Red Light Therapy (RLT), also known as photobiomodulation, is a non-invasive treatment that uses specific wavelengths of low-level red and near-infrared light to stimulate cellular processes. Cortisol is widely recognized as the body’s primary glucocorticoid hormone, released in response to physical or psychological stressors to manage the “fight or flight” response. This article explores the current scientific understanding of the relationship between RLT and this stress hormone.
Understanding Cortisol’s Physiological Role
Cortisol is a steroid hormone produced and released by the adrenal glands, which sit atop the kidneys. Its function is far-reaching, regulating metabolism, blood pressure, and inflammatory responses. The hormone is especially important in the body’s acute reaction to stress, mobilizing energy reserves quickly to prepare the body for immediate action.
The release of cortisol is tightly controlled by a complex communication system known as the Hypothalamic-Pituitary-Adrenal (HPA) axis. When stress is perceived, the hypothalamus signals the pituitary gland, which then signals the adrenal glands to secrete cortisol. This feedback loop is designed to shut off the stress response once the threat has passed and the body has returned to balance.
The problem arises when chronic, prolonged stress prevents the HPA axis from turning off the response. Persistent elevation of cortisol can lead to negative health outcomes, including dysregulation of the immune system, poor sleep quality, and changes in mood. Therefore, therapies that can help normalize or regulate an overactive stress response are being explored to support overall wellness.
How Red Light Therapy Modulates the Stress Response
The theoretical mechanism for RLT’s influence on the stress response is rooted in its interaction with the cell’s energy centers, the mitochondria. Red and near-infrared light (typically 630 nm to 850 nm) penetrates the skin and is absorbed by a specific enzyme within the mitochondria called cytochrome c oxidase. This absorption is the foundation of photobiomodulation, stimulating the enzyme and enhancing the efficiency of the cellular respiration process.
This action leads to an increase in the production of Adenosine Triphosphate (ATP), the cell’s primary energy currency. By boosting cellular energy production, RLT supports cells in performing their functions more effectively, including those involved in managing stress and inflammation.
A secondary effect is the reduction of oxidative stress within the cells. Chronic stress is linked to increased cellular damage, which can lead to inflammation. By improving mitochondrial function, RLT helps to mitigate this cellular strain, which in turn can calm the body’s overall stress burden. This anti-inflammatory and energy-boosting effect is thought to indirectly stabilize the HPA axis, allowing for a more balanced hormonal output.
The calming effect of RLT is also hypothesized to influence the autonomic nervous system by promoting parasympathetic activity, the “rest-and-digest” state. By shifting the nervous system away from the sympathetic “fight-or-flight” dominance, RLT helps create a physiological state that is less conducive to high cortisol production.
Research Findings and Treatment Protocols
Current research suggests that red light therapy can play a role in regulating the body’s stress response, including the potential to lower elevated cortisol levels. Preliminary studies indicate that RLT treatment can lead to a reduction in certain stress markers and a more balanced endocrine profile. For example, some human studies have demonstrated that participants exposed to red light exhibited significantly lower cortisol production compared to control groups. However, the body of high-quality, long-term clinical trials specifically measuring RLT’s effect on cortisol is still developing.
Much of the evidence comes from studies focused on related outcomes, such as improved sleep quality, reduced inflammation, and better mood, all closely linked to cortisol regulation. The evidence points toward a modulatory effect, helping to normalize levels that are chronically high rather than suppressing them entirely.
For individuals considering using RLT to address stress, specific protocols derived from research can guide application. The most commonly studied therapeutic wavelengths are red light (630–660 nm) and near-infrared light (810–850 nm). Near-infrared light penetrates deeper into tissue, making it suitable for targeting underlying structures like the brain and HPA axis components. A typical treatment duration is 10 to 20 minutes per session. Consistent use, often three to five times per week, is advised to see potential benefits related to stress and hormonal balance.
When targeting the stress response, the light may be applied directly to the head, forehead, or the back of the neck to affect brain function and the underlying HPA axis. Using RLT earlier in the day (7 AM and 3 PM) is suggested to align with the body’s natural circadian rhythm for cortisol output. Red light therapy is generally considered safe and non-invasive, with no major side effects reported when used according to device guidelines.