The use of light in medicine dates back to ancient civilizations, when sunlight was employed to treat various ailments. Today, with advancements in technology, the medical community has harnessed specific wavelengths of light to develop targeted treatments for a wide range of conditions.
From ultraviolet (UV) to visible (VL) and infrared (IR) light, each wavelength interacts uniquely with human tissues, offering therapeutic benefits and presenting potential risks. Understanding these interactions is important for optimizing the use of light in medical applications while ensuring patient safety.
How Different Wavelengths Penetrate Skin and Body
Understanding how various wavelengths penetrate different layers of skin and tissue is key to maximizing therapeutic benefits while minimizing risks. Each wavelength interacts uniquely with human tissue, providing specific advantages and challenges in medical applications.
Ultraviolet (UV) Light
UV light, ranging from 100–400 nanometers (nm), is divided into three categories¹:
- UV-A (320–400 nm): Penetrates the dermis; used in phototherapy for conditions like psoriasis and vitiligo. Prolonged exposure can cause skin aging and increase cancer risk.
- UV-B (290–320 nm): Penetrates the epidermis; effective in treating skin conditions by slowing cell growth. Also administered in controlled doses to prevent sunburn and lower cancer risk.
- UV-C (100–290 nm): Primarily used for sterilization due to its germicidal properties. Science has shown 208-210 nm range has strong germicidal effects, able to inactivate bacteria and viruses on skin without harming human tissue.²
Visible Light (VL)
Visible light takes up the 400–700 nm spectrum and is perceived as different colors, each offering unique therapeutic benefits¹:
- Blue light (440–500 nm): Penetrates the upper dermis; effective for neonatal jaundice and acne. Antibacterial properties also help eliminate bacteria on the skin's surface.
- Green light (500–570 nm): Penetrates the upper dermis and is used to treat pigmentation issues by targeting melanocytes.
- Yellow light (570–590 nm): Penetrates the dermis and is known for its ability to stimulate collagen production, improve skin texture and also has a calming effect on the nervous system.
- Red light (620–750 nm): Penetrates the dermis and subcutaneous tissue, known for anti-inflammatory and wound-healing properties.
Infrared (IR) Light
Infrared light ranges from 700 nm to 1 mm and is categorized into three types¹:
- Near-Infrared (NIR) light (700–1.400 nm): Penetrates muscles, nerves, and bones, and can be effective for pain management and deep tissue repair.
- Mid-Infrared (MIR) light (1,400–3,000 nm): Provides thermal benefits; used in therapies requiring moderate heat.
- Far-Infrared (FIR) light (3,000 nm–1 mm): Penetrates surface layers of the skin, providing gentle heating beneficial for circulation and reducing stiffness.
Medical Applications of Different Wavelengths
Various wavelengths of light are harnessed in different medical applications that leverage their unique properties to treat numerous conditions.
Optical Biosensors
Optical biosensors are advanced analytical devices that use light to detect and analyze biological molecules and/or chemical substances. These sensors measure changes in light properties, such as absorbance, fluorescence, luminescence, or reflectance, caused by the interaction between a target analyte and a biorecognition element on the sensor surface.
Optical biosensors are highly valued in healthcare, environmental monitoring, and biotech for their high sensitivity, specificity, and real-time analysis capabilities. Factors such as color temperature, which affects fluorescence excitation and signal stability, can influence their performance, making them crucial tools for noninvasive, multifaceted, and continuous health monitoring⁴.
Photobiomodulation (PBM) for Wound Care
Light therapy is emerging as a promising technique for accelerating wound healing, particularly for severe and chronic wounds that are challenging to treat with conventional methods. Light therapy uses specific wavelengths of light to interact with tissues and cells, promoting natural healing processes by accelerating mitochondrial production of ATP and thereby reducing inflammation, minimizing scarring, and accelerating tissue repair.
Unlike traditional methods, light therapy is minimally invasive and often provides faster healing times. Wound care light therapy applications include treating burns, surgical wounds, and even non-healing wounds, making it a valuable tool in modern wound care.⁵
Photobiomodulation in Neurological Applications
PBM therapy is emerging as a catalytic, non-invasive treatment for various neurological disorders, including Alzheimer's, Parkinson's, and different traumatic brain injuries.
