. A single daytime hair sample is sufficient.
In validation studies, HairTime predicted circadian phase with accuracy comparable to DLMO. Because collecting hair is easy and suitable for at-home sampling, the method is practical for large-scale research and clinical use.
What the large-sample analysis revealed
The team analyzed roughly 4,000 hair samples submitted by individuals at home. The results confirmed established patterns—such as the delay in timing observed in younger adults—but also produced some new insights. The gender difference in biological night start was smaller than previous questionnaire-based estimates, at about six minutes earlier for women. More strikingly, employment status correlated with a 30-minute earlier internal time in working people, showing how daily routines and social cues can shift clock-gene expression.
Overall, chronotype is shaped by multiple influences: genetic predisposition, age, sex, and lifestyle. Because these factors interact, individuals can have widely different internal times even if they share the same external schedule.
Implications for medicine
By enabling straightforward, biologically based assessment of circadian phase, HairTime moves circadian medicine closer to routine clinical practice. Standardizing the assay for diagnostic laboratories is the next step so it can be used for sleep counseling, diagnosing irregular sleep–wake rhythms, and ultimately for timing therapies to improve effectiveness and reduce side effects.
About the study and commercialization
Parts of this research were conducted within the Collaborative Research Center “Foundations of Circadian Medicine” (TRR 418), funded by the German Research Foundation. BodyClock Technologies GmbH, a Charité spin-off co-founded by one of the study’s lead researchers, contributed to data collection for the approximately 4,000 samples analyzed. The researchers report no additions to the scientific findings beyond the published study.
Key Questions Answered:
A: Self-reports are subjective and can be influenced by caffeine, stress, or social obligations. HairTime measures actual gene activity, revealing the body’s molecular time, which can differ from how alert you feel. Knowing true circadian phase is important for targeted medical decisions, such as timing treatments when the immune system is most active.
Q: Can changing my job change my chronotype?
A: Yes. The study found that work schedules shift internal timing: employed participants had clocks about 30 minutes earlier than non-employed participants. This suggests daily routines and social cues can modulate clock-gene expression over time.
Q: How does this help with jet lag or time changes?
A: Many people experience “social jet lag,” a mismatch between social schedules and internal timing. HairTime can help diagnose irregular sleep–wake rhythms and guide personalized sleep counseling or light therapy to better align daily life with biological time.
Editorial Notes:
- Article edited by Neuroscience News staff.
- Journal paper reviewed in full by editors.
- Additional context provided by the editorial team.
About this circadian rhythm research news
Author: Markus Heggen
Source: Charité
Contact: Markus Heggen – Charité
Image: Image credited to Neuroscience News
Original Research: “HairTime: A noninvasive assay for estimating circadian phase from a single hair sample” by Bert Maier, Luísa K. Pilz, Selin Özcakir, Ali Rahjouei, Ashraf N. Abdo, Jan de Zeeuw, Dieter Kunz, and Achim Kramer. PNAS. DOI: 10.1073/pnas.2514928123
Abstract
Circadian clocks coordinate daily physiology and behavior and are essential for health; disruptions increase disease risk. The circadian phase of entrainment—the timing of the internal clock relative to environmental cycles—varies across individuals and is influenced by genetic and environmental factors. Traditional DLMO measurement is impractical for large studies, and blood-based molecular markers have limitations.
HairTime estimates circadian phase from a single daytime hair sample. Developed and validated in training and validation cohorts, the assay showed strong agreement with DLMO and proved suitable for large-scale application. Analysis of more than 4,000 samples found normally distributed circadian phase estimates associated with age, sex, and notably, work schedules, indicating societal factors can alter internal timing. These results support HairTime as a practical tool for research and a foundation for personalized chronotherapy.