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The Difference Between Class III & Class IV Laser Therapy Systems

There are a lot of different laser therapy systems on the market today, each with varying specifications on their power and settings like continuous wave, pulsed, and super pulsed. With all these options and opposing claims, it’s hard to know what will work best for your clinic.

One of the significant differences between laser therapy systems is whether they are class III (3) or class IV (4) laser devices. Knowing the difference and how each will affect the type of treatment you can provide is essential when deciding on a laser therapy system.

Basics of Laser Classification

The FDA classifies lasers based on their potential to cause harm if misused, particularly to the skin and eyes. Class IIIb and class IV laser devices have the highest potential for injury if misused. Still, even lower classes, such as a class IIIa laser pointer or class II barcode scanner, can cause harm if viewed directly with magnifying optical aids or if the naked eye is exposed for a longer period.

By FDA regulations, any laser device class II or above must be labeled with a warning that includes the device’s class and power output. A laser pointer toy for cats and a surgical laser for skin ablation have the same labeling policies.

Specifically for classes IIIb and IV, laser devices pose a risk of injury if directly viewed for any period of time and are a skin hazard. In addition, class IV lasers can also cause damage if viewed indirectly.

As a healthcare provider, you don’t want to be hurting your patients, so the idea that a device can hurt them might be off-putting. But as with other powerful medical devices like X-rays, CT scans, and MRIs, the benefits greatly outweigh the risks with the proper precautions and training. Any laser therapy device you add to your practice should have comprehensive safety protocols and protective eyewear for both laser technicians and patients.

Differences Between Class III & Class IV Lasers

So what’s the difference between class III and class IV lasers? The most significant difference is their maximum power output. The FDA defines a class IIIb laser as a device with a power output between 5-500mW (0.005-0.5W) and a class IV laser as a device with a power output above 500mW (0.5W).

Maximum power output is separate from wavelength, so you might find class IIIb and class IV lasers with the same wavelength. Wavelength and power are both critical, but higher powers have a greater penetration depth when it comes to power. A higher power laser can effectively and safely reach further into the body, allowing a photochemical effect on muscle, bone, and even the brain. Higher powers also reduce the need to press the laser therapy wand into the skin, reducing the risk of bruising.

A less powerful laser can still benefit areas directly beneath the skin and less dense body regions, like the hands and wrists. But high power is necessary to get to and through thicker muscle and bone.

The Complexity of Laser Therapy Dosage

Since laser therapy is used to treat a wide variety of concerns all over the body, the dosage is more complex. As we’ve already discussed, power has a significant influence on the depth of penetration of the laser. Another aspect of laser dosage is wavelength. Some standard wavelengths in laser therapy are 635nm, 810nm, and 980nm.

What do the different wavelengths do? The wavelength determines the type of tissue that will respond and produce the photochemical healing effect. For example, light around 635nm is the preferred wavelength for treating skin conditions. Clinical studies will often vary the wavelength, power level, or both when the study aims to find the optimal dosage for a particular part of the body or a specific concern. One typical result from clinical studies on dosage is that the less optimal wavelength won’t produce any results, or it will produce minimal or placebo results.

Another aspect that makes laser therapy dosage tricky is how each person is unique. Skin tone, body type, and even hair color and type can play a role in determining the effective dosage for laser therapy. How a patient responds to treatment can call for adjustments as well.

Additionally, condition-specific aspects can affect the dosage. The size of an injury, progression of chronic disease, or whether the condition is acute or chronic plays a role in how laser therapy should be used to treat it.

What Laser Therapy System Does My Practice Need?

Unless you only treat a limited number of conditions with laser therapy, a system that allows you to adjust the power output and switch between wavelengths is ideal for treating the widest variety of conditions and people.

If you’re highly specialized, such as a hand surgeon, you might not need a particularly versatile device as most of your patients will have similar concerns. But for a more generalized practitioner, like a chiropractor, veterinarian, or sports medicine specialist, who sees and treats various people (or animals) and conditions, the more customizable your treatment protocols will allow you to help more patients.

When purchasing a laser therapy device, the most important thing is to ensure the device is registered with the FDA. Devices that are not registered do not have protections in place if the machine were to malfunction or the device is improperly labeled, causing harm or failure to produce results. Always make medical device purchases from reputable companies for your safety and your patients’ safety.

Looking to add laser therapy to your practice? Check out our class IV laser therapy systems in the link below.


This blog was originally published on December 2, 2019, and was last updated on June 2, 2022.

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