Frequently Asked Questions

Q: What conditions can be treated with LLLT?

A: LLLT can have a positive effect on several pathological conditions due to its anti-inflammatory effects and stimulating effects on many cell types. The amount of scientific evidence for LLLT varies, but it is currently strongest in musculoskeletal disorders like muscle pain, arthritis, tendinitis, carpal tunnell syndrome and neck & back pain. There are currently published more than 60 controlled trials with these musculoskeletal disorders in scientific journals. LLLT works well when applied according to WALT guidelines and together with other commonly used treatments (except steroids) for these conditions. In sports medicine, LLLT can be used for acute soft tissue injuries and muscle recovery after training and competition. Skin conditions and wound-healing is another area where LLLT is widely used. Your laser therapist may have positive individual experience in other specific areas for LLLT, although solid scientific evidence may still be lacking.

Q: What is Low Level Laser Therapy?

A: The definition by The National Library of Medicine - Medical Subject Headings is: Treatment using irradiation with light at low power intensities and with wavelengths in the range 540 nm-830 nm. The effects are thought to be mediated by a photochemical reaction that alters CELL MEMBRANE PERMEABILITY, leading to increased mRNA synthesis and CELL PROLIFERATION. The effects are not due to heat, as in LASER SURGERY. Low-level laser therapy has been used in general medicine, veterinary medicine, and dentistry for a wide variety of conditions, but most frequently for wound healing and pain control.

The definition is correct but the effects do not end at 830 nm; most wavelengths tested have shown a biostimulative effect.

Q: Which is the correct term for this kind of therapy?

A: LLLT (Low Level Laser Therapy) is the dominant term in use today, but there is still a lack of consensus. The term "soft laser" was originally used to differentiate therapeutic lasers from "hard lasers", i.e. surgical lasers. Several different designations then emerged, such as "MID laser" and "medical laser". "Biostimulating laser" is another term, with the disadvantage that one can also give inhibiting doses. The term "bioregulating laser" has thus been proposed. Other suggested names are "low-reactive-level laser", "low-intensity-level laser", "photobiostimulation laser" and "photobiomodulation laser". "LPT - Laser Photo Therapy" is a recently suggested term, and winning acceptance. The question of nomenclature is far from solved.

Q: Is laser therapy scientifically well documented?

A: Basically yes. There are more than 130 double-blind positive studies confirming the clinical effect of LLLT. More than 3000 research reports are published. In recent years some 250 papers have annually been published in peer reviewed scientific journals. Since LLLT has a general effect, a wide range of treatments have been suggested, some well documented, some less documented and others anecdotal.

Q: Where do I find such documentation?

A: Abstracts from scientific papers can be found on PubMed.

Q: But I have heard that there are dozens of studies failing to find any effect of LLLT?

A: That is true. But you cannot just take a any laser and irradiate for any length of time and using any technique. A closer look at the majority of the negative studies will reveal serious flaw. But LLLT will naturally not work on everything. Competent research certainly has failed to demonstrate effect for several indications. However, as with any treatment, it is a matter of dosage, diagnosis, treatment technique and individual reaction.

Q: Can lasers replace acupuncture needles?

A: Recent research suggests that this is actually the case. The effects are not identical but similar.

Q: Which parameters are important in LLLT?

A: The most important factor is the dose (also called fluence or energy density). It is expressed in joules per cm2. The number of joules (J) is calculated as follows: number of milliWatt x seconds of application; e.g. 100 mW x 10 seconds = 1000 millijoules = 1 joule (J). The dose is the number of joules divided by the size of the irradiated area, expressed in cm2. Thus 1 J over an area of 0.25 cm2 = 1/0.25 = 4 J/cm2. The dose must be related to the depth of the actual location of the target.

Q: Which lasers can be used for LLLT?

A: A wide range of wavelengths can be used, but the most common types are:

  • GaAs 904 nanometres (pulsed infrared)
  • GaAlAs 780-820-870 nm (continuous infrared)
  • InGaAlP 630-685 nm (red)
  • HeNe 623.8 nm (red)

Q: Can therapeutic lasers damage the eye?

A: Yes and no! The following factors are of importance regarding the eye risk of different lasers:

  • The divergence of the light beam. A parallel light beam with a small diameter is by far the most dangerous type of beam. It can enter the pupil, in its entirety, and be focused by the eye's lens to a spot with a diameter of hundredths of a millimetre. The entire light output is concentrated on this small area. With a 10 mW beam, the power density can be up to 12,000 W/cm2
  • The output power (strength) of the laser. It is fairly obvious that a powerful laser (many watts) is more hazardous to stare into than a weak laser.
  • The wavelength of the light. Within the visible wavelength range, we respond to strong light with a quick blinking reflex. This reduces the exposure time and thereby the light energy which enters the eye. Light sources which emit invisible radiation, whether an infra-red laser or an infra-red diode, always entail a higher risk than the equivalent source of visible light. Radiation at wavelengths over 1400 nm is absorbed by the eye's lens and is thus rendered safe, provided the power of the beam is not too high. Radiation at wavelengths over 3,000 nm is absorbed by the cornea and is less dangerous.
  • The distribution of the light source. If the light source is concentrated, which is often the case in the context of lasers, an image of the source is projected on the retina as a point, provided it lies within our accommodation range, i.e. the area in which we can see clearly. A widely spread light source is projected onto the retina in a correspondingly wide image, in which the light is spread over a larger area, i.e. with a lower power density as a consequence. For example: a clear light bulb (which is apprehended as a more concentrated light source) penetrates the eye more than a so-called "pearl" light bulb. A laser system with several light sources placed separately, such as a multiprobe (the probe is the part of the laser you hold and apply to the area to be treated: a single probe means there is only one laser diode in the probe, as opposed to a multiprobe, which has several laser diodes) with several laser diodes, can, seen as a whole, be very powerful but at the same time constitute a smaller hazard to the eye than if the entire power output was from one laser diode, because the diodes' separate placement means that they are reproduced in different places on the retina.

