How Does Low-Level Laser Therapy Actually Stimulate Hair Growth?

Low-Level Laser Therapy (LLLT), sometimes called red light therapy or cold laser therapy, is frequently promoted as a non-invasive method for treating hair loss. While the concept of using light to regrow hair may sound speculative, its mechanism has been investigated for decades in clinical and experimental studies.

The U.S. Food and Drug Administration (FDA) cleared the first laser comb for men in January 2007 through the 510(k) process, which finds a device substantially equivalent to one already on the market. Devices are FDA-cleared, not FDA-approved. Clearance does not show that a device works equally well for everyone.

Most home devices use Class 3R lasers. The FDA says lasers in this class can be momentarily hazardous to the eye when a person looks directly into the beam, so do not look into the light or point it at the eyes.

The Science Behind the Beam

To understand how LLLT might stimulate hair growth, we must begin with its biological target: the mitochondria. These are the organelles within cells responsible for producing adenosine triphosphate (ATP), the molecule that fuels nearly every cellular process. LLLT devices usually emit light between 630 and 680 nanometers (visible red light) or 780 to 850 nanometers (near-infrared light). The leading hypothesis is that these wavelengths reach the follicles and are absorbed by a mitochondrial enzyme called cytochrome c oxidase, which plays a role in the final stage of cellular respiration, and that this raises ATP production in hair follicle cells. This has not been measured directly in human scalp trials.

In a 2013 double-blind, randomized, sham-controlled study published in Lasers in Surgery and Medicine, Lanzafame and colleagues tested a 655 nm laser-and-LED helmet on 44 men with androgenetic alopecia for 16 weeks. After one outlier was excluded, the active group had a 35% greater increase in hair counts than the sham group. The study measured hair counts, not cellular energy. In a separate 2009 sham-controlled trial of the HairMax LaserComb (Leavitt et al., Clinical Drug Investigation), 110 men completed 26 weeks, and the laser group had a significantly greater increase in terminal hair density than the sham group. Both trials were small.

One proposed mechanism is that energized follicles can re-enter the anagen phase, the active growth stage of the hair cycle. Many people with androgenetic alopecia have follicles trapped in the telogen (resting) phase, and photostimulation may help restart their growth.

Improved Blood Flow and Follicular Nourishment

LLLT is also proposed to increase scalp blood circulation, potentially improving oxygen and nutrient delivery to the follicles. This has not been confirmed in the hair trials described on this page.

A 2014 double-blind, sham-controlled trial by the same group (Lanzafame et al., Lasers in Surgery and Medicine) tested the same 655 nm helmet in 47 women for 16 weeks. The active group had a 37% greater increase in hair counts than the sham group, and no adverse events were reported. The trial measured hair counts only; it did not measure blood flow.

Calming the Inflammation That Blocks Growth

Some researchers think low-grade scalp inflammation contributes to some types of hair loss. LLLT may reduce this inflammation by moderating cytokine activity—cytokines are signaling proteins that can either promote or suppress inflammation. This is a hypothesis; the trials described here did not measure scalp inflammation.

How Long Before Results Appear?

Most clinical studies report visible changes after three to six months of consistent use. A 2014 multicenter, randomized, sham device-controlled, double-blind study in the American Journal of Clinical Dermatology (Jimenez et al.) randomized 128 men and 141 women to a HairMax Lasercomb (one of three models) or a sham device, used on the whole scalp three times a week for 26 weeks. Among those analyzed, terminal hair counts rose by 18.4 to 25.7 hairs per cm² in the lasercomb groups and by 1.6 to 9.4 hairs per cm² in the sham groups. No serious adverse events were reported. The authors called for further studies of long-term effects and hair maintenance; the trial did not test what happens after stopping.

A Critical Look at the Evidence

Although multiple studies show positive trends, several limitations must be acknowledged. A 2017 systematic review in Lasers in Surgery and Medicine (Afifi et al.) looked at 11 studies with 680 patients. Nine of the 11 studies that measured hair count or density reported statistically significant improvement, and the authors said the findings should be interpreted with caution. Many trials were small and short, and devices differ in wavelength, power and treatment schedule.

Researchers are also interested in combining LLLT with other treatments such as platelet-rich plasma (PRP) or topical minoxidil. Researchers are also studying different light frequencies and pulse durations to determine which cellular pathways respond most strongly to photobiomodulation the scientific term for therapeutic light stimulation. These directions suggest that while LLLT is not a miracle cure, it may become part of a broader, evidence-based approach to managing hair loss.

In short, Low-Level Laser Therapy is thought to act mainly by increasing cellular energy production in follicle cells, and possibly by improving blood flow and reducing inflammation; these mechanisms are not proven in people. Yet, its effectiveness depends on consistent use, correct wavelength exposure, and individual biological variability. Sham-controlled trials report gains in hair counts, but critical evaluation of the evidence shows that results are often modest and uneven.

References

Lanzafame, R. J., Blanche, R. R., Bodian, A. B., Chiacchierini, R. P., Fernandez-Obregon, A., Kazmirek, E. R. (2013). The growth of human scalp hair mediated by visible red light laser and LED sources in males. Lasers in Surgery and Medicine, 45(8), 487–495. https://pubmed.ncbi.nlm.nih.gov/24078483/

Leavitt, M., Charles, G., Heyman, E., & Michaels, D. (2009). HairMax LaserComb laser phototherapy device in the treatment of male androgenetic alopecia: a randomized, double-blind, sham device-controlled, multicentre trial. Clinical Drug Investigation, 29(5), 283–292. https://pubmed.ncbi.nlm.nih.gov/19366270/

Lanzafame, R. J., Blanche, R. R., Chiacchierini, R. P., Kazmirek, E. R., & Sklar, J. A. (2014). The growth of human scalp hair in females using visible red light laser and LED sources. Lasers in Surgery and Medicine, 46(8), 601–607. https://pubmed.ncbi.nlm.nih.gov/25124964/

Jimenez, J. J., Wikramanayake, T. C., Bergfeld, W., Hordinsky, M., Hickman, J. G., Hamblin, M. R., et al. (2014). Efficacy and safety of a low-level laser device in the treatment of male and female pattern hair loss: a multicenter, randomized, sham device-controlled, double-blind study. American Journal of Clinical Dermatology, 15(2), 115–127. https://pubmed.ncbi.nlm.nih.gov/24474647/

Afifi, L., Maranda, E. L., Zarei, M., et al. (2017). Low-level laser therapy as a treatment for androgenetic alopecia. Lasers in Surgery and Medicine, 49(1), 27–39. https://pubmed.ncbi.nlm.nih.gov/27114071/

U.S. Food and Drug Administration. 510(k) K060305, HairMax LaserComb (Lexington International), decision 18 January 2007, substantially equivalent; product code OAP. https://www.accessdata.fda.gov/scripts/cdrh/cfdocs/cfpmn/pmn.cfm?ID=K060305

U.S. Food and Drug Administration. Laser Products and Instruments. https://www.fda.gov/radiation-emitting-products/home-business-and-entertainment-products/laser-products-and-instruments