Back to Basics: Understanding the Mechanisms of Laser Therapy

The power of light may be the missing piece to managing pain at your practice.

Laser therapy is a proven approach that uses light energy to stimulate biological processes at the cellular level to relieve pain, reduce inflammation, and accelerate healing.

However, not all therapy lasers offer the same therapeutic capabilities. Different specifications, such as wavelength, power, and output mode, can affect the treatment duration and number of sessions needed to achieve desired results. These can also determine the indications that the laser is suitable to address.

With a wide variety of light-based therapies to consider, it can be difficult to identify which is best for your patients and your practice. A solid understanding of the basic mechanisms of laser therapy is vital for practitioners considering this modality for their practice.

Laser Therapy 101

Laser therapy uses an induced emission of electromagnetic radiation to transfer energy to biological cells to stimulate photobiomodulation.

Photons are absorbed by the mitochondria and activate enzymes to increase ATP production. This starts a cascade of molecular reactions that improve cell function and enhance the body’s healing processes. Some of these effects can include:

  • Increased tissue regeneration and wound healing by stimulating fibroblast development.
  • Reduced inflammation and edema by stimulating blood flow and lymphatic drainage.
  • Induced analgesia by stimulating the release of endorphins and enkephalins to block the transmission of pain sensations to the brain.

Laser Classifications

The FDA recognizes four major classes of lasers (Classes I through IV) with three subclasses (Classes IIA, IIIA, and IIIB). Most therapy lasers fit within either Class IIIB or Class IV.

The higher the laser class, the higher the average power output. Class IIIB lasers offer a power output between 5 mW and 500 mW. Class IV includes all lasers that exceed 500 mW.


Wavelength plays a fundamental role in determining whether the emission can successfully transfer energy to the tissue. Additionally, it is the most important criteria for determining the depth of penetration.

Some wavelength frequencies are more susceptible to absorption by chromophores than others. For example, the absorption spectrum of oxygenated hemoglobin peaks between 400 nm and 600 nm. On the other hand, water molecules strongly absorb wavelengths above 1100 nm. 

Other chromophores, such as melanin, can also impact absorption but to a much smaller degree. Energy that is absorbed by these chromophores is energy that is unable to reach the target tissue.

Light scattering and absorption occurs in all tissues. Precisely choosing a wavelength based on absorption characteristics can minimize scatter and absorption allowing energy to penetrate to deeper tissue.

Most therapy lasers leverage wavelengths within the approximate range of 600 nm to 1200 nm. This has been deemed the “therapeutic window” because these frequencies have maximal ability to penetrate tissue and trigger biological effects.

Power and Fluence

Power (measured in watts) refers to the rate at which energy (measured in Joules) is delivered.

Fluence refers to energy density and is measured by Joules per centimeter squared. To obtain sufficient therapeutic results, sufficient light energy must be delivered to the target tissue. This is sometimes referred to as the “therapeutic threshold” or “therapeutic dose window.”

Energy density is affected by treatment time. For example, with the right parameters Class IIIB lasers have the potential to deliver the same J/cm2 as a Class IV laser. However, it will take significantly more time because it will be operating at a lower power (i.e. Joules of energy per second.)

Selecting fluence is vital to the efficacy of the treatment as well as the safety of the patient. A number of factors must be taken into consideration, including tissue type, pigmentation, spot size, output mode, and the characteristics of the condition being addressed.

Output Mode

Continuous modes deliver a constant beam of laser energy at a fixed level of power, while pulsed diodes emit a series of high-intensity pulses. Both modes have therapeutic benefits, but the high peak power of pulsed emissions allow for more effective penetration of laser energy while the average output is comparatively low.

Pulsed lasers allow more energy to penetrate deeper than continuous emissions of the same wavelength and same average power. With a percentage of the energy being absorbed by superficial tissues, the high peak power allows for more energy to reach the target tissue while pulsing minimizes risk of thermal damage. 

Some studies also suggest that cells may become less responsive to the steady stimuli of a continuous beam. For these reasons, pulsed diodes are growing in popularity.

Laser at the Private Practice

As technologies evolve, therapy lasers are becoming more efficient in their therapeutic capabilities while remaining safe for the patient and intuitive to the operator. With more opportunities to customize treatment parameters, practitioners can offer personalized protocols that address patients’ unique symptomology.

A thorough understanding of the mechanisms of laser therapy will empower practitioners to analyze and identify what is needed to deliver the best possible outcomes for each patient.

Subscribe for Updates

Related Posts

MLS Wound Progress

Tom, a Bracco Italiano with a Trauma Wound to the Left Knee

Tom suffered an injury during a hunt, probably due to hitting a stone or a branch. Tom underwent surgery, but because of the extent and the position of the wound, and because of the owners’ lack of attention during the post-op phase, the wound reopened. Read how MLS Laser Therapy helped reheal his post-op wound

Read More »