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Red Laser Therapy for Hair Growth: Behind the science

Red Laser Therapy for Hair Growth: Behind the science

When it comes to hair loss, any new and modern method can seem like a potential silver bullet in the fight for our follicles. Low-level laser therapy (LLLT) is one of the newest technologies on the block promising to solve hair loss by wearing a device outfitted with red laser diodes or LEDs for a few minutes each day. Can it really be that simple, and how does it work? We’ve got you covered below.

Low-Level Laser Therapy: How does it work?

Science review: What is light, anyway?

From our everyday experiences, we know that there are different types of radiation—but what is radiation? In this case, we’re talking about electromagnetic radiation, from radio waves to sunlight to X-rays. In scientific terms, electromagnetic radiation means any and all frequencies that make up the electromagnetic spectrum and carried by the photon as the quantal unit. The key terms to remember when talking about electromagnetic radiation are:

  • Frequency: The number of waves that pass through a given point per unit of time.
  • Wavelength: The distance between two crests—or troughs—of a wave.
  • Speed of light: The universal speed limit, 299,792,458 meters per second. Nothing can go faster than that!

You don’t need to be a physicist to understand how low-level laser therapy (LLLT) using a product like the Capillus laser cap works, but knowing a bit of the lingo can certainly help break down a complex, yet simple, medical device and gauge whether it could be right for you and your personal haircare goals.

electromagnetic spectrum

At its most basic level, LLLT involves using a light source to supply photons—the quantum particle of electromagnetic radiation—to the skin in order to achieve an intended effect. Light sources, like LEDs inside the laser cap, provide the photons in order to penetrate the skin and stimulate hair growth. These light sources can be coherent, like a laser that emits photons at a single frequency and spectral wavelength, or incoherent, like an LED that emits photons in a narrow enough, but not singular, spectral range. In a medical device meant to generate light, this difference can be important: Not all light sources and wavelengths can penetrate the skin equally, and the difference in cost between laser diodes and LEDs can be substantial. For a product costing hundreds to thousands of dollars, the light source is both the most critical and most expensive component of the therapeutic device. Unfortunately, the research on which type of light source is optimal isn’t definitive, so it’s unclear whether a lower cost LED-based version of a LLLT device is less effective, or if a premium laser-based version is a wasteful upsell.

Visible light—in all the colors of the rainbow—is just one of many types of electromagnetic radiation that we encounter on a daily basis, but it represents an extremely narrow band of the entire electromagnetic spectrum. Radio waves are one common type of electromagnetic radiation—if you listen to the radio in the car, the number in the name of the station being played corresponds to the frequency of the signal. For example, 102.7 KIIS-FM, an FM radio station in Los Angeles, broadcasts its signal at a frequency of 102.7 MHz, while WCBS Newsradio 880, an AM radio station in New York, broadcasts its signal at a frequency of 880 kHz.

If you’ve ever reheated your leftovers in a microwave, you’re already familiar with another type of radiation: microwaves! The spectral range for microwaves encompasses 3-30GHz, with most conventional microwave ovens using the frequency 2.45GHz. If you’ve ever set up a wireless network to connect to the internet, you’ve probably noticed the multiple versions of your home network that end with 2.4GHz or 5GHz—those numbers are referring to the frequency of the WiFi signal. If you’ve ever noticed WiFi issues while using your microwave, it’s possibly due to the interference and overlap between the signals in the 2.4GHz range.

red light application in low-level laser therapy for hair growth

Now that we’ve gotten you up to speed, how are these features applied to physical therapies and treatments? Low-level laser therapy—also known more generally as photobiomodulation, since not all therapies use laser diodes—was stumbled upon by Hungarian physician Endre Mester in the 1960s. Attempting to use lasers to treat cancerous tumors via ablation (i.e. vaporizing them with energy from the laser beam), Mester applied the beam from a ruby laser to the shaved backs of mice. Mester noticed that hair coincidentally began to grow on the patches of skin that had been irradiated by the laser beam, and that increasing the intensity of the laser failed to increase the amount of hair growth that was observed. Subsequent experiments demonstrated that the low-intensity laser light appeared to stimulate wound healing, and non-ablative, low-level laser therapy was born.

absorption and scattering of red light

Image adapted from Zhou et al.¹

It’s unclear why, exactly, LLLT works in the way that it does. Revisiting the common types of electromagnetic radiation, there are two additional key terms to consider: absorption and penetration.

