Light therapy, also known as photobiomodulation (PBM), is a non-invasive treatment method using specific wavelengths of light to stimulate physiological processes in the body. Among the various types of light therapy, red light (RL) and near-infrared light (NIR) are the most widely used for therapeutic purposes. While they are often grouped together due to their similar mechanisms of action, they differ significantly in wavelength, depth of penetration, biological effects, and clinical applications. This article provides a detailed scientific comparison between red light and near-infrared light therapy, highlighting their respective roles in health and medicine.
1. Wavelength and Physical Properties
Red light typically refers to wavelengths in the range of 620–700 nm, with the most commonly used being 630 nm and 660 nm. In contrast, near-infrared light spans a broader range, from 700 to 1200 nm, with 810 nm, 850 nm, and 940 nm being frequently used in clinical settings (Hamblin, 2017). The key difference between these wavelengths lies in their penetration depth. Red light penetrates tissues up to approximately 5–10 mm, making it suitable for superficial applications.
2. Mechanisms of Action
Both red and near-infrared light exert their effects primarily through the absorption of photons by mitochondrial chromophores, especially cytochrome c oxidase (CCO). This interaction enhances mitochondrial respiration and increases the production of adenosine triphosphate (ATP), which fuels cellular activities. In addition to ATP, photobiomodulation also modulates reactive oxygen species (ROS) and nitric oxide (NO), leading to anti-inflammatory, anti-apoptotic, and proliferative effects (Hamblin & Demidova, 2006).
While both RL and NIR activate CCO, the depth at which this activation occurs is different. Red light’s action is limited to epidermal and superficial dermal layers, whereas NIR reaches deeper into muscles, joints, and even bones, thus broadening its therapeutic potential (Chung et al., 2012).
3. Clinical Applications
Red light therapy is primarily used for dermatological and cosmetic purposes. Its applications include wound healing, treatment of acne, rosacea, psoriasis, and enhancement of collagen production. Studies have shown that red light significantly accelerates the healing of superficial wounds and reduces inflammation in skin conditions (Avci et al., 2013). A 2014 randomized controlled trial by Barolet and Boucher demonstrated improved wound closure and reduced erythema in patients treated with 630 nm red light.
In contrast, near-infrared light therapy is more effective for treating musculoskeletal conditions such as arthritis, muscle recovery, joint pain, and nerve injuries. Its deep penetration enables it to reach internal tissues and stimulate systemic effects. For example, a study by Leal Junior et al. (2009) showed that 810 nm and 904 nm NIR light significantly reduced inflammation and improved muscle performance in athletes.
4. Dosimetry and Treatment Parameters
The effectiveness of both RL and NIR therapy depends on parameters such as wavelength, power density, energy density, duration, and treatment frequency. However, due to differences in tissue penetration, the optimal parameters differ. Red light usually requires lower power densities and shorter exposure times due to its limited penetration. Near-infrared light typically necessitates higher power densities and longer durations to reach target tissues.
Photobiomodulation follows a biphasic dose response, meaning that both underdosing and overdosing can lead to suboptimal or even adverse effects. Therefore, precise calibration of treatment parameters based on the depth and type of tissue is essential for maximizing clinical outcomes (Huang et al., 2009).
5. Safety and Side Effects
Both red and near-infrared light therapies are considered safe when used appropriately. Common side effects are rare and typically mild, including temporary redness, tingling, or warmth at the treatment site. Importantly, neither red nor NIR light is ionizing, meaning it does not damage DNA or increase cancer risk. However, incorrect use (e.g., excessive exposure) can lead to thermal injury or phototoxicity, particularly with high-power devices (Anders et al., 2015).
6. Emerging Applications and Future Directions
Recent studies have explored the use of NIR light in neurodegenerative diseases such as Alzheimer's and Parkinson’s due to its ability to penetrate the skull and improve cerebral blood flow and mitochondrial function in neurons. A study by Salehpour et al. (2018) found cognitive improvements in dementia patients treated with transcranial NIR.
Red light, on the other hand, is gaining popularity in aesthetic medicine for promoting hair growth and reducing signs of aging. It has also been investigated for treating oral mucositis in cancer patients and reducing radiation-induced dermatitis.
Conclusion
In summary, both red and near-infrared light therapies are valuable tools in modern medicine and wellness, with distinct but complementary properties. Red light is most effective for surface-level applications such as skin repair and anti-aging treatments, while near-infrared light is suited for deeper therapeutic targets, including muscles, joints, and even brain tissues. Their shared mechanisms of action through mitochondrial modulation underscore their therapeutic versatility. As research progresses, we can expect more precise treatment protocols and broader adoption across clinical disciplines.
References
Hamblin, M.R. (2017). Mechanisms and applications of the anti-inflammatory effects of photobiomodulation. AIMS Biophysics, 4(3), 337–361.
Hamblin, M.R., & Demidova, T.N. (2006). Mechanisms of low level light therapy. Proc. SPIE 6140, Photonics in Dermatology and Plastic Surgery.
Chung, H., Dai, T., Sharma, S.K., Huang, Y.Y., Carroll, J.D., & Hamblin, M.R. (2012). The Nuts and Bolts of Low-level Laser (Light) Therapy. Annals of Biomedical Engineering, 40(2), 516–533.
Avci, P., Gupta, A., Sadasivam, M., Vecchio, D., Pam, Z., Pam, N., & Hamblin, M.R. (2013). Low-level laser (light) therapy (LLLT) in skin: stimulating, healing, restoring. Seminars in Cutaneous Medicine and Surgery, 32(1), 41–52.
Leal Junior, E.C.P., Lopes-Martins, R.A.B., Dalan, F., et al. (2009). Effect of 830 nm low-level laser therapy in exercise-induced skeletal muscle fatigue in humans. Photomedicine and Laser Surgery, 27(4), 571–576.
Huang, Y.Y., Chen, A.C.H., Carroll, J.D., & Hamblin, M.R. (2009). Biphasic dose response in low level light therapy. Dose-Response, 7(4), 358–383.
Anders, J.J., Lanzafame, R.J., & Arany, P.R. (2015). Low-level light/laser therapy versus photobiomodulation therapy: The semantics and science. Photomedicine and Laser Surgery, 33(4), 183–184.
Salehpour, F., Mahmoudi, J., Kamari, F., Sadigh-Eteghad, S., Rasta, S.H., & Hamblin, M.R. (2018). Brain Photobiomodulation Therapy: a Narrative Review. Molecular Neurobiology, 55(8), 6601–6636.
