Scientists Read Body Clock From a Single Hair

Researchers at Charité – Universitätsmedizin Berlin have developed a method to determine an individual’s internal biological clock using a sample of hair. This new test allows scientists to read a person’s circadian rhythm by analyzing cells from a few hair follicles, providing a simpler alternative to existing diagnostic methods.

The biological clock, or circadian rhythm, is a fundamental system that regulates more than just sleep cycles. It influences a wide array of critical bodily functions, including metabolism, hormone levels, and immune activity. When these rhythms are disrupted, it can negatively impact various systems throughout the body.

The Mechanism of the Hair-Based Test

The new testing method, developed by Achim Kramer and his team, focuses on the transcriptional activity of specific genes within hair follicle cells. By examining these cells, researchers can pinpoint the current state of the biological clock.

The process involves the measurement of 17 different genes that are either part of the molecular clock or are regulated by it. To interpret this complex genetic data and determine the precise biological time, the team utilizes artificial intelligence for analysis.

In these cells, we measure the activity of 17 genes that are part of the molecular clock or are controlled by it

Achim Kramer, Charité—Universitätsmedizin Berlin

According to reporting from EurekAlert on April 1, 2026, the researchers demonstrated that this hair-based test can determine an individual’s circadian rhythm with a level of accuracy that is nearly equivalent to existing standard tests.

Clinical Importance of Circadian Timing

Understanding the timing of the internal clock is increasingly important for the field of circadian medicine. Because every person’s biological clock ticks at a slightly different pace, the time of day can be a critical factor in the success and safety of medical treatments.

One specific example of this is found in cardiac surgery. Research indicates that aortic valve replacements performed in the afternoon are associated with fewer adverse side effects compared to those performed at other times.

By accurately identifying a patient’s biological time, medical providers may be able to better time interventions to align with the body’s natural rhythms, potentially improving patient outcomes and reducing complications.

Comparison to Existing Diagnostic Methods

Prior to the development of the hair follicle test, the most accurate way to determine a person’s internal clock time was through the repeated measurement of melatonin levels in the saliva. This process requires multiple samples to be taken during the hours immediately preceding bedtime.

While accurate, the saliva-based method is difficult to implement outside of a controlled hospital or laboratory environment. The requirement for repeated sampling over several hours makes it impractical for many clinical settings or for patients to perform independently.

The hair-based approach offers a significantly less invasive and more convenient alternative. By requiring only a few strands of hair or cells from the follicles, the test removes the need for repeated sampling over a period of time.

Research Publication and Verification

The findings of this research were published in the Proceedings of the National Academy of Sciences. The study establishes a new pathway for chronobiologists to obtain accurate biological clock readings without the logistical burdens of traditional melatonin testing.

By leveraging the combination of genetic transcriptional activity and artificial intelligence, the team at Charité – Universitätsmedizin Berlin has provided a tool that could expand the practical application of circadian medicine in everyday healthcare.