Red light therapy (RLT), also known as photobiomodulation (PBM), is a non-invasive treatment that accelerates the body’s natural healing processes. Bruises, common consequences of minor trauma, result from a disruption beneath the skin’s surface that the body must resolve. RLT uses specific light wavelengths to influence cellular activity, potentially speeding up the clearance of discoloration and associated swelling.
The Biological Process of Bruise Formation
A bruise, medically termed a contusion or hematoma, begins with trauma that ruptures small blood vessels, called capillaries, beneath the skin. This damage allows blood to leak into the surrounding tissues, which is what causes the initial visible discoloration. The initial appearance is often red or purple because the hemoglobin in the leaked red blood cells is still rich in oxygen.
Within a day or two, the oxygen is depleted, and the hemoglobin changes color, resulting in the characteristic blue, black, or dark purple hue of a fresh bruise. The body’s immune system then initiates the cleanup process by sending specialized cells to break down the trapped blood. These cells metabolize the hemoglobin into a sequence of pigment byproducts.
The first major breakdown product is biliverdin, which gives the bruise a greenish tint, typically appearing after five to ten days. Biliverdin is further processed into bilirubin, which is yellow, before the bruise eventually fades to a brownish color from the iron-containing hemosiderin. The duration of the entire color-change sequence depends on the bruise’s size and location, but the body must efficiently clear these pigments and cellular debris for the bruise to fully disappear.
Cellular Mechanisms of Red Light Therapy
RLT works by delivering specific wavelengths of light energy, typically in the red (630–670 nanometers) and near-infrared (800–850 nanometers) spectrums, to stimulate cellular recovery. These wavelengths penetrate the skin and are absorbed by internal cellular components. This stimulation is known as photobiomodulation (PBM).
The primary cellular target is the enzyme cytochrome c oxidase, which is a component of the electron transport chain located within the mitochondria. When light energy is absorbed by this enzyme, it enhances mitochondrial oxidative metabolism, which is the process that generates cellular energy. This photochemical interaction increases the cell’s capacity to produce adenosine triphosphate (ATP), the main energy currency of the cell.
In the context of a bruise, this increase in cellular energy is theorized to accelerate the clearance of cellular debris and the breakdown pigments like biliverdin and bilirubin. The enhanced energy also supports the functions of immune cells responsible for removing the extravasated blood and damaged tissue. Furthermore, PBM is recognized for its ability to modulate localized inflammation and swelling, which often accompany a fresh bruise.
This anti-inflammatory effect is achieved by influencing signaling molecules and reducing oxidative stress within the damaged tissue. Improved cellular function, combined with increased local blood flow, helps transport nutrients to the injured area and remove waste products more efficiently. The overall result of this mitochondrial stimulation is a faster transition through the bruise’s color-change stages, leading to quicker resolution.
Clinical Evidence and Safe Application Methods
The efficacy of RLT for soft tissue trauma, including bruising, is supported by clinical observations showing that it speeds up the resolution of swelling and hematoma formation. Studies indicate that applying PBM soon after an injury can accelerate the fading of bruise discoloration compared to untreated areas. This makes RLT a valuable tool for managing post-injury recovery.
For home use, RLT devices utilize wavelengths between 630 nm and 850 nm, with near-infrared light offering deeper tissue penetration. A common therapeutic dosage range for surface-level healing is between 4 and 20 Joules per square centimeter, though this varies based on the device’s power output. Treatment sessions often last between 5 and 20 minutes for the affected area.
It is suggested to start treatment with one or two sessions daily in the first few days following the injury, then reducing the frequency as the bruise begins to fade. The light source should be held at the distance recommended by the manufacturer to ensure the light energy is delivered efficiently to the skin. It is important to treat the entire bruised area, including a small margin of surrounding healthy tissue.
Safety is paramount, and RLT devices use low-level, non-thermal light, meaning they do not generate heat that could cause burns. Users should wear protective eyewear to shield the eyes from the bright light, particularly when using near-infrared wavelengths which are invisible. If a bruise is accompanied by severe pain, increasing size, or does not begin to fade after two weeks, a medical professional should be consulted.