Timing of Radiation Therapy May Influence Hair Loss

More than 12 million Americans suffer with cancer, according to reports by the American Cancer Society. For many, radiation therapy is an effective method of preventing the spread of cancerous cells while also working to eliminate them entirely. Radiation therapy is known to harm healthy cells, however, which may cause a variety of side effects including hair loss.

For patients who experience hair loss during radiation therapy, new research suggests administering the treatment later in the day might mitigate such side effects. Scientists hope the study will provide a foundation for future research on further managing the toxic side effects of radiation therapy. For patients, the study provides hope that the unwanted side effects of cancer treatment, like hair loss, can be mitigated.

Managing the Toxic Effects of Radiation Therapy

Nearly half of all cancer patients will encounter radiation therapy as part of their treatment protocol, according to the National Cancer Institute (i). For some, radiation therapy is an effective means of managing, and ultimately killing, cancerous cells. Radiation therapy comes with a price, however.

Radiation therapy exposes the body to large amounts of high-energy radiation like x-rays, gamma rays, and other charged particles. These particles course through the patient’s body, seeking to shrink and kill cancer cells. Radiation cannot distinguish between cancer cells and healthy ones, however, and modern medicine has not yet developed a way to effectively hyper-target radiation to specific malignant cells. As a result, healthy cells are often killed along with cancerous ones.

Researchers from USC, the Salk Institute for Biological Studies, and the University of California, Irvine (UCI) believe the toxic side effects of radiation therapy can be managed, however. Published in the Proceedings of the National Academy of Sciences, their study evaluated the hair loss experienced by laboratory mice following radiation therapy at different times of day. Specifically, mice that received early morning radiation therapy lost approximately 85% of their body hair, whereas those treated later in the day lost as little as 17% (ii).

Researchers say the difference in hair loss is due to the circadian rhythm of the hair cells themselves. Most commonly referred to as an internal clock, the circadian rhythm of individual cells determines when biological processes are active (awake) or subdued (asleep). In the study above, researchers found the hair circadian rhythm of the mice to be inactive in the mornings and active in the evenings, a pattern that might account for the substantial difference in the hair loss exhibited by each test group.

Satchidananda Panda, co-lead investigator and associate professor in Salk’s Regulatory Biology Laboratory, explains (iii):

“Delivering a drug to an organ while it is largely inactive is not a good idea. You could do more damage to the organ than when it is awake, repairing and restoring itself. If you know when an organ is mending itself, you might be able to deliver more potent doses of a drug or therapy. That might offer a better outcome while minimizing side effects.”

This health report has been produced by the Hair Transplant Institute of Miami. For additional information on our Institute, including hair loss evaluation and consultation services, readers are invited to contact our office directly at 1-877-443-9070.


(i) “Radiation Therapy for Cancer.” National Cancer Institute. Accessed 30 May 2013.

(ii) “Timing of Radiation Therapy May Minimize Hair Loss.” Health Canal. Accessed 30 May 2013.

(iii) See above.