  • Absorption: The ability of a medium, like skin tissue, to take up electromagnetic radiation and transfer the energy from the photons into another form, like thermal or chemical energy.
  • Penetration: The ability of electromagnetic radiation to penetrate past the surface of a medium. Often referred to in the context of penetration depth, or how deeply the radiation can penetrate past the surface before its field has decayed to 1/e, or about 37%, of its original value.

If you’ve ever gotten an X-ray, that’s an example of a type of electromagnetic radiation that can penetrate easily through the skin and soft tissue, but not through tissues like bone or denser materials like lead.

Ultraviolet, or UV, radiation is another type that can penetrate living tissues—though not as easily as X-rays—and is responsible for sunburns and accumulated skin damage that can lead to skin cancer.

Visible light—the light that we can see—has a wavelength that falls between 400-700 nanometers. Red light is closer to 700nm, with infrared beyond that wavelength, while violet light is closer to 400nm with ultraviolet light falling beyond that. If you’ve ever seen your shadow, you know that visible light doesn’t completely penetrate through the body—but that doesn’t mean that light doesn’t penetrate the surface of our skin at all. In the near infrared portion of the spectrum, or from 650-1000nm, light penetrates up to 5mm into the skin, deep enough to reach the hair follicle and the relevant structures surrounding it.

It’s thought that the low-level light in the near infrared spectrum that’s able to penetrate the skin at necessary depth is able to interact with structures known as mitochondrial chromophores and photoacceptors. One such example is cytochrome C oxidase (CCO), an important enzyme that functions as one of the last steps of generating cellular energy in the form of ATP. Near infrared radiation is thought to prevent the association of a chemical, nitric oxide (NO), that typically interacts with CCO to inhibit the generation of ATP. Other chemicals known as reactive oxygen species (ROS) that are produced as a byproduct of ATP production act as signaling molecules for other parts of the cell, and it’s posited that LLLT might be able to impact the expression of genes related to cellular growth and proliferation on a larger scale within the tissue by modifying this mechanism.

near infrared light mitochondrion

Image adapted from Giordano et al.²

LLLT: What is the controversy?

Uncertainty surrounding the underlying mechanisms

As we’ve hinted at before, there’s a lot of uncertainty regarding the exact mechanisms of LLLT. When the mechanism isn’t fully understood, it’s difficult to understand how to optimize the different parameters—like light source, wavelength, intensity, or duration of use—that generate the best outcomes. When the recommended wavelength falls within 600-1070nm and the recommended power of the light source between 1-1000mW, all depending on the application and treatment plan, it isn’t hard to conclude that the technology and treatment might not be fully mature and ready for primetime as a commercial product.

This isn’t to say that positive results aren’t possible: Empirical evidence suggests that near infrared light, in a percentage of cases involving patients with a darker skin tone, can lead to hair hypertrichosis, the clinical term for increased hair growth. Ample evidence suggests that at the very least, near infrared light can lead to increased wound healing, which bears an underlying similarity to the process of hair regrowth and stimulation of the hair follicle itself.

From our research leading to the discovery of ProCelinyl™, increased proliferation of the dermal papilla cells within the hair follicle can be a major factor in promoting hair growth. Keeping in mind that research suggests the average follicle depth on the scalp is 4.16mm—and revisiting the fact that near infrared radiation can penetrate the skin to this depth—the basic principles of LLLT and a medical device like a laser cap seem to add up.

Empirical evidence supports results, but the studies are less than compelling and aren’t always independent from vested financial interests

From what we’ve discussed, the use of LLLT for hair regrowth seems like an overall net positive, even if it represents an uncertain treatment. What are the drawbacks?

When conducting an experiment or undergoing a treatment, having a broad range of parameters and settings at your disposal can be a bit of a double-edged sword. Having the freedom to design devices to utilize wavelengths of light within a 470nm-wide band grants flexibility in reaching different depths of the skin. Varying the power source and the resulting intensity of the light being felt on the skin means that biomedical engineers have yet another knob to turn when designing their devices.

From a different perspective, however, this flexibility can easily be interpreted as uncertainty: Having a wide range of tools is only useful if we truly understand how to put them to use. Even the support team for a prominent brand, when answering a question about frequency of use with their laser cap, answered that the treatment protocol of 6 minutes per day used in the clinical trials generated the best results. Rather than conveying the possible dangers of overuse to discourage overzealous customers, they allude to an outdated rule in pharmacology and allude to only the potential for diminishing returns, or more vaguely, “the opposite effect.” 

In one study using laser therapy helmets, a not-insignificant proportion of the 15 women assigned the helmet reported scalp irritation (4/15), tenderness (6/15), warm sensation on the skin (4/15), and initial shedding (9/15). Though this compared somewhat favorably to two other groups of 15 women using a topical solution of 5% minoxidil or a combination of minoxidil and a laser therapy helmet, the sample sizes are small enough for the differences to be less than compelling. 

