Which Wavelength of Light is Best for Hair Growth?
In this controlled study of 68 people, 1550 nm and 650 nm light worked best, each adding about 15 hairs per square centimeter over nine months, while far-infrared (14,000 nm) added about 6. All three wavelengths improved hair growth compared with no treatment.
Over nine months, hair density rose from 100 to 114 hairs per square centimeter with 650 nm, from 99 to 115 with 1550 nm, and from 101 to 107 with far-infrared. In the untreated control group it fell from 100 to 98.
Red light therapy, also known as low-level laser therapy (LLLT) or photobiomodulation (PBM), uses specific wavelengths of red and near-infrared light to promote healing and reduce inflammation.
Commercial laser and light devices for hair loss have a known limitation: they typically offer only one wavelength, deliver inconsistent energy, and produce variable results. While 650 nm red light has been extensively studied for hair growth, research on other wavelengths like 1550 nm and far-infrared radiation has been limited. This study directly compared three wavelengths to see how they stack up.
What the Research Shows
Sixty-eight participants between 18 and 60 years old were assigned to one of four groups: 650 nm light, 1550 nm light, 14,000 nm far-infrared radiation, or a control group. Treatments lasted three months, with maintenance sessions every four to six weeks for up to nine months. The researchers assessed hair density, scalp condition, and hair loss at baseline and throughout the study. All three treatment wavelengths showed improvements in hair density and scalp health compared to baseline and the control group. This suggests that the biological mechanisms underlying light-stimulated hair growth may operate across a broader range of wavelengths than previously understood.
Dr. Kumar’s Take
This study is interesting because it challenges the assumption that only red light around 650 nm works for hair loss. The fact that far-infrared radiation at 14,000 nm also showed improvements opens up new possibilities for device design. Each of these wavelengths interacts with tissues differently, and they may be stimulating hair growth through different but complementary pathways. Wavelength did seem to matter here: far-infrared produced less than half the gain of the other two. 1550 nm edged out 650 nm (a gain of 16 versus 14 hairs per square centimeter), but that gap is small. Since 650 nm has the most research behind it, it remains a solid default choice.
What Different Wavelengths Do
Red light at 650 nm is highly absorbed by cells near the skin surface, making it well suited for targeting hair follicles in the scalp. The 1550 nm wavelength is strongly absorbed by water in the skin, so most of its energy stays in the upper layers of tissue. Far-infrared radiation at 14,000 nm interacts with the body primarily through heat energy and may improve scalp circulation through a different mechanism. The fact that all three showed benefit suggests that hair follicle health responds to multiple types of light stimulation, not just one.
Practical Takeaways
- All three tested wavelengths (650 nm, 1550 nm, and 14,000 nm) improved hair density and scalp health in this clinical trial.
- The 650 nm wavelength has the most published research supporting it and remains a reliable choice.
- Every group followed the same schedule: three months of treatment, then maintenance sessions every four to six weeks for up to nine months.
- Wavelength made a difference: 1550 nm (+16 hairs/cm²) and 650 nm (+14) outperformed far-infrared (+6), while the untreated group lost 2.
FAQs
If all wavelengths work, why do most devices use 650 nm?
Mostly because red light has the longest research record. The FDA clearance of devices like the HairMax LaserComb was based on studies using this wavelength. Other wavelengths may be equally effective but have less clinical trial data supporting them.
How often should I use a light therapy device for hair growth?
In this study, participants received treatments over three months with maintenance sessions every four to six weeks afterward. Most evidence supports using light therapy devices at least three to five days per week for initial treatment, then reducing frequency for maintenance once results are established.
Can I combine different wavelengths for better results?
The study tested each wavelength independently, so it did not directly assess combinations. However, many commercial panels and helmets already combine red and near-infrared wavelengths. Based on the finding that different wavelengths may stimulate hair growth through different pathways, a multi-wavelength approach could theoretically be beneficial, though this needs further study.
Bottom Line
This controlled study suggests that light therapy at multiple wavelengths can improve hair density and scalp health. In this study, 1550 nm and 650 nm gave the largest gains in hair density, and far-infrared gave a smaller one. With the longest research record, 650 nm remains a solid default, and 1550 nm looks like a promising alternative.
