Red Light Therapy (RLT), also known as Low-Level Laser Therapy (LLLT) or Photobiomodulation (PBM), uses specific wavelengths of light to interact with biological tissue. This therapy utilizes light in the red and near-infrared (NIR) spectrum (typically 600 to 1000 nanometers) to elicit a photochemical response. Given RLT’s fundamental mechanism of stimulating cellular activity, there is concern that it could potentially accelerate or worsen malignant conditions. This article examines the scientific evidence and the current consensus regarding the use of RLT in the context of cancer.
How Red Light Therapy Affects Cellular Metabolism
The mechanism of RLT begins at the cellular level, specifically within the mitochondria. Red and near-infrared light wavelengths penetrate the skin and underlying tissues, reaching the mitochondria inside various cell types. The primary target for this light energy is cytochrome c oxidase (CCO), a respiratory enzyme and a key component in the mitochondrial electron transport chain.
CCO acts as the main chromophore for RLT wavelengths. When CCO absorbs photons, it displaces nitric oxide (NO), which normally binds to CCO and inhibits its function. Once NO is displaced, the electron transport chain accelerates, rapidly increasing the production of adenosine triphosphate (ATP).
This boost in ATP provides energy for cellular functions, including repair and growth. The photonic energy also causes a temporary modulation of reactive oxygen species (ROS). This transient, low-level increase in ROS can activate signaling pathways that promote cellular resilience and tissue healing. This fundamental process of increasing cellular energy and promoting cell proliferation raises the concern regarding RLT’s use near malignant lesions.
Current Evidence on Tumor Acceleration
The scientific debate regarding RLT and cancer stems from the therapy’s core function: the stimulation of cell proliferation and metabolism. Because cancer is characterized by rapid, uncontrolled cell growth, the theoretical risk is that the energy boost from RLT could potentially support and accelerate the division of malignant cells. Consequently, the general professional consensus advises avoiding RLT use directly over any known or suspected malignant lesion.
Preclinical studies investigating this risk have shown mixed results, often dependent on the specific light dose and cancer model used. Some older animal studies suggested that RLT could accelerate tumor growth under certain conditions, reinforcing the initial caution. However, other studies using different parameters, such as a mouse model of nonmelanoma skin cancer, found no measurable effect on tumor growth when RLT was applied.
More recent laboratory and animal research has further complicated the picture, suggesting that RLT may even possess anti-cancer properties in specific contexts. For example, some studies on melanoma cell lines have demonstrated that applying RLT at particular high fluences can inhibit cell proliferation and induce programmed cell death. The current clinical evidence is strongest in supportive care, where RLT is safely and effectively used to manage cancer treatment side effects like oral mucositis, with no evidence suggesting it worsens the underlying cancer. Ultimately, the theoretical risk of promoting an existing tumor, particularly at sub-optimal or stimulatory doses, remains the reason for the prevailing caution in the absence of large-scale human clinical trials.
Practical Safety Measures and Contraindications
A cautious approach is recommended when considering RLT, especially for individuals with a history of cancer. The most important safety measure is to never apply red light therapy directly over an area with a known or suspected malignant lesion. This contraindication extends to any area where cancer has recently been treated or surgically removed, due to the possibility of residual malignant cells.
Patients actively undergoing conventional cancer treatments, such as chemotherapy or radiation, must consult their oncology team before beginning RLT. Although RLT is used in supportive care, applying it to tissues weakened by aggressive therapies could be detrimental or interfere with the intended treatment effect. RLT should never be used as a substitute for conventional cancer treatment.
Photosensitizing Medications
Other contraindications involve medications that increase the skin’s sensitivity to light, known as photosensitizing drugs. Certain antibiotics, antifungals, or chemotherapy agents can make the skin highly reactive to RLT, potentially leading to localized damage or burns. Consulting with a healthcare provider or oncologist is necessary to ensure RLT is appropriate, especially for those taking prescription medications.