Q: I have heard that if it's a class 3B laser then it's fine, otherwise it has no effect.

A: This is incorrect and has lead to a situation where manufacturers have produced lasers only to meet the 3B classification. Let us look at a couple of examples:

  • A GaAlAs laser with a wavelength of 830 nm, an output of 1 mW and a well collimated beam (1 mrad divergence) is classified as laser class 3B as it is judged to be hazardous to the eye. The reason for this is partly the collimated beam, and partly the wavelength, which is just outside the visible range and hence provokes no blink reflex in strong light.
  • A HeNe laser with a wavelength of 633 nm, an output of 10 mW and divergent beams (1 rad divergence, which corresponds to a cone of light with a top angle of about 57°) is classified as laser class 3A because, owing to its divergence, it cannot damage the eye.

With the recent advent of "high power low power lasers", i.e. GaAlAs lasers in the range 500-5000 mW there is another story. These lasers are indeed dangerous for the eye and should only be used by qualified persons and with proper protective measures taken.

In conclusion, most of these lasers are not harmful but WALT recommends all therapists to let patients use protective goggles to avoid any risk of eye injuries.

Q: How deep into the tissue can a laser penetrate?

A: The depth of penetration of laser light depends on the light's wavelength, on whether the laser is super-pulsed, and on the power output, but also on the technical design of the apparatus and the treatment technique used. A laser designed for the treatment of humans is rarely suitable for treating animals with fur. There are, in fact, lasers specially made for this purpose. The special design feature here is that the laser diode(s) obtrude from the treatment probe rather like the teeth on a comb. By delving between the animal's hair, the laser diode's glass surface comes in contact with the skin and all the light from the laser is "forced" into the tissue.

A factor of importance here is the compressive removal of blood in the target tissue. When you press lightly with a laser probe against skin, the blood flows to the sides, so that the tissue right in front of the probe (and some distance into the tissue) is fairly empty of blood. As the haemoglobin in the blood is responsible for most of the absorption, this mechanical removal of blood greatly increases the depth of penetration of the laser light.

It is of no importance whether the light from a laser probe, held in contact with skin is a parallel beam or not.

There is no exact limit with respect to the penetration of the light. The light gets weaker and weaker the further from the surface it penetrates. There is, however, a limit at which the light intensity is so low that no biological effect of the light can be registered. This limit, where the effect ceases, is called the greatest active depth. In addition to the factors mentioned above, this depth is also contingent on tissue type, pigmentation, and dirt on the skin. It is worth noting that laser light can even penetrate bone (as well as it can penetrate muscle tissue). Fat tissue is more transparent than muscle tissue.

For example: a HeNe laser with a power output of 3.5 mW has a greatest active depth of 6-8 mm depending on the type of tissue involved. A HeNe laser with an output of 7 mW has a greatest active depth of 8-10 mm. A GaAlAs probe of some strength has a penetration of 35 mm with a 55 mm lateral spread. A GaAs laser has a greatest active depth of between 20 and 30 mm (sometimes down to 40-50 mm), depending on its peak pulse output (around a thousand times greater than its average power output). If you are working in direct contact with the skin, and press the probe against the skin, then the greatest active depth will be achieved. Clothes will reduce penetration between 80 and 100% depending on thickness and colour.

Q: Can LLLT cause cancer?

A: The answer is no. No mutational effects can result from light with wavelengths in the red or infra-red range and of doses used within LLLT. But what happens if an undiagnosed area of cancer is irradiated by LLLT? Can the cancer's growth be stimulated? The effects of LLLT on cancer cells in vitro have been studied, and it was observed that they can be stimulated by laser light. However, with respect to a cancer in vivo, the situation is rather different. Experiments on rats have shown that small tumours treated with LLLT can recede and completely disappear, although laser treatment had no effect on tumours over a certain size. It is probably the local immune system which is stimulated more than the tumour. The situation is the same for bacteria and virus in culture. These are stimulated by laser light in certain doses, while a bacterial or viral infection is cured much quicker after the treatment with LLLT. So in conclusion, LLLT does not cause cancer but irradiation over known or suspected areas of malignancies should be avoided.

Q: What happens if too high doses are applied?

A: There will be a biosuppressive effect. That means that, for instance, the healing of a wound will take longer time than normally. Very high doses on healthy tissues will not damage them.

Q: How often should LLLT be applied?

A: For acute conditions treatment can be applied often, daily or every other day until the problem is resolved. For chronic conditions initial treatment is recommended no more than 2-3 sessions per week and with longer intervals as the situation is improving.

Q: Are there any contra indications?

A: Cancer should not be treated by anyone but the specialist, for legal reasons. Pregnant women is not a contra indication, if used with common sense. Pacemakers are electronic, do not respond to light. Epilepsy may be a contra indication but not documented as such. Diabetes is sometimes found as a contraindication in old literature. However, the side effects of diabetes such as impaired wound healing and micro-circulation are excellent indications for LLLT. The most valid contra indication is lack of medical training

Q: Does LLLT cause a heating of the tissue?

A: Due to increased circulation there is usually an increase of 0.5-1 centigrades locally. The biological effects have nothing to do with heat. GaAlAs lasers in the 300-500 mW range will cause a noticeable heat sensation, particularly in hairy areas, dark tattoo and on sensitive tissues such as lips. The amount of melanin in the skin is an important factor; dark skin will be more easily "heated" than light skin.