Infrared light is a type of electromagnetic radiation just below what the human eye can detect. Sunlight is one of the largest sources of IR radiation but many other objects around us absorb and emit this frequency of light.
Research shows that infrared light affects the human body in ways beneficial to health when administered under certain conditions. Understanding these conditions can help one decide if products such as infrared saunas or heating pads may be worth the investment.
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Wavelengths of Light
The vast majority of energy in the universe isn’t electromagnetic. Leading scientific theories describe that nearly 95% of all energy in our universe might not be visible at all! Energies such as dark matter are thought to be the majority shareholders in the universal energy market.
The electromagnetic spectrum accounts for only a small fraction of that 5% of the energy that is visible. I’ve read estimates of less than 0.1% but haven’t confirmed to my own satisfaction. Within that tiny fraction, of a tiny fraction, there is an even tinier fraction of light that the human eye can perceive. This is called visible light. Below is a chart displaying the frequencies the average human is able to perceive visually:
Wavelengths of Visible Light (Colors)
| Color Name | Wavelength (nm) |
|---|---|
| Red | 631-728 |
| Orange | 590-617 |
| Yellow | 563-656 |
| Green | 498-558 |
| Blue | 458-496 |
| Indigo | 436-456 |
| Violet | 396-433 |
Note: The figures in the above chart are averages taken from the following sources:
- Howard L. Cohen. AST 1002 Study Guide. The University of Florida, 1999–2003.
- J.L. Morton. Color Matters, 1995–2002.
- A Dictionary of Science. Oxford University Press, 2000.
- Thomas Young. Theory of Light and Colours, 1802.
Types of Infrared Light
Just below red light is a frequency known as the Infrared Spectrum which falls between 700nm – 1000nm in wavelength. Also known as thermal radiation, this light isn’t visible to the human eye. The sun emits infrared light, anything warm emits infrared light, and even humans emit infrared light. IR is everywhere!
The infrared light spectrum is commonly subdivided into 3 smaller sections (R):
- IR-A – Near Infrared (780-1.4nm)
- IR-B – Mid-Infrared (1,400-3,000nm)
- IR-C – Far Infrared (3,000-10,000nm)
NOTE: These figures are from the International Commission on Illumination standards. ISO 20473 IR standards differ slightly.
Each of these ranges affects matter differently and can elicit different effects on the human body. Infrared has been studied since its discovery in the early 1800s by Sir William Herschel. Below is a brief summary of these three bands of IR energy.
Near-Infrared (IR-A, NIR)
Near-infrared light has a wavelength of 700-1,400 nm and is the closest to visible light of all infrared radiation. In the 1970s, researchers accidentally discovered that near-infrared energy accelerated wound healing in mice (R).
More current research has uncovered a more specific understanding of the exact type of cells that respond to near-infrared light (R)(R). This research hints that “photobiomodulation” techniques such as NIR therapy can actually help improve mitochondrial function.
Mid-Infrared (IR-B, MIR)
Mid-infrared light falls in the range of 1,400-3,000nm and has both heating and lighting properties. MIR therapy has been investigated as a potential anticancer therapy (R)(R) and in supporting favorable mitochondrial function (R).
The MIR range of energy seems to fall into a somewhat awkward category in that the majority of health-related IR research focuses on NIR or FIR. That is, at least the majority of the research I’ve read.
Far-Infrared (IR-C, FIR)
Far-Infrared light falls in the range of 3,000-10,000nm and is the only IR range that transfers energy as pure heat (R). FIR radiation is well-absorbed by the human body and can quickly create a rise in temperature.
Medical applications of FIR light include accelerated wound healing by increasing blood flow, improved skin health by the same mechanism, and angiogenesis (new blood vessel formation) (R).
Types of Infrared Light Therapy
Low-Level Laser Therapy (LLLT)
As early as 1901, scientists have been using light to treat various human illnesses (R). Low-Level Laser Therapy is a term coined describing—not the wavelength of light—but, rather, the total power (R). LLLT lasers commonly operate in the NIR range at output ranges of 5mW/cm2 (R).
The duration of treatment ranges from 30 seconds to 60 seconds and is administered in “pulses.” Currently, there are four “clinical targets” for LLLT therapy (R):
- The site of injury to promote healing, remodeling, and reduce inflammation.