This is to say, if using LLLT as prescribed can lead to irritation and negative side effects, overuse may only exacerbate those symptoms without the potential of improved results.

low light laser therapy for hair growth

LLLT products operate in the legal gray area and aren’t FDA-approved

The scientific evidence is encouraging, but the lack of specificity regarding the underlying mechanisms behind LLLT means that it fails to stand up to the rigor of FDA-approved products like minoxidil and finasteride. This segues to another source of controversy regarding LLLT and its many products: They aren’t FDA-approved for the treatment of hair loss. Though some companies may imply differently, the use of low-level lasers for hair regrowth is only FDA cleared.

FDA-approval vs. FDA-clearance

Why is that important? As we’ve detailed in other pieces on the process of FDA approval, rigorous clinical testing and expensive longitudinal human trials are required to gain FDA approval for treating a particular indication like hair loss. This high barrier of entry helps to keep consumers safe and maintain public confidence in commercial products, but also keeps smaller companies with innovative products that may be equally safe and effective from being marketed as treatments.

In medical devices, depending on the class of the device (either I, II, or III, with I being more superficial like a bandage and III generally being the most serious and substantial like a pacemaker or breast implant) and the intended usage, a company may only need to submit a cursory premarket notification to the FDA that the device is “substantially equivalent” in function to previously approved technology, known as the “predicate”. According to a legal firm that specializes in medical device litigation, 93% of devices fall into the Class I category and are exempt from premarket review, while most Class II devices may require premarket notification via a 510(k) form, rather than explicit approval.

Hair laser caps that use LLLT fall into the category of products that only warrant premarket notification. Does this imply that their efficacy is any less impressive? Not necessarily. However, it does feed into a narrative that laser caps and LLLT for hair regrowth are scientifically inconclusive. If laser caps generated results significant enough to draw public and private attention, regulatory scrutiny and subsequent investment into clearing the bar for FDA approval of the medical device would likely follow.

So what's the bottom line with laser therapy for hair growth?

Laser therapy for hair loss is an emerging treatment that seems to be supported by a developing body of scientific evidence. Though laser therapy leads to results in a percentage of patients, the understanding of why those results emerge remains vague and unclear. If the laser therapy products themselves didn’t retail for a sizable cost, this lack of certainty might be easy to overlook as long as the product was reasonably priced and without significant drawbacks.

That’s what makes evaluating laser therapy in this context challenging: Burgeoning scientific research can mean potential new opportunities for treatments that push the bounds of what we previously had available, but the challenge in pinning down the specifics of the treatment and the parameters of the device means that the space is ripe for reckless cost-cutting on one hand and predatory upselling on the other. Either way, this can lead to general profiteering at the expense of a community that’s already feeling vulnerable to begin with. 

If you’re considering investing in a device for low-level laser therapy, make sure that you weigh the pros and cons with your doctor. They may have crucial insight and expertise about particular products, or they may be able to refer you to a specialist in dermatology who does. However, as summer approaches, it seems apt to describe the field of laser therapy for hair loss as a beach marked by a sign saying “NO LIFEGUARD ON DUTY.” Our advice? Dip into the water of LLLT for hair regrowth carefully (and at your own risk).

  1. Zhou, Zijian & Song, Jibin & Nie, Liming & Chen, Xiaoyuan. (2016). Reactive oxygen species generating systems meeting challenges of photodynamic cancer therapy. Chemical Society reviews. 45. 10.1039/c6cs00271d.
  2. Giordano, James & Bikson, Marom & Kappenman, Emily & Clark, Vincent & Coslett, H. & Hamblin, Michael & Hamilton, Roy & Jankord, Ryan & Kozumbo, Walter & Mckinley, R. & Nitsche, Michael & Reilly, J. & Richardson, Jessica & Wurzman, Rachel & Calabrese, Edward. (2017). Mechanisms and Effects of Transcranial Direct Current Stimulation. Dose-Response. 15. 155932581668546. 10.1177/1559325816685467.
Profile photo for Evan Zhao

Reviewed by: Evan Zhao, PhD

Evan is a synthetic biologist and chemical engineer. He completed his BS from Caltech, and his MA and PhD from Princeton University. He received the prestigious Schmidt Science Fellowship as a postdoctoral fellow at MIT/Harvard and has published in the world's top scientific journals including Nature, Nature Biotechnology, Nature Chemical Biology, and more.

Written by: Revela Editorial Team

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