This innovative therapy involves the use of low-intensity red or near-infrared (NIR) light to stimulate neural activity and enhance brain function. By targeting cytochrome c oxidase in mitochondria, PBM therapy promotes cellular survival, reduces apoptosis, alleviates oxidative stress, and suppresses inflammation, potentially leading to significant improvements in cognitive and motor functions.
Clinical studies have shown PBM's potential to improve memory, attention, and mood in Alzheimer's patients, reduce motor impairment in Parkinson's patients, and enhance cognitive functions in TBI patients. As research progresses, PBM therapy may offer new hope for individuals suffering from debilitating neurological conditions.⁶
Bioluminescence in Medicine
Bioluminescence, the natural phenomenon by which living organisms emit light, has recently gained traction in medical research due to its potential in diagnostics, imaging, and therapeutic techniques.
Most types of bioluminescence involve a chemical reaction between luciferin, a light-emitting molecule, and luciferase, an enzyme, which produces light efficiently without significant heat generation.⁹
Observed by figures of antiquity like Aristotle and Pliny the Elder, bioluminescence has transitioned from a curiosity of the natural world to a tool with powerful potential in modern medicine. Bioluminescent markers enable researchers to visualize and track diseases by incorporating luciferase genes into cells, which emit light when a substrate like luciferin is present. This non-invasive imaging technique allows for real-time monitoring of disease progression and treatment efficacy in live animal models, providing critical insights into cancer growth, metastasis, and infectious disease dynamics.⁹
Additionally, bioluminescence facilitates drug discovery and development, enabling rapid and sensitive screening of potential therapeutic agents. As advancements continue, bioluminescence could potentially transform non-invasive diagnostics.
Potential Risks of Light Therapy
UV Radiation Risks
UV radiation can cause acute skin damage, manifesting as erythema similar to sunburn. Chronic exposure may lead to photo-aging and a higher risk of skin cancers like melanoma.
The eyes are particularly sensitive to UV radiation. Too much UV light could lead to conditions like photokeratitis and conjunctivitis, which can also contribute to cataract formation.⁷
Visible Light Risks
Blue light, though beneficial for specific medical treatments, can cause retinal damage with prolonged exposure, requiring regulated exposure to prevent eye strain and potential macular degeneration. Additonally, some people have a nausea reaction to blue light.⁷
Infrared Radiation Risks
The primary concern with infrared radiation is thermal damage, including skin burns and heat-induced rashes. Chronic exposure might lead to conditions like erythema ab igne (EAI), increasing the risk of skin cancer. However, these risks are generally associated with improper use or excessive exposure.⁷
The Transformative Potential of Light in Medicine
The powerful potential of light in medicine is to offer non-invasive diagnostics, real-time disease monitoring, and targeted treatments.
While understanding and mitigating associated risks is crucial for patient safety, the integration of light-based technologies promises improved patient outcomes, reduced treatment times, and lower healthcare costs, promising a brighter future for medical advancements.
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Resources:
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- Bernerd, F., Passeron, T., Castiel, I., & Marionnet, C. (2022). The Damaging Effects of Long UVA (UVA1) Rays: A Major Challenge to Preserve Skin Health and Integrity. International Journal of Molecular Sciences, 23(15), 8688. https://doi.org/10.3390/ijms23158688
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- Hamblin, M. R., & Huang, Y. Y. (2024). Phototherapy for age-related brain diseases: Challenges, successes and future. Ageing Research Reviews, 86, 101945.
- Lawrence Berkeley National Laboratory. (n.d.). Ultraviolet radiation. https://ehs.lbl.gov/resource/documents/radiation-protection/non-ionizing-radiation/ultraviolet-radiation/
- Barolet, D., Christiaens, F., & Hamblin, M. R. (2016). Infrared and skin: Friend or foe. Journal of Photochemistry and Photobiology B: Biology, 155, 78-85.
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