- Lymph nodes to reduce edema and inflammation.
- Nerves to induce analgesia.
- Trigger points to reduce tenderness and relax contracted muscle fibers.
As many as 15 separate sites may be targeted during any single treatment phase. The only reported adverse side effects from LLLT therapies are related to eye damage consistent with other types of laser devices. Side effects are statistically similar to placebo when it comes to areas of the body where LLLT devices are being used (arm, lumbar region, etc.) In other words, LLLT therapy is super safe.
Benefits of Infrared Light Therapies
In 1995, NASA investigated the ability of LED light to support plant growth in space. During this study, it was noted that astronauts experienced decreased wound healing times (R). However, this modern study wasn’t the first investigation of the benefits of light therapy. As early as the 1970s, researchers have investigated the effect of specific wavelengths of light on human health (R).
Water is particularly absorptive of infrared light which can lead to rapid increases in temperature. Given the human body is roughly 75% water—that’s an important fact to hang on to. Research suggests the 800-1,400nm NIR band of infrared light is best optimized for absorption by water-containing bodies (R). That’s not to say other bands of IR light won’t work to some degree as well.
Accelerated Wound Healing
Animal studies have shown NIR therapy can help speed up wound healing. This process has been observed to work by facilitating a temporary increase in anti-inflammatory compounds and growth factors (R).
Certain cells called fibroblasts are deeply involved in skin health. They help synthesize collagen, help heal wounds, and help create the necessary ingredients for other essential dermatological processes. Researchers have shown NIR therapy can increase fibroblast concentrations (R).
Improved Mitochondrial Health
Mitochondria are like the batteries of the human cell. They actively create energy in the form of ATP and help use it to drive nearly every process in our bodies.
One of the last stages of ATP production, called oxidative phosphorylation, involves the mitochondria using oxygen. This process is facilitated by an enzyme named cytochrome oxidase (COX). This process is referred to, simply, as cellular respiration.
In a 2008 paper, Dr. Tiina Karu found that near-infrared light was able to activate mitochondrial signaling pathways (R). This application may be useful to help deliver drugs and other compounds directly to the mitochondria with minimal side effects. In the paper’s closing remarks, Dr. Karu notes as such:
Recent experimental data demonstrate that laser phototherapy may facilitate recovery from retinal injuries and other ocular diseases wherein mitochondrial dysfunction is postulated to play a role
Bone Health
Animal studies have shown NIR therapy can help stimulate the formation of new bone structure (R). In-vitro studies have also shown that low-level light therapy (LLLT) may also be able to help avoid the progression of bone-related diseases such as osteoporosis (R).
Another in-vitro study has shown NIR therapy can help heal fractured bones faster (R). This is attributed to immediate increases in intracellular ATP levels following NIR exposure. Currently, there are limited human trials underway to confirm such benefits of NIR on bone healing (R).
Cognitive Therapies
Minerals like calcium play a huge role in regulating how our brain processes information. It regulates when neurotransmitters are being released, helps control neuronal excitability, and has been shown as a pivotal player in helping form long-term memory (R).
NIR therapy has shown the ability to affect the flow of calcium on an intracellular level (R). This has many potential applications in human health, particularly relating to cardiovascular health, but particularly in the brain. NIR therapy may one day be useful to stimulate very specific areas of the brain both for research and therapeutic purposes (R).
It’s important to note that neuronal stimulation via NIR isn’t completely understood. Lack of penetrating power may limit the effectiveness of NIR applications. It’s also theorized that the structured nature of body fluids may allow greater stimulation via infrared energy, thus allowing more efficient neuronal targeting. Researchers believe that NIR may exhibit a hormetic effect on certain areas of the body, specifically the eyes and brain (R).
Final Thoughts
Infrared light makes up only a fraction of the overall spectrum of electromagnetic energy—smaller even the range of visible light. Our eyes can detect this light but its influence on our bodies is unignorable. I suppose the readiness at which the human body responds to infrared light should come as no surprise. After all, natural sunlight is loaded with it! Researchers are still uncovering the potential health benefits of FIR therapy. Products like infrared saunas, heaters, and cold-laser therapies already make use of known medical applications.
