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 LLLT device for androgenetic alopecia in 2007, recognizing it as safe for consumer use. However, FDA clearance does not confirm equal effectiveness for all individuals, which is an important nuance often overlooked in promotional materials.

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). These wavelengths penetrate the scalp and are absorbed by a mitochondrial enzyme called cytochrome c oxidase, which plays a role in the final stage of cellular respiration. When this enzyme absorbs photons from the laser light, it accelerates ATP production, improving the energy supply available to hair follicle cells.

In a 2013 double-blind, randomized, sham-controlled study published in Lasers in Surgery and Medicine, Dr. Michael R. Hamblin and colleagues tested a 655 nm LLLT comb on 110 men with androgenetic alopecia for 26 weeks. The treatment group experienced an average 35% increase in hair density compared to the placebo group. The study concluded that increased cellular energy and improved follicular metabolism were responsible for the observed effects. However, the sample size was limited, and the study’s funding came from a device manufacturer, raising questions about potential bias.

The key mechanism proposed 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 also appears to increase scalp blood circulation, potentially improving oxygen and nutrient delivery to the follicles. A 2017 randomized, double-blind, sham-controlled study published in the American Journal of Clinical Dermatology evaluated a helmet-type photobiomodulation device on 44 men and 47 women over 16 weeks. Participants receiving active treatment experienced a statistically significant increase in both hair count and hair thickness compared to those using a sham device. The researchers linked this improvement to the upregulation of vascular endothelial growth factor (VEGF), a protein responsible for stimulating new blood vessel formation.

This process, called angiogenesis, could enhance follicle nourishment.

While promising, the study acknowledged that device design, wavelength precision, and treatment frequency greatly affect outcomes. Furthermore, participants’ adherence to the protocol influenced the consistency of results.

Calming the Inflammation That Blocks Growth

Inflammation in the scalp is a less visible but critical factor in hair loss. LLLT may reduce this inflammation by moderating cytokine activity—cytokines are signaling proteins that can either promote or suppress inflammation. In a 2018 in vitro study published in Photobiomodulation, Photomedicine, and Laser Surgery, researchers exposed cultured human dermal papilla cells to 660 nm light. After 24 hours, they observed reduced expression of inflammatory cytokines and increased cell proliferation compared to untreated cells. Although the experiment was performed on cells in a laboratory setting rather than on human subjects, it suggests that LLLT might create a more favorable scalp environment for hair growth.

How Long Before Results Appear?

Most clinical studies report visible changes after three to six months of consistent use. A 2014 multicenter, randomized, sham-controlled trial, also published in the American Journal of Clinical Dermatology, followed 128 men using a 655 nm laser helmet three times weekly for 24 weeks. The treated group showed an average increase of 18 hairs per square centimeter, while the control group lost an average of two hairs per square centimeter, indicate a measurable but moderate improvement. The researchers emphasized that continuous use is required to sustain benefits, as discontinuation often leads to hair shedding and regression of gains.

A Critical Look at the Evidence

Although multiple studies show positive trends, several limitations must be acknowledged. A 2021 review by Gupta and Foley in Lasers in Medical Science analyzed dozens of trials and concluded that while most report statistically significant hair growth, many suffer from methodological issues. These include small sample sizes, short trial durations, inconsistent device parameters, and conflicts of interest from industry funding. Urges caution in interpreting the data, stressing that LLLT’s effectiveness can vary depending on individual biological responses, age, hormonal environment, and treatment consistency.

Current research is moving toward personalized and combination therapies. Studies funded by the National Institutes of Health (NIH) are exploring synergistic protocols that pair LLLT with 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 stimulates hair growth primarily by increasing cellular energy production, enhancing blood circulation, and reducing scalp inflammation. Yet, its effectiveness depends on consistent use, correct wavelength exposure, and individual biological variability. The science supports its potential, but critical evaluation of the evidence shows that results are often modest and uneven.

References

Hamblin, M. R., et al. (2013). Effect of a 655-nm low-level laser therapy on hair growth in men with androgenetic alopecia: A randomized, double-blind, sham device-controlled trial. Lasers in Surgery and Medicine, 45(8), 487–495. Retrieved from https://pubmed.ncbi.nlm.nih.gov/24186905/

Lanzafame, R. J., et al. (2014). The growth of human scalp hair mediated by visible red light laser and LED sources in males. American Journal of Clinical Dermatology, 15(5), 331–337. Retrieved from https://pubmed.ncbi.nlm.nih.gov/25124964/

Lanzafame, R. J., et al. (2017). Safety and efficacy of a novel helmet-type photobiomodulation device for androgenetic alopecia: A randomized, sham-controlled, double-blind study. American Journal of Clinical Dermatology, 18(4), 607–613. Retrieved from https://pubmed.ncbi.nlm.nih.gov/28349575/

Kim, W. S., et al. (2018). Effects of 660 nm low-level laser therapy on human dermal papilla cells: In vitro study. Photobiomodulation, Photomedicine, and Laser Surgery, 36(10), 534–540. Retrieved from https://pubmed.ncbi.nlm.nih.gov/30411479/

Gupta, A. K., & Foley, K. A. (2021). A critical appraisal of low-level laser therapy for hair loss. Lasers in Medical Science, 36(7), 1539–1549. Retrieved from https://pubmed.ncbi.nlm.nih.gov/33738532/

U.S. Food and Drug Administration (FDA). (2007). 510(k) Premarket Notification for HairMax LaserComb. Retrieved from https://www.accessdata.fda.gov/cdrh_docs/pdf7/K070417.pdf